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Williams, Kevin John. "Biological and genetic studies of wheat resistance to Heterodera avenae." Title page, summary and contents only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phw7238.pdf.
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Marino, Dante. "Screening of Germplasm Accessions from the Brassica Species for Resistance against PG3 and PG4 Isolates of Blackleg." Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29053.
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Blackleg is a disease of canola and rapeseed cultivars that is caused by the fungus Leptosphaeria maculans (Desm.) Ces. & de Not., and it is by far the most destructive pathogen of canola in North America. In recent years, blackleg strains belonging to pathogenicity groups (PG) 3 and 4 have been discovered in North Dakota. Recent outbreaks of the disease have added a sense of urgency to characterize the risk these new strains represent for the canola industry and to identify sources of resistance against them. Thus, the objectives of this study were to screen germplasm collections of Brassica rapa, B. napus. and B. juncea for their reaction to PG3 and PG4 and to evaluate the reaction of a sample of currently used canola commercial cultivars grown in North Dakota to PG3 and PG4 as means to estimate the risk these new strains represent. All canola germplasm and commercial cultivars were evaluated in replicated trials in greenhouse conditions using cotyledon bioassays. In 2009 and 2010, the effect of these strains, using five inoculation sequences, on the reaction of canola seedlings was also evaluated. Field trials were not conducted because of the limited geographical distribution of the new strains. No adequate sources of resistance were identified among the 277 B. rapa and 130 B. napus accessions evaluated; however, 22 of the 406 accessions of Brassicajuncea evaluated were considered to have moderate levels of resistance. B. juncea seedlings that survived these inoculations were self-pollinated and their progeny (F1) were also screened. As before, surviving seedlings were self-pollinated. These F2 seeds are the elite materials that could be used in future breeding programs. The complementary study evaluating the role of sequence inoculations in reaction of canola seedlings to blackleg indicated that an increased susceptibility to PG3 occurred when seedlings were first inoculated with PG4; however, reaction to PG4 was not enhanced by a prior inoculation with PG3. All 75 commercial cultivars evaluated were susceptible to PG3 and PG4, indicating that the risk these new strains represent to the canola industry of the region is serious. Further, when a subsample of 16 cultivars were challenged with PG2, they were either resistant or moderately resistant, suggesting the ratings the industry are using relate to reaction of those cultivars to PG2 but not to the new strains; thus, growers should use caution when using these ratings while deciding on which cultivars to plant.North Dakota State University. Department of Plant Pathology
USDA North Central Canola Research Program
Northern Canola Growers Association
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Galagedara, Nelomie Nayanathara. "Identification of Quantitative Trait Loci for Resistance to Tan Spot in Durum Wheat." Thesis, North Dakota State University, 2018. https://hdl.handle.net/10365/28765.
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Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is a major foliar disease on wheat. The pathosystem involves three pairs of necrotrophic effector (NE) and host sensitivity (S) gene interactions, namely Ptr ToxA-Tsn1, Ptr ToxB-Tsc2 and Ptr ToxC-Tsc1. Additionally, genetic factors conferring race-nonspecific resistance have been identified. The objectives of this study were to map tan spot resistance QTL and investigate the role of NE-S interactions in disease in durum using association and bi-parental mapping. Evaluation of a worldwide collection of durum accessions allowed identifying highly resistant nineteen lines to multiple Ptr races. Association mapping revealed genomic regions on chromosomes 1A, 2B and 3B significantly associated with resistance to tan spot, which likely correspond to Tsc1, Tsc2 and racenonspecific resistance. Using a bi-parental population derived from Ben and PI 41025, we found that ToxA-Tsn1 interaction plays no significant role in disease, instead a major race-nonspecific QTL on chromosome 5A was identified.
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Van, Eeden C. (Christiaan). "The construction of gene silencing transformation vectors for the introduction of multiple-virus resistance in grapevines." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/53764.
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Thesis (MSc)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: Viruses are some of the most important pathogens of grapevines. There are no effective chemical treatments, and no grapevine- or other natural resistance genes have been discovered against grapevine infecting viruses. The primary method of grapevine virus control is prevention by biological indexing and molecular- and serological screening of rootstocks and scions before propagation. Due to the spread of grapevine viruses through insect vectors, and in the case of GRSPaV the absence of serological screening, these methods of virus control are not always effective. In the past several methods, from cross-protection to pathogen derived resistance (PDR), have been applied to induce plant virus resistance, but with inconsistent results. In recent years the application of post-transcriptional gene silencing (PTGS), a naturally occurring plant defense mechanism, to induce targeted virus resistance has achieved great success. The Waterhouse research group has designed plant transformation vectors that facilitate specific virus resistance through PTGS. The primary focus of this study was the production of virus specific transformation vectors for the introduction of grapevine virus resistance. The Waterhouse system has been successfully utilised for the construction of three transformation vectors with the pHannibal vector as backbone. Each vector contains homologous virus coat protein (CP) gene segments, cloned in a complementary conformation upstream and downstream of an intron sequence. The primary vector (pHann-SAScon) contains complementary CP gene segments of both GRSPaV and GLRaV-3 and was designed for the introduction of multiple-virus resistance. For the construction of the primary vector the GRSPaV CP gene was isolated from RSP infected grapevines. A clone of the GLRaV-3 CP gene was acquired. The second vector (pHann- LR3CPsas) contains complementary CP gene segments of GLRaV-3. The third vector (pHann-LR2CPsas) contains complementary CP gene segments of GLRaV-2. The cassette containing the complementary CP gene segments of both GRSPaV and GLRaV-3 was cloned into pART27 (pART27-HSAScon), and used to transform N tabacum cv. Petit Havana (SRI), through A. tumefaciens mediated transformation. Unfortunately potential transformants failed to regenerate on rooting media; hence no molecular tests were performed to confirm transformation. Once successful transformants are generated, infection with a recombinant virus vector (consisting of PYX, the GFP gene as screenable marker and the complementary CP gene segments of both GRSPaV and GLRaV-3) will be used to test for the efficacy of the vectors to induce resistance. A secondary aim was added to this project when a need was identified within the South African viticulture industry for GRSPaV specific antibodies to be used in serological screening. To facilitate future serological detection of GRSPaV, the CP gene was isolated and expressed with a bacterial expression system (pETI4b) within the E. coli BL2I(DE3)pLysS cell line. The expressed protein will be used to generate GRSPaV CP specific antibodies.
AFRIKAANSE OPSOMMING: Virusse is van die belangrikste patogene by wingerd. Daar bestaan geen effektiewe chemiese beheer nie, en geen wingerd- of ander natuurlike weerstandsgene teen wingerdvirusse is al ontdek nie. Die primêre metode van beheer t.o.v. wingerdvirusse is voorkoming deur biologiese indeksering, en molekulêre- en serologiese toetsing van onderstokke en entlote voor verspreiding. As gevolg van die verspreiding van wingerdvirusse deur insekvektore, en in die geval van GRSPa V die tekort aan serologiese toetsing, is dié metodes van virusbeheer nie altyd effektief nie. In die verlede is metodes soos kruis-beskerming en patogeen-afgeleide weerstand (PDR) gebruik om virusweerstand te induseer, maar met inkonsekwente resultate. In onlangse jare is post-transkripsionele geenonderdrukking (PTGS), 'n natuurlike plantbeskermingsmeganisme, met groot sukses toegepas om geteikende virusweerstand te induseer. Die Waterhouse-navorsingsgroep het planttransformasievektore ontwerp wat spesifieke virusweerstand induseer d.m.v. PTGS. Die vervaardiging van virus spesifieke tranformasievektore vir die indusering van wingerdvirusweerstand was die primêre doelwit van hierdie studie. Die Waterhouse-sisteem was gebruik vir die konstruksie van drie transformasievektore, met die pHannibal vektor as basis. Elke vektor bevat homoloë virus kapsiedproteïen (CP) geensegmente, gekloneer in 'n komplementêre vorm stroom-op en stroom-af van 'n intronvolgorde. Die primêre vektor (pHann-SAScon) bevat komplementêre CP geensegmente van beide GRSPaV en GLRaV-3, en was ontwerp vir die indusering van veelvoudige-virusweerstand. Die CP-geen van GRSPa V was vanuit RSP-geïnfekteerde wingerd geïsoleer, vir die konstruksie van die primêre vektor. 'n Kloon van die GLRa V-3 CP-geen was verkry. Die tweede vektor (pHann-LR3CPsas) bevat komplementêre CP geensegmente van GLRaV-3. Die derde vektor (pHann-LR2CPsas) bevat komplementêre CP geensegmente van GLRa V-2. Die kasset bestaande uit die komplementêre CP geensegmente van beide GRSPaV en GLRaV-3, was gekloneer in pART27 (pART27-HSAScon), en gebruik om N tabacum cv. Petit Havana (SRI) te transformeer d.m.v. A. tumefaciens bemiddelde transformasie. Ongelukkig het potensiële transformante nie geregenereer op bewortelingsmedia nie; gevolglik was geen molekulêre toetse gedoen om transformasie te bevestig nie. Na suksesvolle transformante gegenereer is, sal infeksie met 'n rekombinante-virusvektor (bestaande uit PYX, die GFP geen as waarneembare merker en die komplementêre CP geensegmente van beide GRSPa V en GLRa V-3) gebruik word om die effektiwiteit van die vektore as weerstandsinduseerders te toets. 'n Sekondêre doelwit is by die projek gevoeg toe 'n behoefte aan GRSPaV spesifieke teenliggame binne die Suid-Afrikaanse wynbedryf geïdentifiseer is, vir gebruik in serologiese toetsing. Om toekomstige serologiese toetsing van GRSPa V te bemiddel, was die CP-geen geïsoleer en in 'n bakteriële uitdrukkingsisteem (PETI4b) uitgedruk, in die E. coli BL21(DE3)pLysS sellyn. Die uitgedrukte proteïne sal gebruik word vir die vervaardiging van GRSPa V CP spesifieke antiliggame.
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Filkowski, Jody, and University of Lethbridge Faculty of Arts and Science. "The effect of pathogens on plant genome stability." Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences, 2004, 2004. http://hdl.handle.net/10133/254.
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Resistance (R) genes, a key factor in determining the resistance of plants, have been shown often to be highly allelic entities existing in duplicated regions of the genome. This characteristic suggests that R-gene acquisition may have arisen through frequent genetic rearrangements as a result of transient, reduced genome stability. Tabacco plants transgenic for a recombination construct exhibited reduced genome stability upon infection with a virulent pathogen (tobacco mosaic virus). The reduced genome stability manifested as an increase in recombination events in the transgene. Such increases were observed following a virulent pathogen attack. This increase in recombination was shown to be systemic and was observed prior to systemic viral movement suggesting the presence of a systemic recombination signal. Further molecular analyses revealed that specific R-gene loci experience a large frequency of rearrangements following a virulent pathogen encounter. The possible targeting of instability to R-gene regions may be controlled through epigenetic processes, in particular, DNA methylation.xiii, 119 leaves ; 29 cm.
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Ramburan, Viresh Premraj. "Genetic mapping of adult plant stripe rust resistance in the wheat cultivar Kariega." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53438.
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Thesis (PhD (Agric)) -- Stellenbosch University, 2003.ENGLISH ABSTRACT: Stripe (yellow) rust of wheat, caused by Puccinia striiformis f.sp. tritici, was first detected as a single introduction into South Africa in 1996. Two additional pathotypes have since been identified. Control of the disease may be achieved by use of genetic adult plant resistance (APR) as is present in the local cultivar 'Kariega'. The aim of this project was to understand the genetic basis of the APR in 'Kariega' to facilitate breeding of new varieties with genetic resistance to stripe rust. A partial linkage map of a 'Kariega X Avocet S' doubled haploid population covering all 21 wheat chromosomes was generated using 208 DNA markers, viz, 62 SSR, 133 AFLP, 3 RGA and 10 SRAP markers, and 4 alternative loci. The different marker techniques detected varying polymorphism, viz, overall SSR: 46%, AFLP: 7%, SRAP: 6% and RGA: 9%, and the markers produced low levels of missing data (4%) and segregation distortion (5%). A significant feature of the linkage map was the low polymorphism found in the D genome, viz, 19% of all mapped DNA markers, 11% of all AFLP markers and 30% of the total genome map distance. A region exhibiting significant segregation distortion was mapped to chromosome 4A and a seedling resistance gene for stem rust (Puccinia graminis f.sp . tritici), Sr26, mapped to chromosome 6A close to three SSR markers. The leaf tip necrosis gene, Ltn, which was also segregating in the population, mapped to chromosome 7D. Protocols for SRAP and RGA were optimised, and SRAP marker use in wheat genetic linkage studies is reported for the first time. The linkage map was used together with growth chamber and replicated field disease scores for QTL mapping. Chromosomes showing statistically significant QTL effects were then targeted with supplementary SSR markers for higher resolution mapping. The quality of disease resistance phenotypic data was confirmed by correlation analysis between the different scorers for reaction type (0.799±0.023) and for transformed percentage leaf area infected (0.942±0.007). Major QTL were consistently identified on chromosome 7D (explaining some 25-48% of the variation) and on chromosome 2B (21-46%) using transformed percentage leaf area infected and transformed reaction type scores (early and final) with interval mapping and modified interval mapping techniques. Both chromosomal regions have previously been identified in other studies and the 7D QTL is thought likely to be the previously mapped APR gene Yr 18. Minor QTL were identified on chromosomes lA and 4A with the QTL on 4A being more prominent at the early field scoring for both score types. A QTL evidently originating from 'Avocet S' was detected under growth chamber conditions but was not detected in the field, suggesting genotype-environment interaction and highlighting the need for modifications of growth chamber conditions to better simulate conditions in the field. The genetic basis of the APR to stripe rust exhibited by 'Kariega' was established by mapping of QTL controlling this trait. The linkage map constructed will be a valuable resource for future genetic studies and provides a facility for mapping other polymorphic traits in the parents of this population with a considerable saving in costs.
AFRIKAANSE OPSOMMING: Streep of geelroes van koring word veroorsaak deur Puccinia striiformis f. sp tritici, en is die eerste keer in 1996 in Suid-Afrika na introduksie van 'n enkele patotipe waargeneem. Twee verdere patotipes is sedertdien in Suid-Afrika gei"dentifiseer. Beheer van die siekte word veral moontlik gemaak deur die gebruik van genetiese volwasseplantweerstand soos gei"dentifiseer in die plaaslike kultivar 'Kariega'. Die doel van hierdie studie was om die genetiese grondslag van die streeproesweerstand te ontrafel ten einde die teling van nuwe bestande kultivars moontlik te maak. 'n Verdubbelde haplo1ede populasie uit die kruising 'Kariega X Avocet S' is aangewend om 'n gedeeltelike koppelingskaart vir die volle stel van 21 koring chromosome saam te stel. Die kaart het uit 208 DNA merkers, nl., 62 SSR, 133 AFLP, 3 RGA, 10 SRAP merkers en 4 ander lokusse bestaan. Totale polimorfisme wat deur die verskillende merkersisteme opgespoor is, was as volg: SSR: 46%, RGA: 9%, AFLP: 7% en SRAP: 6%. Die mate van ontbrekende data was gering (4%) asook die mate van segregasie distorsie (5%) van 'n enkele geval wat op chromosoom 4A gekarteer is. 'n Prominente kenmerk van die koppelingskaart is die relatiewe gebrek aan polimorfiese merkers op die D-genoom, nl., slegs 19% van alle DNA merkers en 11% van alle AFLP merkers wat slegs 30% van die totale genoom kaartafstand bestaan het. Die stamroes (Puccinia graminis f. sp. tritici) saailingweerstandsgeen, Sr26, karteer op chromosoom 6A naby drie SSR merkers. Die geen vir blaartipnekrose, Ltn, karteer op chromosoom 7D. Protokolle vir SRAP en RGA merkers is ge-optimiseer en gebruik van SRAP merkers in koppelings-analise word vir die eerste keer in koring gerapporteer. Die koppelingskaart is in kombinasie met groeikamerdata en gerepliseerde veldproefdata gebruik om die gene (QTL) vir volwasseplant streeproesweerstand te karteer. Chromosome met statisties betekenisvolle QTL is met aanvullende SSR merkers geteiken om die resolusie van kartering verder te verhoog. Die kwaliteit van fenotipiese data, soos in die proewe aangeteken, is bevestig deur korrelasies te bereken tussen lesings geneem deur onafhanklike plantpataloe (0.799 ± 0.023 vir reaksietipe en 0.942 ± 0.007 vir getransformeerde persentasie blaaroppervlakte besmet). Hoofeffek QTL vir die twee maatstawwe van weerstand is deur middel van die metodes van interval QTL kartering en gemodifiseerde interval QTL kartering konsekwent op chromosome 7D (25-48% van variasie verklaar) en 2B (21-46% van variasie verklaar) ge"identifiseer. In vorige studies is aangetoon dat beide chromosome 7D en 2B QTL vir volwasseplant streeproesweerstand dra. Die 7D QTL is waarskynlik die weerstandsgeen, Yr 18. QTL met klein effekte op weerstand is op chromosome lA en 4A ge"identifiseer. Die effek van laasgenoemde geen was meer prominent in die velddata in die vroee datum van weerstandsbeoordeling. Een QTL, afkomstig van 'Avocet S', is slegs onder groeikamertoestande identifiseerbaar. Dit dui op moontlike genotipe-omgewing wisselwerking en beklemtoon die noodsaaklikheid om aanpassings te maak in groeikamertoestande vir beter simulasie van veldproeftoestande. Die genetiese grondslag van volwasseplantweerstand teen streeproes in die kultivar 'Kariega' is deur QTL kartering bepaal. Die 'Kariega X Avocet S' koppelingskaart kan as 'n waardevolle basis dien vir toekomstige genetiese ontledings van ander polimorfiese kenmerke in die populasie.
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Vanstone, Vivien Alison. "The role of fungi and the root lesion nematode, Pratylenchus neglectus, in damaging wheat roots in South Australia." Title page, summary and contents only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phv281.pdf.
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Includes bibliographical references (leaves 265-296). Pathogens associated with root damage were investigated in the Murray Mallee region of South Australia over the 1987-1989 growing seasons. Occurence of fungal species and the root lesion nematode (Pratylenchus neglectus) was assessed, and related to the appearance and severity of symptoms on the roots. Field experiments were supplemented with innoculation tests in the glasshouse and laboratory.
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Hossain, Mohammad Abul. "Powdery mildew on barley : pathogen variability in South Australia : resistance genes in cv. Galleon /." Title page, contents and abstract only, 1986. http://web4.library.adelaide.edu.au/theses/09PH/09phh8287.pdf.
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Taylor, Sharyn Patricia. "The root lesion nematode, Pratylenchus neglectus, in field crops in South Australia." Title page, contents and summary only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09pht2462.pdf.
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Includes bibliographical references (leaves 241-25). Aims to evaluate sampling procedures; assess the extent and magnitude of yield loss caused by Pratylenchus neglectus; assess the population dynamics of Pratylenchus neglectus in cereals; determine whether resistance occurs in field crops; and, assess whether variation occurs between geographically isolated species of Pratylenchus neglectus
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Mazaheri, Lucy. "Development of a Molecular Marker to Track APA G40199 Introgression in Common Bean for Bruchid Resistance." Thesis, North Dakota State University, 2018. https://hdl.handle.net/10365/29300.
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In common bean (Phaseolus vulgaris), the main seed storage pests are the bruchid beetles. Damage done to the seed by the larvae has a large impact on seed quality and yield. Arcelin (ARC), phytohaemagglutinin (PHA), and α-amylase inhibitor (α-AI) are linked seed storage proteins that form the APA locus on chromosome Pv04 and are associated with resistance. A major breeding objective is to introduce bruchid resistance into common bean from a resistant tepary genotype, G40199, by introgressing the resistant APA locus into susceptible common bean backgrounds. Here we developed a molecular marker that tracks the introgression. A set of PCR primers to the α-amylase inhibitor locus amplified a DNA fragment that showed a 45 base pair insertion in the middle of a lectin Leg_b domain. This enhanced locus characterization and insertion/deletion marker may preclude the need for bruchid resistance screening early in the breeding.United States. Agency for International Development
United States. Global Hunger and Food Security Initiative (Cooperative Agreement No. EDH-A-00-07-00005-00)
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Sharma, Sapna. "Genetics of Wheat Domestication and Septoria Nodorum Blotch Susceptibility in Wheat." Thesis, North Dakota State University, 2019. https://hdl.handle.net/10365/29767.
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T. aestivum ssp. spelta Iranian type has long been thought to potentially be the direct non-free threshing hexaploid progenitor. I evaluated a RIL population derived from a cross between CS and Iranian spelta accession P503 to identify loci suppressing free-threshabilty in P503. Identification of QTL associated with threshability in region known to harbor the Tg2A gene, and an inactive tg2D allele supported the hypothesis of Iranian spelta being derived from a more recent hybridization between free-threshing hexaploid and emmer wheat. Parastagonospora nodorum is an important fungal pathogen and secretes necrotrophic effectors that evoke cell death. In this research, a DH population segregating for Snn5 was used to saturate Snn5 region of chromosome 4B with molecular markers. The physical distance between Snn5 flanking markers was narrowed to 1.38 Mb with genetic distance of 2.8 cM. The markers developed in this study will provide a strong foundation for map-based cloning of Snn5.
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Du, Min. "A greenhouse screening method for resistance to gray leaf spot in maize." Thesis, Virginia Tech, 1993. http://hdl.handle.net/10919/42953.
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Martin, Pierre. "Genetic studies on resistance to alfalfa mosaic virus (AMV) and tolerance to white clover mosaic virus (WCMV) in red clover (Trifolium pratense L.)." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61820.
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Christians, Gillian Eleanore. "Identification of molecular markers linked to woolly apple aphid (Eriosoma lanigerum) (Hausmann) resistance in apple." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53454.
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Thesis (MSc)--Stellenbosch University, 2003.ENGLISH ABSTRACT: Apple (Malus x domestica Borkh.) is an important horticultural crop worldwide and in the Western Cape. The income generated from apple and other deciduous fruit production amounts to approximately 25% of the gross total value of horticultural production in the Western Cape. Unfortunately diseases and pests adversely affect fruit production in this region. Woolly apple aphids (Eriosoma lanigerum L. (Hausmann» have a significant effect on the apple industry in the Western Cape. Damage caused is two-fold, occurring aerially and terrestrially. Insects colonise the plants, feeding off the phloem sap. Aphid infestation around the root system results in repeated infestation of the foliage as it serves as a reservoir of aphids. In extreme cases, the apple cores are also infested, thus affecting the sale of apples. In 1962, Northern Spy was identified as a woolly apple aphid resistant rootstock and has since then formed the basis for traditional rootstock breeding programmes. The Er1 gene in Northern Spy confers resistance. According to one report, the natural resistance of Northern Spy was overcome in South Africa in 1968, but this was not confirmed in an independent study. The main objectives of this study was to firstly identify molecular markers more closely linked to the woolly apple aphid resistance gene, Er1, than existing markers, by applying AFLP technology to selected seedlings, identified to be resistant by conventional phenotyping. If identified, these markers can be incorporated into existing breeding programmes. Secondly, previously identified RAPD and SCAR markers were tested to determine their applicability in local populations for use in breeding programmes. Ultimately the segregation of the Er1 gene in South African populations can be determined if tightly linked markers are identified. Three families were derived from crosses of each of three resistant genotypes, namely Northern Spy, Rootstock 5 and Russian Seedling and a susceptible cultivar, Braeburn. For the three successive years of the study, each resistant genotype was allowed to cross-pollinate in isolation with the susceptible parent. Two hand-pollinated families, Russian Seedling x Liberty and Russian Seedling x Northern Spy, were also included in the study. The amplified fragment length polymorphism (AFLP) technique was used in an attempt to identify markers in the resistant and susceptible seedlings. No markers were identified using this technique. Known sequence characterised amplified regions (SCAR) and random amplified polymorphic DNA (RAPD) markers were used due to their suitability in marker-assisted selection for woolly apple aphid resistance. Varying results were obtained with these markers and no conclusive information was acquired with regard to the segregation of the Er] gene in any of these rootstocks and crosses. This underlines the need for the development of markers that can readily be applied in local breeding programmes. The identification and integration of such markers will greatly benefit the local and world wide apple industries.
AFRIKAANSE OPSOMMING: Appels (Malus x domestica Borkh.) is wêreldwyd en in die Wes-Kaap 'n belangrike landbougewas. Inkomste gegenereer deur appels en ander sagtevrugte vorm bykans 25% van die bruto inkomste uit vrugte in die Wes-Kaap. Siektes en insekpeste verlaag egter die produksie van vrugte in hierdie streek. Appelbloedluise (Eriosoma lanigerum L. (Hausmann» het 'n groot invloed op appelproduksie in die Wes-Kaap. Skade word bogronds en ondergronds aangerig. Insekte koloniseer die plant en leef op floeëmsap. Besmetting van die wortels lei tot herhaalde besmetting van bogrondse dele aangesien die insekte aanteelop die wortels. In uiterste gevalle word die vrugte geaffekteer, wat vrug-verkope beïnvloed. 'Northern Spy' is in 1962 geïdentifiseer as 'n onderstam met natuurlike weerstand teen appelbloedluis en het vir lank die basis gevorm vir tradisionele telingsprogramme. Weerstand word verleen deur die Erf geen. Volgens een verslag is die natuurlike weerstand van Northern Spy egter in 1968 in Suid-Afrika oorkom, maar dit is nog nie in 'n onafhanklike studie bevestig word nie. Die hoof doelstellings van hierdie studie was om eerstens deur middel van die AFLP tegniek molekulêre merkers te identifiseer wat nouer gekoppel is aan die appelbloedluis weerstandsgeen, En, as bestaande merkers. Hierdie tegniek is toegepas op saailinge wat deur konvensionele fenotipering geselekteer is. Indien merkers suksesvol geïdentifiseer is, kan dit in bestaande telingsprogramme geïntegreer word. Tweedens is bestaande RAPD en SCAR merkers ook getoets om hul toepaslikheid te bepaal vir gebruik in plaaslike teelprogramme. Oplaas sal die segregasie van die Erf geen in Suid- Afrikaanse populasies ook deur middel van nou gekoppelde merkers bepaal kan word. Kruisings van elk van die drie weerstandbiedende genotipes, naamlik 'Northern Spy', 'Rootstock 5' en 'Russian Seedling', en die vatbare kultivar, 'Braeburn' , het drie families daargestel. Elke weerstandbiedende genotipe is toegelaat om in isolasie te kruisbestuif met die vatbare ouer. Twee hand-bestuifde families, 'Russian Seedling' x 'Liberty' en 'Russian Seedling' x 'Northern Spy', is in 'n latere stadium van die studie ingesluit. Die AFLP tegniek is gebruik vir die identifikasie van polimorfiese merkers tussen vatbare en weerstandbiedende populasies. Geen merkers is egter geïdentifiseer nie. Bestaande SCAR en RAPD merkers is vervolgens gebruik om te bepaal of hulle geskik is vir gebruik in merker-bemiddelde seleksie vir appelbloedluis weerstand. Wisselende resultate is verkry ten opsigte van amplifikasie, herhaalbaarheid van resultate was swak en geen onweerlegbare bewyse oor die segregasie van die Erfgeen is bekom nie. Dit beklemtoon die noodsaaklikheid om merkers wat geredelik in plaaslike teelprogramme toegepas kan word, te ontwikkel. Die identifikasie en integrasie van sulke merkers sal die plaaslike en wêreld-wye appel industrieë aansienlik bevoordeel.
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Hutchinson, Chad M. "Agrobacterium tumefaciens mediated transformation of orchid tissue with the sense and antisense coat protein genes from the odontoglossum ringspot virus." Virtual Press, 1992. http://liblink.bsu.edu/uhtbin/catkey/834608.
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This research was an attempt to use a dicot transformation vector to transform a monocot. The initial purpose of this thesis was to transform orchids with the sense and antisense coat protein genes from the Odontoglossum ringspot virus (ORSV) in an effort to mitigate viral symptoms in transgenic plants using the transformation vector, Agrobacterium tumefaciens. However, it soon became apparent that much time would be needed to develop a transformation protocol. The transformation vectors used included the Agrobacterium tumefaciens disarmed strain LBA4404 with the binary plasmid pB1121, the disarmed strain At699 with the binary plasmid pCNL65, and the wild-type strain Chry5. The marker gene on the binary plasmids of both disarmed strains was p-glucuronidase (GUS).Several transformation protocols were used in an effort to determine if this transformation system would work on orchids. Transformation was not achieved even though a number of experimental conditions were varied. These included using two different types of orchid tissue, callus and protocorms; using two different species of orchids, Cattleya Chocolate Drop x Cattleytonia Kieth Roth and Cymbidium maudidum; varying the time the plant tissue was exposed to the bacteria from 1 hour to 96 hours; performing experiments with and without the wound signal molecule acetosyringone; and exposing the tissue to the virulent strains of A. tumefaciens mentioned previously.This research also developed GUS assay conditions necessary to decrease the number of false positives due to bacterial contamination. These conditions included chloramphenicol in the GUS assay buffer.Department of Biology
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Parsons, Stephen H. "Comparing orchid transformation using agrobacterium tumefaciens and particle bombardment." Virtual Press, 1995. http://liblink.bsu.edu/uhtbin/catkey/941350.
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The Wheeler Orchid Collection is home to some of the most endangered species of orchids in the world. This fantastic reservoir of endangered species has been enhanced and broadened by its function as a plant rescue station for the U.S. customs service. Unfortunately, this responsibility increases the risk of bringing orchids, which harbor contageous diseases, into the greenhouse where sap transmitted diseases such as the Tobacco Mosaic Virus (TMV), can run rampant. Although manipulation of orchid characteristics is typically done by classical plant breeding techniques, genetic engineering is emerging as a useful technique for the introduction of desirable traits into the orchid genome. Through the use of genetic engineering techniques it may be possible to mitigate the symptoms associated with this destructive virus. Virus resistance may be achieved through the expression of either the sense or antisense viral coat protein gene in orchid tissues if an efficient means of orchid transformation is developed. In this research two transformation protocols were examined for their ability to efficiently transform orchid tissue. The first transformation protocol explored utilized the native ability of Aq bacterium tumefaciens to incorporate DNA into host plants to achieve transformation. The second mechanism explored was particle bombardment transformation.Many strains of A. tumefaciens were employed using direct exposure of Cattleya_ orchid protocorm and callus tissue. Particle bombardment using DNA coated 0.5 um diameter tungsten particles and high pressure helium tank acceleration was employed. The particle bombardment procedure employed the pG35barB plasmid which confers herbicide resistance to the herbicide basta when integrated and expressed in plant tissues.GUS fluorescence assays and PCR analysis indicate that T-DNA is present in orchid tissues, while Southern blot analysis was unable to display that integration had occurred. Particle bombardment yielded herbicide resistant orchid tissues which have yet to be analyzed by Southern blot analysis to confirm integration due to limited tissue quantities.Department of Biology
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Presello, Daniel A. "Studies on breeding of maize for resistance to ear rots caused by Fusarium spp. and on the occurrence of viruses in maize in eastern Canada." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38260.
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Responses from pedigree selection for resistance to gibberella ear rot were assessed in four maize (Zea mays L.) populations, two selected after inoculation of Fusarium graminearum (Schwabe) macroconidia into the silk channel and two selected after inoculation into developing kernels. Responses were significant in both populations selected for silk resistance and in one of the populations selected for kernel resistance. Selection was more effective in later generations and genetic gains were associated with among-family selection but not with within-family selection. Results obtained here indicate that responses to selection could be more efficiently obtained by applying high selection intensities in advanced generations, by managing earlier generations as bulks and by reducing the number of plants per family. In another experiment, a wide sample of Argentine maize germplasm was evaluated for silk and kernel resistance to gibberella ear rot and to fusarium ear rot (caused by F. verticillioides (Saccardo) Nirenberg [=F. moniliforme (Sheldon)]. Several entries exhibited disease resistance in comparison with local check hybrids, particularly for fusarium ear rot, the most prevalent ear rot in Argentina. Results obtained in this study suggested the presence of general mechanisms controlling silk and kernel resistance to both diseases. In a supplementary study, viral diseases were surveyed in maize fields from the provinces of Ontario and Quebec in 1999 and 2000. Barley yellow dwarf was found in 1999. Sugarcane mosaic, maize dwarf mosaic and wheat streak mosaic were found in 2000. These diseases were not important for grain-maize planted in May, the most prevalent kind of maize crop in these provinces. Some of these diseases, such as sugarcane maize mosaic and maize dwarf mosaic were found important only in maize fields planted during or after the month of June, and this is of commercial relevance only for sweet corn.
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Eksteen, Aletta. "Ontwikkeling van molekulere merkers vir wilde-spesie-verhaalde weerstandsgeenkomplekse van gewone koring." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2087.
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Thesis (MSc (Genetics))--University of Stellenbosch, 2009.Worldwide, the rust diseases cause significant annual wheat yield losses (Wallwork 1992; Chrispeels & Sadava 1994). The utilization of host plant resistance to reduce such losses is of great importance particularly because biological control avoids the negative environmental impact of agricultural chemicals (Dedryver et al. 1996). The wild relatives of wheat are a ready source of genes for resistance to disease and insect pests. A large degree of gene synteny still exists among wheat and its wild relatives (Newbury & Paterson 2003). It is therefore possible to transfer a chromosome segment containing useful genes to a homologous region in the recipient genome without serious disruption of genetic information. Special cytogenetic techniques are employed to transfer genes from the wild relatives to the wheat genomes (Knott 1989). Unfortunately the transfer of useful genes may be accompanied by the simultaneous transfer of undesirable genes or redundant species chromatin which has to be mapped and removed (Feuillet et al. 2007). DNA markers are extremely useful for the characterisation and shortening of introgressed regions containing genes of interest (Ranade et al. 2001), and may also be used for marker aided selection of the resistance when the genes are employed commercially. Eight wheat lines containing translocations/introgressions of wild species-derived resistance genes were developed by the Department of Genetics (SU). These lines are presently being characterized and mapped and attempts are also being made to shorten the respective translocations. This study aimed to find DNA markers for the various translocations and to convert these into more reliable SCAR markers that can be used in continued attempts to characterize and improve the respective resistance sources. A total of 260 RAPD and 21 RGAP primers were used to screen the eight translocations and, with the exception of Lr19, it was possible to identify polymorpic bands associated with each translocation. However, it was not possible to convert all of these into more reliable SCAR markers. The primary reason for this was the low repeatability of most of the bands. Certain marker fragments turned out to be repeatable but could not be converted successfully. Some of the latter can, however, be used directly (in RAPD or RGAP reactions) as markers. The Lr19 translocation used in the study (Lr19-149-299) is a significantly reduced version of the original translocation and failure to identify polymorphisms associated with it can probably be ascribed to its small size. The following numbers of markers (direct and converted into SCARs) were Worldwide, the rust diseases cause significant annual wheat yield losses (Wallwork 1992; Chrispeels & Sadava 1994). The utilization of host plant resistance to reduce such losses is of great importance particularly because biological control avoids the negative environmental impact of agricultural chemicals (Dedryver et al. 1996). The wild relatives of wheat are a ready source of genes for resistance to disease and insect pests. A large degree of gene synteny still exists among wheat and its wild relatives (Newbury & Paterson 2003). It is therefore possible to transfer a chromosome segment containing useful genes to a homologous region in the recipient genome without serious disruption of genetic information. Special cytogenetic techniques are employed to transfer genes from the wild relatives to the wheat genomes (Knott 1989). Unfortunately the transfer of useful genes may be accompanied by the simultaneous transfer of undesirable genes or redundant species chromatin which has to be mapped and removed (Feuillet et al. 2007). DNA markers are extremely useful for the characterisation and shortening of introgressed regions containing genes of interest (Ranade et al. 2001), and may also be used for marker aided selection of the resistance when the genes are employed commercially. Eight wheat lines containing translocations/introgressions of wild species-derived resistance genes were developed by the Department of Genetics (SU). These lines are presently being characterized and mapped and attempts are also being made to shorten the respective translocations. This study aimed to find DNA markers for the various translocations and to convert these into more reliable SCAR markers that can be used in continued attempts to characterize and improve the respective resistance sources. A total of 260 RAPD and 21 RGAP primers were used to screen the eight translocations and, with the exception of Lr19, it was possible to identify polymorpic bands associated with each translocation. However, it was not possible to convert all of these into more reliable SCAR markers. The primary reason for this was the low repeatability of most of the bands. Certain marker fragments turned out to be repeatable but could not be converted successfully. Some of the latter can, however, be used directly (in RAPD or RGAP reactions) as markers. The Lr19 translocation used in the study (Lr19-149-299) is a significantly reduced version of the original translocation and failure to identify polymorphisms associated with it can probably be ascribed to its small size. The following numbers of markers (direct and converted into SCARs) were v identified: S8-introgression (Triticum dicoccoides) = one RAPD and two SCARs; S13-translocation (Aegilops speltoides) = four RAPDs, three RGAPs and five SCARs; S15-translocation (Ae. peregrina) = one RAPD and two SCARs; S20-translocation (Ae. neglecta) = two RAPDs, two RGAPs and one SCAR. The markers are already being employed in current projects aiming to map and shorten these translocations. Some of the markers can be combined in multiplex reactions for more effective mass screening. No repeatable markers could be identified for the four remaining translocations (S12 from Ae. sharonensis; S14 from Ae. kotschyi; Smac from Ae. biuncialis and Lr19-149-299 from Thinopyrum ponticum).
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Becker, John van Wyk. "Plant defence genes expressed in tobacco and yeast." Thesis, Stellenbosch : University of Stellenbosch, 2002. http://hdl.handle.net/10019/2924.
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Bowen, C. Roger. "Iron deficiency chlorosis in sorghum." 1985. http://hdl.handle.net/2097/27399.
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Kulyingyong, Sunan. "In vitro activity of sorghum non-tannin polyphenols on growth of potential mycotoxin-producing fungi." 1986. http://hdl.handle.net/2097/22098.
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Robert, Olupot John. "Genetic analysis of Striga hermonthica resistance in Sorghum (Sorghum bicolor) genotypes in Eastern Uganda." Thesis, 2011. http://hdl.handle.net/10413/9981.
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Sorghum (Sorghum bicolor) is the third most important cereal food crop in Uganda. However,
the parasitic weed Striga hermonthica severely constraints its production. The use of Striga
resistant sorghum varieties may be one of the most feasible ways of managing the Striga
problem. A series of studies were carried out with the overall objective to develop new sorghum
genotypes that are resistant to Striga and high yielding in Eastern Uganda. Initially, a
participatory rural appraisal (PRA) was carried out with the main objectives to study the current
constraints faced by farmers in sorghum production and determine their preferences for new
sorghum varieties. Secondly, fifty different African sorghum accessions were evaluated to
determine phenotypic and genotypic variability for Striga resistance and identify suitable parents
to be used in breeding for new Striga resistant and high yielding sorghum genotypes. Thirdly, a
genetics study was conducted to determine gene action responsible for Striga resistance and
sorghum yield in new sorghum genotypes. Finally, laboratory studies were carried out to identify specific mechanisms of Striga resistance available in new sorghum genotypes and their parents.
During the PRA, Striga was identified as the main constraint limiting sorghum production in
Eastern Uganda, followed by insect pests. Farmers indicated preference for red gain sorghum
with erect and compact heads, a plant height of 1.5m and a maturity period of around three
months, as well as Striga resistance and drought tolerance. From farmers’ own assessments,
the individual field surveys and soil seed bank analyses that were carried out, the degree of
Striga infestation in farmers’ fields was found to be high.
Both phenotypic and genotypic factors contributed significantly to the variability observed
among the African sorghum accessions with respect to Striga resistance and sorghum crop
performance indicating that Striga resistance can be improved through selection. However,
techniques that minimise environmental effects need to be employed in order to improve on
heritability. The values for genetic coefficient of variation (GCV) and genetic advance (GA)
indicated that genetic gain for Striga resistance could be achieved by selection based on area
under Striga severity progress curve (AUSVPC), area under Striga number progress curve (AUSNPC) and individual Striga emergence counts. The sorghum accessions SRN39, Brhan, Framida, Gubiye, Wahi, P9407 and N13 were found to be resistant to Striga hermonthica. These accessions consistently showed low AUSNPC, AUSVPC, and individual Striga
emergence, Striga vigour and severity indices. These accessions could be used as sources of
Striga resistance genes when breeding for Striga resistance in sorghum.
In the study to determine gene action responsible for Striga resistance and sorghum yield,
significant genetic variation for Striga resistance and sorghum yield parameters was observed
among the new sorghum genotypes and their parents. The sorghum parental lines: Brhan,
SRN39, Hakika and Sekedo consistently had negative GCA effects for AUSNPC and AUSVPC,
while SRN39 and Hakika additionally had negative GCA effects for Striga vigour, indicating that
they were effective in transferring Striga resistance into their progeny. The new genotypes:
SRS1608, SRS3408, SRS2408, SRS4609, SRS3108, SRS2908, SRS2609, SRS609 and SRS1708 had negative SCA effects for AUSNPC, AUSVPC and Striga vigour meaning that they
were resistant to Striga. Sorghum parental lines: Sekedo, Brhan, Framida and Hakika had
positive GCA effects for head length, meaning that they increased head length in their crosses.
The genotypes: SRS3408, SRS5309, SRS1608 and SRS2908 derived from the above parents
had the longest heads compared to other progenies, which were on average, 20% longer than
their parents. The genotypes: SRS609, SRS1408, SRS2608 and SRS3408 were the highest
grain yielders and yielded 11-51% better than the highest yielding parent (Sekedo) under the
non Striga environment. The parental lines; Sekedo, Brhan and Framida had positive GCA
effects for grain yield indicating that they could act as sources of genes for grain yield increase.
The genotypes; SRS609, SRS4609 and SRS2908 had large positive SCA effects for grain yield.
The relative contributions of GCA effects to the observed genotypic variances were 80.5%,
43.3%, 65%, 92.6% and 53.2% for AUSNPC, AUSVPC, Striga vigour, sorghum head length and
plant height respectively. This shows that additive gene action was important in controlling
Striga resistance, sorghum head length and plant height in the present sorghum populations.
Laboratory studies aimed at investigating the specific mechanisms of Striga resistance available
in new sorghum genotypes found that two new sorghum genotypes, SRS1608 and SRS1208
expressed both the low germination stimulant character and low haustoria initiation as
mechanisms of resistance to S. hermonthica. The sorghum genotypes, SRS2808 and
SRS1108, and two fixed lines, Brhan and Hakika expressed only the low germination stimulant
character, while the genotypes, SRS608, SRS3408, SRS4109 and SRS2308 expressed only
the low haustoria initiation mechanism. The inheritance patterns of the low germination
stimulant character in the present sorghum genotypes varied. In some genotypes, it appeared to be controlled by a single gene while in others; it appeared to be controlled by more than one gene.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Meehan, Mitchell Elwin. "A comparison of techniques for screening for resistance to the chinch bug, Blissus leucopterus leucopterus (Say), in sorghum." 1985. http://hdl.handle.net/2097/27497.
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Ndung'u, David Kamundia. "Mutagenesis and development of herbicide resistance in sorghum for protection against Striga." Thesis, 2009. http://hdl.handle.net/10413/670.
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Teshome, Rebeka Gebretsadik. "Integrating sorghum [sorghum bicolor (L.) Moench) breeding and biological control using fusarium oxysporum against striga hermonthica in Ethiopia." Thesis, 2013. http://hdl.handle.net/10413/10752.
Full textAbstract:
Sorghum [Sorghum bicolor (L.) Moench] is a major food security crop for millions of people in sub-Saharan Africa and the fourth most important crop in Africa. The potential sorghum yields are limited due to a number of abiotic, biotic and socio-economic constraints. Among the biotic stresses is the parasitic weed, Striga hermonthica, which inflicts yield losses ranging from 30-100%. Various control options have been recommended to reduce levels of Striga damage. However, these techniques need to be integrated for effective control and to boost sorghum productivity. A series of experiments was conducted to integrate host resistance improvement and the use of a biological control agent, Fusarium oxysporum f.sp. strigae to control Striga hermonthica. These studies were also focused on improving breeders‟ awareness of the traits that farmers‟ desire, on the assumption that farmers‟ variety preference traits are the missing link in technology development and adoption process for S. hermonthica management.
The objectives of the study were to: 1) determine farmers‟ views on sorghum production opportunities; threats; indigenous knowledge and perceptions; breeding priorities; Striga infestation; and the coping mechanisms of farmers in the north eastern and north western Ethiopia, 2) evaluate sorghum genotypes for compatibility to F. oxysporum inoculation where grown in Striga infested soil in controlled environments, 3) determine field responses of sorghum genotypes and F. oxysporum compatibility for integrated Striga management (ISM), 4) determine the variability present among selected sorghum genotypes exhibiting S. hermonthica resistance, and compatibility with the biological control agent using phenotypic and simple sequence repeat (SSR) markers, 5) identify F. oxysporum compatible sorghum parents and hybrids with high combining ability for grain yield, yield components, and Striga resistance for ISM, and 6) undertake farmers‟ participatory assessment, and identify their preferred traits for sorghum genotypes under ISM, simultaneously with the breeders‟ evaluation.
A participatory rural appraisal (PRA) research was conducted involving 315 farmers in nine districts of three administrative zones within two provinces in Ethiopia. Sorghum landraces were preferred by >85% of participants rather than previously improved released varieties. The participating farmers listed and prioritized their sorghum production constraints. In the North Shewa and North Wello zones drought was the most important constraint, followed by Striga. In the Metekel zone Striga was the number one constraint followed by a lack of genotypes with high grain quality.
Controlled environment experiments were conducted involving greenhouse and laboratory tests in order to evaluate 50 sorghum genotypes for their compatibility with F. oxysporum and for possible deployment of the bio-control agent to control Striga. Striga population was reduced by 92% through the application of F. oxysporum, resulting in yield increment of 144%. Twelve sorghum genotypes were identified as promising parents for breeding and to control Striga through integration of host resistance and F. oxysporum seed treatment. During field and sick plot plot evaluations differential responses to F. oxysporum application among the sorghum genotypes were observed for various attributes including Striga plant height. Most traits showed highly significant (p<0.001) genotype X site interactions. Similarly, the main effects of F.oxysporum application were highly significant (p<0.001) across sites for most of the traits. The genotype and genotype X environment biplot identified 13 genotypes that consistently performed well following Fusarium application.
The variability present among 14 selected sorghum genotypes exhibiting S. hermonthica resistance, and compatibility with a biological control agent, Fusarium oxysporum, were determined using phenotypic and 20 polymorphic simple sequence repeat (SSR) markers. Highly significant (p<0.001) differences were detected among genotypes for phenotypic traits. Principal component analysis showed three components that accounted for 73.99% of the total variability exhibited among genotypes. Cluster analysis allocated the genotypes into two major groups, one with a further two subgroups based on morphological traits, showing clear demarcations between the genotypes. The SSR markers revealed high levels of polymorphisms among genotypes, with the mean number of alleles per locus being 6.95 and the mean polymorphic information content being 0.80. The observed genetic diversity was relatively wide, with the allele sizes ranging from 203.6-334 bp. The SSR markers allocated genotypes into two distinct clusters close to the phenotypic markers.
Forty sorghum hybrids were developed through a line by tester mating design involving 10 lines selected for their compatibility with F. oxysporum and high agronomic performances and four Striga resistant tester parents. The F1s and their parents were field evaluated with complementary in-vitro tests. Field evaluations were conducted at two locations: Kobo and Shewa Robit in Ethiopia, which are well known for their severe Striga infestation. Significant (p<0.05) general combining ability (GCA) effects were observed among testers and lines at both sites for days to 50% flowering and maturity, plant height, biomass, number of Striga plants and Striga plant height. Furthermore, significant (p<0.05) specific combining ability (SCA) effects were detected for days to 50% flowering, biomass, grain yield and number of Striga plants. From the complementary in-vitro experiment, highly significant variation (p<0.01) was exhibited due to line x tester interaction for maximum Striga germination distance. The study identified paternal parents with high GCA effects including SRN-39 and Birhan and maternals 235761, 2384443, IC9830, 235466, 237289,235763, and 235929 to be useful for breeding for ISM in sorghum. At Kobo, cross 235763 x N-13 and Shewa Robit IC9830 x SRN-39 had significantly negative SCA effects for the numbers of Striga plants. Progenies of these crosses will be selected in the Striga resistance breeding program.
In the participatory sorghum genotypes assessment, farmers were invited to assess and select the genotypes based on their preferences at maturity and harvesting. The standard agronomic traits and Striga parameters relevant for breeding were collected by the breeders. Earliness, Striga resistance, high yield and high grain quality and threshability were the most important farmers‟-preferred traits for sorghum genotypes. Comparative analyses between farmers‟ and breeders‟ evaluations revealed highly significant correlations (p<0.01) except between Striga resistance and Striga damage and pest resistance and insect damage. Repeatability of scoring genotypes among farmers was consistent (>0.80) for all traits except Striga and pest resistance. The prioritized traits through farmers‟ participation are important for further breeding program. Overall, the study established farmers‟ preferred traits, the effectiveness of ISM to boost sorghum productivity, and identified useful parents and crosses for effective sorghum breeding to control Striga in Ethiopia.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Mariote, David. "Response to selection for downy mildew (Peronosclerospora sorghi) and maize streak virus resistance in three quality protein maize populations in Mozambique." Thesis, 2007. http://hdl.handle.net/10413/748.
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Farsi, Mohammad. "Genetic variation for tolerance and resistance to Pratylenchus neglectus / by Mohammed Farsi." 1995. http://hdl.handle.net/2440/18625.
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Bibliography: leaves 318-347.ix, 347 [24] leaves : ill. (some col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
A major problem in the production of agricultural crops including wheat, is the damage caused by destructive plant parasitic nematodes, among these the root lesion nematode (Pratylenchus spp.) The association of P. neglectus with fungi in ceraeal root disease has been reported. Infection is associated with leaf yellowing, which reduces plant photosynthesis and grain yield. In nematode infested soil, well fertilized crops are usually less affected.
Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996?
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Asiedu, Robert. "A study of resistance to cereal cyst nematode (`Heterodera avenae Woll.`) located in the rye genome of triticale / by Robert Asiedu." 1986. http://hdl.handle.net/2440/21224.
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Bibliography: leaves 133-152iv, 152 leaves, [47] leaves of plates : ill. (1 col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, 1987
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Choe, Y. W. (Young Won). "DNA markers for cereal cyst nematode (Heterodera avenae Woll.) resistance gene in barley." 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phc545.pdf.
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March, Timothy. "The genetic basis of barley black point formation." 2008. http://hdl.handle.net/2440/50740.
Full textAbstract:
Black point of barley grain refers to a discolouration of the embryo end of the grain. Historically black point has been proposed to be due to fungal colonisation of the grain. However, Koch’s postulates have yet to be satisfied. The discolouration occurs during grain fill in response to high humidity or rainfall during the grain filling period. In wheat, which is also affected by black point, the discolouration has been proposed to be due to the oxidation of phenolic acids within the grain to form discoloured end products. Within this study, two approaches were investigated in order to understand the proteins and genes associated with this disorder. Firstly, a proteomics approach enabled the identification of individual proteins associated with black point. Two-dimensional gel electrophoresis was used to compare the proteome of the husk and whole grain tissue of mature black pointed and healthy grain. Very little watersoluble protein was extracted from the husk tissue. However, a significantly larger amount of protein was extracted using a salt extraction buffer, indicating the husk proteins were mostly cell wall bound. Due to the effect of residual salt and low protein concentrations these proteins were not conducive to analysis using two-dimensional gel electrophoresis. Further experiments using acid hydrolysis of the husk tissue and subsequent amino acid analysis revealed that the proteins were bound to the husk cell walls via covalent bonds. In contrast, large quantities of protein were obtained from the whole grain samples. This allowed statistically significant comparisons to be made between gels from healthy and black pointed grains. Two proteins were identified as being more abundant in black pointed grains. Mass spectrometry identified these as isoforms of barley grain peroxidase 1 (BP1). In addition, three proteins were identified as being more abundant in healthy grain. Mass spectrometry revealed these to be isoforms of the same protein with sequence similarity to a partial EST sequence from barley. Using 3' RACE the entire coding sequence of the gene was isolated which revealed that it encoded a novel putative late embryogenesis abundant (LEA) protein. Northern blot analysis was performed for BP1 and LEA and showed that gene expression differences could not account for the differences seen in protein quantities. Western blot analysis revealed that the LEA protein was biotinylated in vivo which is consistent with similar LEA proteins from other plant species. To further understand the role of these proteins in black point, antibodies were raised against the two proteins. Subsequent immunolocalisation studies indicated BP1 was present throughout all tissues of the grain whilst LEA was most abundant in the embryo and aleurone tissue. The second major area of investigation within this thesis was to further delineate the previously identified quantitative trait loci (QTL) associated with black point in barley. Previous studies have reported QTL for black point and kernel discolouration in both barley and wheat. Comparison of the published QTL revealed a locus on the short arm of chromosome 2H to be of particular interest. To identify genes underlying this QTL the genomes of barley, wheat and rice were compared. An in silico approach showed that the QTL shared macro-synteny with rice chromosomes 4 and 7. From the rice genome sequence, barley ESTs with sequence similarity were selected. In total, 20 ESTs were selected based on two main criteria: their putative role in black point and also being evenly spread across the region of the QTL length. These QTL were mapped within the Alexis x Sloop double haploid population. This approach revealed that there was some conservation of synteny but also identified clear boundaries where synteny between barley and rice had been lost since divergence. Significantly, the additional markers mapped to this region have enabled the initial black point QTL to be reduced from approximately 30cM to 20cM. In conclusion, this study has added significant knowledge our understanding of the genetics of black point in barley through the use of two approaches. The proteomics approach has aided in understanding the biochemical processes occurring within the grain in response to black point. The comparative genetics approach has aided in understanding the genetic control of an important region of the genome influencing black point susceptibility. Combined, these findings will direct future research endeavours aimed at producing black point resistant barley cultivars.http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1323053
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008
31
Keller, Karen E. "Interactions between pea seed-borne mosaic virus pathotype 1 and Pisum sativum resistance gene sbm-1." Thesis, 1995. http://hdl.handle.net/1957/34654.
Full text
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Kasozi, Lwanga Charles. "Genetic analysis and selection for maize weevil resistance in maize." Thesis, 2013. http://hdl.handle.net/10413/10746.
Full textAbstract:
The maize weevil (Sitophilus zeamais Motschulsky) is one of the most destructive storage insect pest of maize (Zea mays L.) in tropical Africa and worldwide, especially when susceptible varieties are grown. Therefore, grain resistance against the maize weevil should be part of a major component of an integrated maize weevil management strategy. The specific objectives of this study were to: i) determine farmers’ perceptions about weevil resistance in maize cultivars; ii) determine the genotypic variation for maize weevil resistance in eastern and southern Africa maize germplasm lines; iii) study the gene action conditioning weevil resistance in the inbred line populations from eastern and southern Africa maize germplasm and to measure their combining ability for yield and weevil resistance; iv) determine the effectiveness of two cycles of modified S1 recurrent selection in improving a tropical maize population “Longe5” for weevil resistance and agronomic superiority and v) evaluate the effectiveness of the “weevil warehouse techniques” compared to the “laboratory bioassay technique” as methods of maize screening against the maize weevil.
A participatory rural appraisal (PRA) was conducted in three districts between December 2010 and January 2011, to gather information on the maize weevil pest status in Uganda and farmers’ perceptions about improved maize varieties and the major attributes desired in new maize varieties. Over 95% of farmers knew the maize weevil and its pest status, and were reportedly controlling the maize weevil using wood ashes, red pepper and Cupressus sempervirens. The estimated postharvest weight losses attributed to weevil damage was over 20% within a storage period of four months. The most highly ranked attributes desired in the new maize varieties included high grain yield, tolerance to drought and low nitrogen stresses, resistance to field pests and diseases, good storability and resistance to storage pests.
In the search for new sources of weevil resistance, a total of 180 inbred lines from three different geographical areas were screened for weevil resistance using the laboratory bioassay technique. Eight inbred lines (MV21, MV23, MV75, MV102, MV142, MV154, MV157, and MV170) were consistently grouped in the resistant class, and therefore selected as potential donors for weevil resistance in the maize improvement programs. Large significant genetic variations for weevil resistance, and high levels of heritability (89 – 96%) were observed. The results revealed that there was no significant association between maize weevil resistance andgrain yield; suggesting that breeding for maize weevil resistance can be achieved without compromising grain yield.
Eight weevil resistant and two susceptible inbred line parents were crossed in a 10 x 10 full diallel mating design and the resulting 45 experimental hybrids and their reciprocal crosses evaluated for grain yield and secondary traits under four environments, and also to determine the gene action regulating their expression. The F1 hybrid seed, F2 full-sib and F2 half-sib grain generated from the 45 experimental hybrids and their reciprocals under two environments in Namulonge, were evaluated for weevil resistance using F1 weevil progeny emergence, median development period (MDP), Dobie’s index of susceptibility (DIS), and parental weevil mortality as susceptibility parameters. The general combing ability (GCA), specific combining ability (SCA), and reciprocal effects were all significant for grain yield, with SCA accounting for over 80% of the hybrid sum of squares. Inbred line parent MV44 exhibited positive significant GCA for grain yield and thus can be utilized in the development of synthetics and hybrids. Hybrids MV21 x MV13, MV154 x MV44, and MV154 x MV102 and all hybrids between parent MV142 and the rest of the parental lines exhibited positive and significant SCA effects. For the weevil resistance parameters, the general combining ability (GCA), specific combining ability (SCA) and reciprocal effects were all significant for F1 weevil progeny emergence, MDP, and DIS in the three seed categories. The results revealed that weevil resistance was governed by additive gene action, non-additive, and maternal effects. Parents MV170 and MV142 were consistently exhibiting weevil resistance in the three seed categories and thus recommended for future breeding strategies. Furthermore, most of the hybrids generated from parental line M142 were noted to exhibit outstanding performance in terms of grain yield and weevil resistance.
Another study was conducted to determine the effectiveness of two cycles of modified S1 recurrent selection towards the improvement of weevil resistance in a maize population Longe5. Over 540 selfed ears were selected from the source population (C0) and screened for weevil resistance in the laboratory at Namulonge. Based on weevil resistance characteristics, 162 genotypes were selected from C0 and recombined in an isolated field to generate cycle C1. The same procedure was used for generating cycle C2 from cycle C1, but instead 190 weevil resistant C1 genotypes were selected and recombined to form C2. Seed from cycles C1 and C2, together with that from the source population (C0), was used to plant an evaluation trial in three locations, to compare the performance of the three cycles in terms of grain yield and reaction to the major foliar diseases, and also to produce seed for subsequent screening against weevil ii
infestation. A total of 54 seed samples were screened for weevil resistance in a laboratory at Namulonge, in an experiment laid out in a randomized complete block design. A reduction in grain weight loss of 65% was registered in the C2 seed, whereas in C1 seed it was 15%. A similar trend was observed for F1 weevil progeny emergence and grain damage. Grain yield results indicated a yield gain of 19% realized from cycle C2 while a yield gain of 7% was realized from cycle C1. Furthermore, reductions in disease severity of 27%, 10% and 13% were exhibited for Turcicum leaf blight (TLB), grey leaf spot (GLS) and rust disease, respectively in cycle C2. The results indicated that Longe5 can be improved for maize weevil resistance, grain yield, and resistance to foliar diseases through selection. Further recurrent selection cycles would be recommended.
The last study was aimed at evaluating the potential of shelled grain and suspended ear options of the weevil warehouse technique in discriminating maize genotypes into different susceptibility classes, based on genotype response to weevil attack. It involved comparing the effectiveness of the two options under the weevil warehouse technique with the laboratory bioassay technique using grain damage and grain weight loss as the maize grain susceptibility parameters. Fourteen maize genotypes were screened using the weevil warehouse and the laboratory bioassay techniques at Namulonge. On grouping the 14 genotypes into different response classes, high levels of consistency were observed in the three screening techniques. Therefore, the two weevil warehouse screening options being faster and effective in discriminating maize cultivars towards weevil attack, they were found to be better than the laboratory bioassay technique. The minimum evaluation period required to discriminate genotypes by the two weevil warehouse options was two months from the onset of the experiment.
The maize weevil was noted to be an important storage pest constraining maize production in Uganda. The major weevil control measures included proper postharvest handling procedures and use of indigenous technical knowledge. The results also revealed that host plant resistance could significantly reduce grain damage. It was further revealed that grain resistance against the maize weevil could be enhanced through hybridization and recurrent selection; thus the germplasm identified in the study can provide new sources of maize weevil resistance for commercial deployment and further breeding.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
33
"Disease resistance related genes co-regulated in bacterial leaf blight near isogenic lines, Xa2, Xa12 and Xa14." 2004. http://library.cuhk.edu.hk/record=b5891981.
Full textAbstract:
Shuk-man Chow.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references (leaves 171-186).
Abstracts in English and Chinese.
Thesis committee --- p.i
Statement --- p.ii
Abstract --- p.iii
Acknowledgement --- p.viii
General abbreviations --- p.x
Abbreviations of chemicals --- p.xi
List of figures --- p.xii
List of Tables --- p.xiii
Table of contents --- p.xv
Chapter 1. --- Literature review
Chapter 1.1. --- General introduction to rice disease --- p.1
Chapter 1.1.1. --- Pathogenesis of Bacterial Leaf Blight (BLB) --- p.1
Chapter 1.1.2. --- Pathogenesis of rice blast --- p.2
Chapter 1.1.3. --- Control of rice diseases --- p.3
Chapter 1.2. --- Plant defense mechanisms --- p.4
Chapter 1.2.1. --- Basal resistance in plants --- p.4
Chapter 1.2.2. --- Wound induced defense response --- p.5
Chapter 1.2.3. --- Pathogen induced host defense response --- p.6
Chapter 1.3. --- Structure of R gene products --- p.7
Chapter 1.4. --- Recognition between R and Avr proteins in rice --- p.8
Chapter 1.5 --- Current knowledge on Xa resistance and AvrXa avirulence protein --- p.9
Chapter 1.6 --- Current knowledge on Pi resistance and AvrPi avirulence protein --- p.10
Chapter 1.7 --- Pathogen induced signal transduction cascade --- p.12
Chapter 1.7.1. --- R gene mediated signal transduction cascade --- p.12
Chapter 1.7.2. --- Signal events of G-protein activation --- p.12
Chapter 1.7.3. --- Signaling events for the accumulation of Ca2+ in cytosol --- p.13
Chapter 1.7.4. --- Signaling events for oxidative burst --- p.14
Chapter 1.7.5. --- MAPK cascade in defense signaling --- p.15
Chapter 1.7.6. --- Transcriptional regulation of disease resistance related genes --- p.16
Chapter 1.7.7. --- Translational regulation of disease resistance related genes --- p.17
Chapter 1.8. --- Defense responses and defense related genes --- p.19
Chapter 1.8.1. --- Pathogenesis related (PR) proteins --- p.20
Chapter 1.8.2. --- Phytoalexins --- p.21
Chapter 1.9. --- Disease resistance related genes common between rice blast and BLB resistance --- p.22
Chapter 1.10. --- SA induced signal transduction pathway in rice --- p.23
Chapter 1.11. --- Important tools facilitating the identification of disease resistance related genes from BLB resistant rice lines --- p.24
Chapter 1.12. --- Hypothesis --- p.26
Chapter 1.13. --- Project objective --- p.26
Chapter 2. --- Materials and Methods --- p.27
Chapter 2.1. --- Plant Materials --- p.27
Chapter 2.2. --- Pathogen Inoculation --- p.27
Chapter 2.3. --- RNA extraction --- p.29
Chapter 2.4. --- Denaturing gel electrophoresis --- p.29
Chapter 2.5. --- Subtraction libraries construction --- p.30
Chapter 2.5.1. --- Cloning of disease resistance related genes --- p.32
Chapter 2.5.1.1. --- pBluescript II KS (+) T-vector preparation --- p.32
Chapter 2.5.1.2. --- Ligation --- p.32
Chapter 2.5.1.3. --- Transformation --- p.32
Chapter 2.5.1.4. --- Colony picking --- p.33
Chapter 2.5.1.5. --- PCR amplification of DNA inserts --- p.33
Chapter 2.5.1.6. --- Purification of PCR products --- p.34
Chapter 2.6. --- Gene chips printing --- p.34
Chapter 2.7. --- Probes synthesis and gene chips hybridization --- p.35
Chapter 2.8. --- Standard-RNAs synthesis --- p.35
Chapter 2.9. --- Data collection and analysis --- p.36
Chapter 2.10. --- Sequencing --- p.36
Chapter 2.11. --- cDNA synthesis --- p.37
Chapter 2.12. --- RT-PCR --- p.38
Chapter 2.13. --- DNA gel electrophoresis --- p.39
Chapter 3. --- Results --- p.58
Chapter 3.1. --- Construction of BLB gene chips --- p.58
Chapter 3.1.1. --- Preparation of cDNA clones for gene chips construction --- p.58
Chapter 3.1.2. --- Purification of PCR products on microtiter plate --- p.59
Chapter 3.1.3. --- Gene chips construction --- p.59
Chapter 3.1.4. --- DNA immobilization --- p.62
Chapter 3.1.5. --- Probe synthesis --- p.62
Chapter 3.1.6. --- Gene chip analysis --- p.65
Chapter 3.1.6.1. --- Scanning --- p.65
Chapter 3.1.6.2. --- Data analysis --- p.65
Chapter 3.2. --- "Identification of disease resistance related genes commonly regulated by Xa2, Xal2 and Xal4 BLB resistance loci" --- p.70
Chapter 3.2.1. --- "Signal perception, transduction and regulatory elements" --- p.71
Chapter 3.2.1.1. --- Proteins involved in reversible phosphorylation cascade --- p.71
Chapter 3.2.1.2. --- Proteins potentiate signal transduction through specific protein-protein interaction --- p.72
Chapter 3.2.1.3. --- Other signal transduction components --- p.73
Chapter 3.2.2. --- Transcriptional and translational regulatory elements --- p.74
Chapter 3.2.2.1. --- Proteins involved in transcriptional regulation --- p.74
Chapter 3.2.2.2. --- Proteins involved in post-transcriptional regulation --- p.75
Chapter 3.2.2.3. --- Proteins involved in translational regulation --- p.76
Chapter 3.2.3. --- "Oxidative burst, stress, apoptotic related genes" --- p.77
Chapter 3.2.3.1. --- Stress related proteins --- p.77
Chapter 3.2.3.2. --- Proteins involved in induction of oxidative burst --- p.78
Chapter 3.2.3.3. --- PR proteins --- p.79
Chapter 3.2.3.4. --- Proteolysis related proteins --- p.79
Chapter 3.2.4. --- Cell maintenance and metabolic genes --- p.80
Chapter 3.2.4.1. --- Antioxidant --- p.80
Chapter 3.2.4.2. --- Metabolic genes --- p.81
Chapter 3.2.4.3. --- Molecular chaperone --- p.82
Chapter 3.2.4.4. --- Cell cycle regulators --- p.82
Chapter 3.2.4.5. --- Cell wall maintenance --- p.83
Chapter 3.2.4.6. --- Proteins involved in protein transport --- p.83
Chapter 3.2.5. --- Unclassified/others --- p.84
Chapter 3.3. --- Expression analysis of disease resistance related genes --- p.88
Chapter 4. --- Discussion --- p.141
Chapter 4.1. --- Differential expression of disease resistance candidates --- p.141
Chapter 4.2. --- Disease resistance signal transduction components --- p.143
Chapter 4.2.1. --- Reversible phosphorylation cascade --- p.143
Chapter 4.2.2. --- Signal transduction potentiated by protein-protein interaction --- p.144
Chapter 4.3. --- Other signaling molecules --- p.145
Chapter 4.3.1. --- PRL1-interacting factor G --- p.145
Chapter 4.3.2. --- Vacuolar-type H+-ATPasen subunit G --- p.146
Chapter 4.4. --- Regulation of expression of disease resistance candidates --- p.146
Chapter 4.4.1. --- Transcriptional regulation of disease resistance related genes --- p.146
Chapter 4.4.1.1. --- G-box binding protein --- p.147
Chapter 4.4.1.2. --- MYB TF --- p.147
Chapter 4.4.2. --- Post-transcriptional modification of disease resistance candidates --- p.148
Chapter 4.4.2.1. --- RNA splicing factor --- p.148
Chapter 4.4.2.2. --- Glycine rich RNA binding proteins --- p.149
Chapter 4.4.3. --- Translational regulation of disease resistance related genes --- p.149
Chapter 4.5. --- Induction of oxidative burst --- p.150
Chapter 4.6. --- PR proteins --- p.151
Chapter 4.7. --- Cell maintenance --- p.152
Chapter 4.7.1. --- Protein folding --- p.152
Chapter 4.7.2. --- Protein degradation --- p.153
Chapter 4.7.3. --- ROS scavenging --- p.154
Chapter 4.7.4. --- Regulation of cell cycle --- p.154
Chapter 4.8. --- "Confirmation and profiling of disease resistance related candidates commonly regulated in Xa2, Xal2 and Xal4 BLB resistance NILs at different time points" --- p.155
Chapter 4.8.1. --- Basal resistance related genes --- p.156
Chapter 4.8.2. --- General disease resistance related genes --- p.161
Chapter 4.8.3. --- Pathogen responsive genes --- p.164
Chapter 4.8.4. --- Prediction of novel genes functions --- p.168
Chapter 4.9. --- Future prospect --- p.169
Chapter 4.10. --- Conclusion --- p.169
References --- p.171
Appendix --- p.187
34
McWilliams, Michael G. "Port-Orford-cedar and Phytophthora lateralis : grafting and heritability of resistance in the host, and variation in the pathogen." Thesis, 2000. http://hdl.handle.net/1957/32598.
Full textAbstract:
Port-Orford-cedar (Chamaecyparis lawsoniana) is a forest tree native to
a small area of Oregon and California. A root disease caused by
Phytophthora lateralis causes widespread mortality of Port-Orford-cedar.
This dissertation examines three important elements of the Port-Orford-cedar
P. lateralis pathosystem related to breeding for disease resistance:
use of resistant rootstocks to maintain genotypes of Port-Orford-cedar for
breeding; the heritability and genetic basis of disease resistance; and
variability in virulence and DNA fingerprint among a sample of P. lateralis
isolates.
Port-Orford-cedar was reciprocally grafted to western redcedar (Thuja
plicata), incense cedar (Calocedrus decurrens), and Alaska yellow-cedar
(Chamaecyparis nootkatensis). Port-Orford-cedar scion graft success was
moderate with western redcedar and incense cedar, but extreme
overgrowth of the rootstock by the scion indicated incompatibility. Xylem
union was good, but phloem union was incomplete or lacking. Nearly all
Port-Orford-cedar rootstocks and seedlings exposed to P. lateralis died of
root disease. Four percent of the Alaska yellow-cedar exposed also died,
confirming this tree as a host for P. lateralis.
Resistance of Port-Orford-cedar to P. lateralis is rare. A small number
of trees have been identified exhibiting resistance. A number of families
were tested to determine the genetic basis for resistance. Estimates of
narrow-sense and family mean heritability of resistance, as exhibited by
restriction of lesion length after inoculation, were determined. Both narrow-sense
and family mean heritabilities were between 0.61 and 0.98 in most
tests. Between 21% and 32% of the variance was due to differences
among families.
Thirteen isolates of P. lateralis were collected from three hosts
throughout the geographic range of the fungus. Variation in growth rate on
artificial media at three temperatures, virulence when used to inoculate
Port-Orford-cedar, and DNA fingerprint were compared. There were
significant differences in growth rate among isolates at 24C, but fewer
differences at lower temperatures and on a rich medium. One isolate
produced significantly shorter lesions in three different inoculation tests.
Isolates differed at only two of 189 bands produced by Inter Simple
Sequence Repeat (ISSR) DNA primers, indicating very little genetic
variation among isolates.Graduation date: 2001
35
Gilbert, Brian M. "Characterization of the response mediated by the plant disease susceptibility gene LOV1." Thesis, 2012. http://hdl.handle.net/1957/34284.
Full textAbstract:
Victoria blight, caused by fungus Cochliobolus victoriae, is a disease originally described on oats and recapitulated on Arabidopsis. Victoria blight is used as a model plant disease that conforms to an inverse gene-for-gene interaction. C. victoriae virulence is dependent upon its production of victorin, a host-specific toxin that induces programmed cell death in sensitive plants. In oats, victorin sensitivity and disease susceptibility is conferred by the Vb gene, which is genetically inseparable from the Pc-2 crown rust resistance gene. In Arabidopsis, victorin sensitivity and disease susceptibility is conferred by the LOCUS ORCHESTRATING VICTORIN EFFECTS 1 (LOV1) gene which encodes a NB-LRR protein, a type of protein commonly associated with disease resistance. LOV1-mediated cell death occurs when victorin binds Thioredoxin-h5 (TRX-h5) and LOV1 appears to "guards" TRX-h5. Together, these results suggest C. victoriae causes disease by inducing a resistance response.
The work presented here aimed to determine if the response mediated by LOV1 is functionally related to a resistance response. We genetically characterized the response mediated by LOV1 with virus-induced gene silencing. We determined SUPPRESSOR OF THE G2 ALLELE OF SKP1 (SGT1), a gene required for the function of many resistance genes, is required for victorin sensitivity and involved in LOV1 protein accumulation. We screened a normalized library and identified six genes that suppressed victorin-mediated cell death and cell death induced by expression of the RESISTANCE TO PERONOSPORA PARASITICA PROTEIN 8 (RPP8) resistance gene: a mitochondrial phosphate transporter, glycolate oxidase, glutamine synthetase, glyceraldehyde 3-phosphate dehydrogenase and the P- and T-protein of the glycine decarboxylase complex. Silencing the latter four also inhibited cell death induced by the expression of an autoactive form of the resistance gene PTO, and reduced PTO-mediated resistance to Pseudomonas syringae pv. tabaci. These results provide evidence that victorin-mediated cell death is functionally similar to a resistance response, further supporting the hypothesis that a resistance response is exploited by C. victoriae for pathogenesis in Victoria blight.
Resistance function of LOV1 was evaluated by observing Pseudomonas syringae pv. tomato virulence upon LOV1 activation. The LOV1 response pathway in Arabidopsis was adapted to activate upon infection with Pseudomonas syringae pv. tomato expressing the type III-dependent effector protein AvrRpt2, a well-characterized protease. We developed a construct to express a beta-glucuronidase (GUS) and TRX-h5 fusion protein separated by an AvrRpt2 proteolytic cleavage site, in which GUS sterically inhibits TRX-h5 function in LOV1-mediated cell death. The fusion is cleaved upon infection by P. syringae pv. tomato expressing avrRpt2, thereby leading to TRX-h5-mediated activation of LOV1 in the presence of victorin. However, when this strain was inoculated with victorin into transgenic LOV1 trx-h5 plants expressing the GUS/TRX-h5 fusion protein, no decrease in pathogen virulence was observed. Technical shortcomings likely prevented observable LOV1 resistance function.
���Graduation date: 2013
Access restricted to the OSU Community at author's request from Oct. 9, 2012 - Oct. 9, 2013
36
Sow, Mounirou El-Hassimi. "Genetic diversity of Oryza species in Niger ; screening and breeding for resistance to rice yellow mottle virus (RYMV)." Thesis, 2012. http://hdl.handle.net/10413/8520.
Full textAbstract:
Rice is a staple food in many West African countries, including Niger. However, both regional and national rice production have failed to meet demand due to several constraints, among which is the Rice yellow mottle virus (RYMV). Moreover, attempted intensification of rice cultivation and the introduction of modern cultivars are encouraging farmers towards abandoning local landraces for high yielding, but often susceptible varieties. The study was primarily oriented towards rice pre-breeding, and identifying priorities for rice breeding in Niger in relation to farmers' preferences and their environment. A secondary aim was the development and evaluation (for release at the regional level) of new breeding lines with resistance to RYMV. This study aimed to: 1) Establish farmers' perception of rice varieties as well as the main constraints on rice production in Niger and particularly those posed by RYMV; 2) Create a collection of rice species from Niger for ex- situ conservation, and to determine the phenotypic variability within this collection; 3) Determine the genetic diversity and population structure of the collection; 4) Screen the collection for resistance to RYMV, so that new sources of resistance could be detected; 5) Improve five elite varieties from West Africa for resistance to RYMV using marker-assisted selection (MAS). The germplasm collection and PRA of this study were conducted in 2008 and 2009 in Niger, while the field and the laboratory researches were conducted in 2008 and 2009 at the Africa Rice Center (AfricaRice) in Benin. For the PRA, data was obtained from a semi-structured group discussion carried out in 14 villages, individual questioning of 153 farmers and visits to farmers' field and storage facilities. The local farmers' union was the only formal seed dissemination system. Seed exchanges between farmers and the use of seeds from previous harvests were important. The RYMV and the bacterial leaf blight (BLB) were cited as the prevalent biotic stresses in the irrigated agrosystem, where the varieties IR1529-680-3 and Waihidjo were found to be the most popular. Flood, birds and hippopotamus were the most damaging agents in the lowland cropping system, and the landrace Degaulle/ D5237 was the preferred variety. Apart from the yield, farmers preferred varieties with good grain quality (milling quality and good taste), high market value, stress tolerance (drought, flood, disease, birds, rodents), and those recommended by the local farmers' association. These findings should be included in breeding goals, seed production and dissemination systems. During collection, a total of 270 rice accessions were assembled, comprising the two cultivated rice species Oryza sativa L. and O. glaberrima Steud. and its two wild relatives Oryza barthii A. Chev. and O. longistaminata Chev. et Roehr. The region of the Niger River and its tributary (the Dallol Maouri) provided the majority (80.7%) of the accessions. Apart from a few wild O. barthii accessions, the accessions found around Lake Chad and the Komadougou river (South-East) were also collected in the Niger River area. Farmers' naming and ecological classification of rice varieties was generally consistent. Three major phenotypic groups were found during the field trials, and the overall phenotypic variability of the collection (as measured by the Shannon-Weaver Diversity Index) was relatively high. There was no significant difference in diversity between the main eco-geographical zones of collection, as well as between the identified phenotypic groups, suggesting a high level of germplasm exchange between the regions in Niger.
From the collection, 264 accessions were genotyped from the collection using 18 well distributed SSR markers and two main genetic compartments were detected, comprising O. sativa subsp. indica varieties and O. glaberrima and its wild relative O. barthii and O. longistaminata. The O. sativa group in Niger was divided into irrigated and floating rice, bound by lowland rice. The wild progenitor O. barthii was widespread but without any clear genetic differentiation from O. glaberrima, probably due to the presence of admixtures within the collected samples of O. barthii. Allelic diversity was relatively high, despite the geographical distance from the centre of domestication of African rice, and the points of entry of Asian rice to Africa. The findings reflect the underuse of Niger's rice landraces genetic potential for rice breeding, given that all the "improved" varieties released during the last 25 years in Niger were clustered together on the dendrogram. The response of a set of the rice collected from Niger and some accessions from Mali to inoculation by RYMV was evaluated using five different virus isolates from Niger (3), Benin (1) and Burkina Faso (1). All rice varieties were susceptible to the disease. However, depending on the virus strain, a few O. glaberrima accessions displayed partial resistance, similar to the highly resistant TOG5681. Allelic research based on primers derived from the RYMV1 gene revealed one accession with allele rymv1-3, and two accessions with allele rymv1-4, and one accession with a different resistance gene. The implications of the finding were discussed and a strategy proposed for breeding varieties with a comprehensive resistance to RYMV.
After three generations of backcrossing, the major resistance gene of the variety Gigante was successfully introgressed into five elite rice varieties of West Africa by Marker-Assisted Backcross (MABC). The newly developed BC3F3 progenies were screened for resistance to RYMV in farmers' fields in Guinea and Mali and also under controlled conditions in a screenhouse in Benin. As shown by low virus content and level of disease incidence, low tiller number and plant height reduction, the transferred gene was fully functional in the new genetic background. Moreover, some lines also displayed a high level of resistance to rice blast (Pyricularia oryzae) and stem borer infestation in Guinea. Four of those lines are in the second year of multi-location trial in seven West African countries. Therefore, effective deployment of the newly developed varieties, coupled with good cultural practices, should reduce the damaging effects of RYMV in lowland and irrigated rice cropping systems and thereby increase the income of small scale farmers from rice cultivation.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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Mafu, Nothando Fowiza. "Marker-assisted selection for maize streak virus resistance and concomitant conventional selection for Downy Mildew resistance in a maize population." Thesis, 2013. http://hdl.handle.net/10413/10023.
Full textAbstract:
Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila, Naude), and maize downy mildew (DM) disease caused by Peronosclerospora sorghi (Weston and Uppal) Shaw, are major contributing factors to low maize yields in Africa. These two diseases threaten maize production in Mozambique, thus the importance of breeding Mozambican maize varieties that carry resistance to these diseases. Marker-assisted selection (MAS) was employed to pyramid MSV and DM disease resistant genes into a single genetic background through simultaneous selection. Firstly, it was essential to determine the genetic diversity of MSV disease resistance in 25 elite maize inbred lines to aid in the selection of suitable lines for the introgression of the msv1 gene; and subsequently, to introduce the msv1 resistance gene cluster from two inbred lines, CM505 and CML509, which were identified as the ideal parental lines for the introgression of MSV disease resistance into a locally adapted Mozambican inbred line LP23 that had DM background resistance. Pyramiding the resistance genes by the use of simple sequence repeat (SSR) molecular markers to track the MSV gene cluster was investigated in 118 F3 progeny derived from crosses of CML505 x LP23 and CML509 x LP23. High resolution melt (HRM) analysis using the markers umc2228 and bnlg1811 detected 29 MSV resistant lines. At the International Maize and Wheat Improvement Centre (CIMMYT) in Zimbabwe, MSV disease expression of the 118 F3 progeny lines was assessed under artificial inoculation conditions with viruliferous leafhoppers and the effect of the MSV disease on plant height was measured. Thirty-seven family lines exhibited MSV and DM (DM incidence ≤50) disease resistance. Individual plants from a total of 41 progeny lines, that exhibited MSV disease severity ratings of 2.5 or less in both locations within each of the F3 family lines, were selected based on the presence of the msv1 gene based on SSR data, or field DM disease resistance, and were then advanced to the F4 generation to be fixed for use to improve maize hybrids in Mozambique for MSV resistance. Simultaneous trials were run at Chokwe Research Station in Mozambique for MSV and DM disease assessment, under natural and artificial disease infestation, respectively. Thus the MSV and DM genes were effectively pyramided. Lines with both MSV and DM resistance were advanced to the F4 generation and will be fixed for use to improve maize hybrids in Mozambique for MSV and DM resistance, which will have positive implications on food security in Mozambique. This research discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. It was concluded that a conventional maize breeder can successfully use molecular markers to improve selection intensity and maximise genetic gain.Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Fato, Pedro. "Investigation of heterotic patterns and genetic analysis of Downy mildew resistance in Mozambican lowland maize (Zea mays L.) germplasm." Thesis, 2010. http://hdl.handle.net/10413/5037.
Full textAbstract:
In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%,
respectively, of area under maize production, but grain yield is compromised by downy
mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal)
Shaw), and lack of appropriate varieties, especially hybrids. Among other factors,
productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding
than open pollinated varieties. Development of a viable hybrid-breeding programme
requires knowledge of genetic effects governing yield and DM resistance in inbreds, and
effective germplasm management requires heterotic groups and heterotic patterns to be
established. In addition, knowledge of farmer-preferred traits is required. Currently, such
information is not available to the hybrid-breeding programme in Mozambique. The
objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and
major production constraints, ii) to determine combining ability effects of inbred maize S4
lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic
patterns among the elite inbred maize lines, and iv) to investigate gene effects governing
resistance to DM in breeding source inbred maize lines from the breeding programme in
Mozambique.
During 2007/08, 142 households were involved in a survey conducted in three
districts representing two maize agro-ecological zones in Mozambique. Formal surveys and
informal farmer-participatory methods were employed and data subjected to analysis in the
SPSS computer programme. Results indicated that there was a low utilization of improved
varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of
the major production constraints and could discriminate constraints according to their
importance for their respective communities. For the lowland environment, farmers
identified downy mildew, drought, and cutworm and stem borer damage as the main
constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and
fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among
the major constraints limiting productivity. The most important variety selection criteria were
grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil
fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the
breeding programmes for the lowland and mid altitude environments in Mozambique.
To determine combining ability for downy mildew resistance, heterotic groups and
heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were
crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at
two sites under DM. Preponderance of GCA effects indicated that additive gene effects were
more important than non-additive gene effects in governing both grain yield and downy
mildew resistance in the new maize lines. Based on specific combining ability (SCA) data,
lines for yield were classified into two heterotic groups, S and Z; whereas based on
heterosis data, lines were fitted into three heterotic groups (S, Z and SZ).
Further heterotic patterns and gene action for yield were determined by subjecting
nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The
diallel crosses, three hybrid checks and the two testers were evaluated in six environments
in Mozambique. Results revealed that non-additive gene effects were predominant for yield
components. In addition, high levels of heterosis for yield was observed and three heterotic
groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred
elite maize lines were observed. Topcrosses with yield levels comparable to single cross
hybrids were also identified, and these would be advanced in the testing programme with
potential for deployment as alternative cheaper and sustainable technology to conventional
hybrids for the poor farming communities in Mozambique.
To determine gene effects for downy mildew resistance in potential breeding lines,
two maize populations were derived from crosses between downy mildew susceptible line
LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies
(BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both
inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of
the populations were evaluated at two sites under downy mildew infection. A generation
mean analysis was performed in SAS. It was revealed that downy mildew resistance was
influenced by genes with additive and dominance effects, plus different types of epistatic
effects such as additive x additive, and dominance x dominance. Overall results indicated
that genes with predominantly non-additive effects controlled resistance in DRAC, whereas
resistance in Suwan-L1 was largely influenced by additive gene effects. These findings
have serious implications on the effective use of these downy mildew resistance sources in
breeding programmes that aim to generate varieties with downy mildew resistance.
Overall, results suggested that inbreeding and selection within heterotic groups,
followed by hybridization between inbreds within and across heterotic groups would be
effective to generate new hybrids. The breeding programme will consider development of
conventional hybrids, such as single crosses and three way crosses, and top crosses.
Implications of the findings of the study and recommendations are discussed.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
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Mwimali, Murenga Geoffrey. "Genetic analysis and response to selection for resistance to two stem borers, Busseola fusca and Chilo partellus, in tropical maize germplasm." Thesis, 2014. http://hdl.handle.net/10413/10943.
Full textAbstract:
Maize is the principal staple food in sub-Saharan Africa (SSA), but production lags behind population growth. The African stem borer, Busseola fusca, Fuller (Lepidoptera, Noctuidae), and the spotted stem borer, Chilo partellus, Swinhoe (Lepidoptera, Crambidae) are serious insect pests of maize in tropical environments. The damage can be managed by breeding stem borer resistant maize varieties but there is limited information that can be used to devise appropriate breeding programs. Therefore breeding investigations were conducted to appraise germplasm screening methods, and to determine combining ability, heterosis and response of maize populations to S1 progeny recurrent selection. The study was conducted in Kenya during 2010 to 2013.
The results showed that most of the test genotypes were susceptible to B. fusca and less so to C. partellus, indicating that breeding for B. fusca would be more challenging. Therefore more resources would be required to improve maize germplasm for resistance to B. fusca to broaden the base from which breeders will select suitable lines for breeding. There was a highly significant (r=0.947, p≤ 0.01) correlation between rank selection index in the greenhouse and laboratory. The detached leaf disk bioassay method was effective for screening maize genotypes for resistance to both stem borers. Therefore it will be recommended for use in screening maize genotypes in future studies. The line x tester studies indicated a preponderance of the additive gene effects for borer resistance traits. Specific combining ability effects were significant for resistance traits and grain yield indicating that non-additive effects were also influential. Findings from the breeding investigations will impact positively on both food security and plant breeding capacity. The completed study was successful in identifying new maize inbred lines with resistance to both stem borers. These lines have high utility to maize breeding programmes that emphasise stem borer resistance in tropical environments. For the hybrid-oriented programmes, combining ability and heterotic orientation data for the 66 maize inbred lines will be crucial. In this regard the study was very successful in classifying the lines into three heterotic groups according to single cross testers (CML395/CML444, and CML312/CML442) that are widely used at CIMMYT, and by public breeding programs throughout SSA. Importantly, this was done based on grain yield potential of hybrids under B. fusca and C. partellus infestations in three mega environments.
The study demonstrates that S1 progeny recurrent selection is effective for improving stem borer resistance, without compromising yield. There was significant reduction (69%) in maize plant damage by both pests, and yield gains of 25% to 70% were realised in two populations. This represents significant contribution to plant breeding capacity, especially to maize breeding programmes that emphasise stem borer resistance in hybrids.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2014.
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Mhora, Terence Tariro. "Genomics of quantitative resistance to brown rust (Puccinia melanocephala) in a sugarcane breeding population." Thesis, 2012. http://hdl.handle.net/10413/10036.
Full textAbstract:
The Sugarcane Industry contributes approximately 400 000 jobs and ZAR 8 billion annually to South Africa’s economy. Due to climate change and the subsequent threat posed by disease, these figures have been on the decline. Brown rust, a contributor to this decline is caused by the basidiomycete Puccinia melanocephala Syd. and P. Syd., which previously resulted in 50% yield losses in susceptible varieties. This highlighted the need for improved screening and breeding techniques which will result in the replacement of susceptible varieties.
The objectives of this study were to:
a) Adopt and optimise a glasshouse whorl inoculation screening technique applicable for mass screening of large populations.
b) Develop a rapid and cost effective rust resistance screening technique using detached leaves.
c)Utilise two flanking marker sets (R12H16 and 9O20-F4-PCR primers) for the rust resistance Bru1 gene in a diagnostic polymerase chain reaction (PCR) to identify rust resistant genotypes lacking Bru1 and possessing either quantitative resistance or an alternative major qualitative resistance gene.
d) Correlate rust phenotypic data to AFLP marker data for the Linkage Disequilibrium (LD2) mapping population.
e) Utilise suppression subtractive hybridization (SSH) profiling on rust challenged genotypes to discover differentially expressed genes between susceptible and resistant (susceptible Bru1 negatives taken away from resistant Bru1 negatives); and resistant genotypes (resistant Bru1 positives taken away from resistant Bru1 negatives). 4
Results from the glasshouse whorl inoculation trials showed the technique could be reliably used to screen large populations, as two independently conducted pot trials showed highly correlated rust ratings. A visually assessed detached leaf assay (DLA) was developed using selected genotypes. Chlorophyll fluorescence and SPAD readings were used in the DLA to determine the leaf photochemical efficiency (PIABS) with relation to chlorophyll content, resulting in reduced assessment time of at least two days. PCR diagnostics revealed 31% of LD2 did not possess either flanking marker, 8% had one or the other marker, and 61% had both markers. The overall rust phenotypic ratings (rating scale of 0-10) and Bru1 status of the genotypes was used to group the population, with the Bru1 negative genotypes containing all three rating categories (resistant 0-3.5; intermediate 3.51-6.5; susceptible 6.51-10); while the Bru1 positive genotypes were all resistant. The phenotypic data was correlated to AFLP data using the Pearson product-moment correlation coefficient and stepwise multiple linear regression employed to build marker based models to use for predicting non-Bru1 mediated resistance. SSH analysis was then subsequently conducted on genotypes selected on the basis of Bru1 status and AFLP correlation data. Two subtraction cDNA libraries were constructed and the cDNA inserted into electro-competent Escherichia coli cells. PCR on transformed cells revealed cDNA inserts ranging from 200- 1300bp. BLAST analysis of the cDNA sequences indicated the presence of high proportions of disease and drought stress related sequences in the libraries. Analysis of the sequences in both libraries showed that the resistant Bru1 negative genotypes contained oxidative stress related sequences which were however absent in the Bru1 positive resistant genotypes. The library comparing the Bru1 negative resistant genotypes against the Bru1 negative intermediate and susceptible genotypes showed a higher proportion of differentially expressed sequences coding for putative disease resistance proteins, highlighting their presence in the resistant genotypes. Both subtraction libraries also contained high proportions of a leucine rich repeat protein coding cDNA which contained a conserved domain homologous to that of a disease resistance protein conferring resistance to Pseudomonas syringae in Arabidopsis thaliana. The outcomes of this study will subsequently enable an improved understanding of sugarcane-rust resistance mechanisms and improved breeding and screening techniques for sugarcane by identifying SSH and AFLP markers linked to rust resistance QTLs or alternative R genes.Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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Yao, Nasser Kouadio. "A genetic study of resistance to African Rice Gall Midge in West African rice cultivars." Thesis, 2012. http://hdl.handle.net/10413/7989.
Full textAbstract:
The African Rice Gall Midge (AfRGM), Orseolia oryzivora Harris and Gagné (Diptera: Cecidomyiidae), is an endemic rice pest found throughout Africa. The failure of most other control methods imposes the need to use crop resistance. This study was initiated: (1) to develop an accurate method for assessing damage caused by AfRGM; (2) to determine AfRGM resistance genes’ modes of action, the heritability estimates of their resistance to AfRGM and the behavioural pattern of progenies with resistance to AfRGM attack; (3) to reveal convergent evolution of same or similar resistance gene(s) in geographically distinct landraces, or divergent evolution of genotypes carrying the same gene, by analysing the genetic diversity among five AfRGM parental lines; (4) to build a core sample of progenies to be used as a reduced mapping population, largely reflecting the entire genome of the whole population, after an estimate of the heritability of 15 agro-morphological descriptors and; (5) determine Simple Sequence Repeat (SSR) markers flanking genes or quantitative trait loci (QTLs) linked to resistance to AfRGM.
A method of accurately assessing damage caused by AfRGM was determined by comparing four methods of assessment including the International Rice Research Institute’s (IRRI) Standard Evaluation System (SES) for rice and three methods based on resistance index (RI) assessments differing in the computing of the percentage of tillers with galls on a resistant check variety. The RI-based assessment (RI-BA) methods consistently provided a better evaluation of AfRGM damage than the SES, regardless of the trial size. Within RI-BA methods, RI-BA2 was always more accurate than RI-BA1 and RI-BA3 when the plot was large. RI-BA2 and RI-BA3 were equally accurate when the plot size was small, and they provided better estimates than RI-BA1. When the plot was of medium size, RI-BA2 was more accurate than RI-BA3; RI-BA3 also surpassed RI-BA1. Overall, the best method of assessing AfRGM damage was RI-BA2, regardless of the plot size.
Five rice populations including F1, F2 and F3 generations involving ITA306, a susceptible variety of Oryza sativa subsp. indica, and four varieties having different reactions against AfRGM were used to determine the genetic basis of resistance and estimate the heritability of resistance to AfRGM. All the F1s were susceptible, suggesting recessive gene inheritance. The F2 generations’ segregation pattern of 1R:15S in both ITA306-TOS14519 and
ITA306-TOG7106 crosses as well as the segregation of 1R:8Seg:7S in ITA306-TOS7106 F3 families indicated that the AfRGM resistance expression being studied is governed by two genes. The deviation of the segregation patterns of crosses involving ITA306 and the tolerant parental lines from Mendelian segregation ratios suggests that the tolerance to AfRGM shown by BW348-1 and Cisadane is under complex mechanisms of control rather than under simple genetic control. The narrow-sense heritability estimates of resistance to AfRGM were low in populations involving tolerant varieties and were high in populations involving resistant varieties. They ranged from 0.086 in the ITA306-Cisadane population, to 0.4 in the ITA306-TOG7106 population. Conversely, the broad-sense heritability estimates ranged from 0.23 (ITA306-Cisadane) to 0.63 (ITA306-TOS14519).
The behavioural patterns of progenies against AfRGM attack were evaluated for 532, 413 and 479 F2 progenies from ITA306-BW348-1, ITA306-Cisadane and ITA306-TOS14519 crosses, respectively, in addition to 90 BC1F2 progenies from the ITA306 and TOG7106 cross. One F3 generation of 649 families from a cross between ITA306 and TOS14519 was also tested. Four types of behavioural pattern categories were observed: (1) progenies were more resistant than the resistant check entry at 45 DAT and 70 DAT; (2) progenies were more resistant at 45 DAT and became susceptible at 70 DAT; (3) progenies were susceptible at both 45 DAT and 70 DAT; (4) progenies were susceptible at 45 DAT but reverted to resistant at 70 DAT. The first three categories were the most frequently observed and occurred in all cross combinations. The last category was observed only for a few progenies from the ITA306-TOS14519 F2 and F3 generations and, surprisingly, many from the ITA306 and BW348-1 cross.
Heritability estimates were calculated for 15 major traits in an F3 population in order to predict the genetic gain associated with each trait, together with the resistance to AfRGM and to estimate the influence of the environment on phenotypic values. Broad-sense heritability (H2) estimates were high for the penultimate leaf length (PLL) - 0.99, penultimate leaf width (PLW) – 1.0, flag leaf length (FLL) - 0.99, flag leaf width (FLW) – 1.0, ligule length (LigL) - 0.99, tillering ability (Til) - 0.99, number of days to booting (DB) - 0.95, number of days to first heading (DFH) - 0.96, number of days to heading (DH) - 0.89, number of days to maturity (DM) - 0.98, culm length (CL) - 0.99, plant height (PH) - 0.99, panicle length (PanL) - 0.95, secondary branching (SB) - 0.95 and the thousand grains weight (TGW) - 0.71. Conversely,
narrow-sense heritability estimates were very low (nearly 0) in PLL, FLL, Lig, DB, DFH, DM and SB or low (at most 0.267) in PLW, FLW, DH and PH, with a high value of 0.727 for TGW. Inheritance of the traits studied was therefore under non-additive gene effects rather than additive genetic effects and can therefore be improved using pedigree breeding schemes along with breeding for AfRGM resistance.
Fine genetic evaluation of five AfRGM parental lines was studied in terms of polymorphisms using 303 SSR primers covering the rice genome. Of the 178 polymorphic primers identified, 60 were highly polymorphic and informative. The number of alleles amplified by these primers ranged from one to five for a total of 1,041 alleles. The polymorphism rate was globally high, ranging from 45.2% to 66.8%. The mean of the polymorphism information content (PIC) was 0.553. Factorial analysis, based on the allelic diversity, demarcated the parental lines into Oryza glaberrima Steud, Oryza sativa subsp. japonica and O. sativa subsp. indica groups, while a cluster analysis distinguished them into four groups: AfRGM resistant, susceptible, moderately resistant and tolerant. BW348-1 and Cisadane showed the least diversity, despite their distant geographical origins. TOS14519 and TOG7106 showed more divergence to ITA306 despite their common West African origin. This variability amongst the genotypes tested is the result of farmer-based selection for AfRGM resistance rather than direct breeding efforts through breeder intervention.
A method of selecting individuals for a mapping population, based on a core sample, was developed in order to speed up the mapping procedure. A diversity study amongst F2 and F3 generations involving 15 quantitative and 26 qualitative agro-morphological characters was carried out and led to the dropping of seven non-discriminant descriptors. The diversity index (H) was calculated for each remaining character and the discriminant descriptors were selected based on a diversity index threshold value above 0.4. Four descriptors of H values less than 0.35 were therefore dropped. The sizing of the core collection of 64 individuals and the selection of these individuals were done using MSTRAT version 4.1 package in redundancy mode, a construction run of 100 times with an iteration number of 500. The core sample was similar to the whole population for clustering pattern, minimum and maximum quantitative values and diversity index, while mean values and coefficient of variation distinguished them. The core sample, which represents 10% of the whole population, also revealed the same phenotypic variation and the same genotypic segregation according to two SSR markers. It can therefore efficiently reflect the whole population as a mapping population.
Finally, a study was undertaken to identify flanking markers to the gene/QTL involved in the resistance against AfRGM using bulked segregant analysis (BSA). A polymorphism study between ITA306 and TOS14519 displayed 145 polymorphic SSR markers, which were used to screen the bulks that originated from the two tails, and depicted only two SSRs as candidate markers linked to gall midge resistance. These markers included RM317 and RM17303 which displayed strong significance after an analysis of variance using an F test, meaning that they were segregating with the resistant alleles.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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Moodley, Vaneson. "Development of a pepper (Capsicum annuum L.) hybrid variety with resistance to potato virus Y (PVY) using molecular breeding." Thesis, 2013. http://hdl.handle.net/10413/10829.
Full textAbstract:
Pepper (Capsicum annuum L.) is an important vegetable crop grown and consumed worldwide. Potato virus Y (PVY) is a globally economically important pathogen which significantly reduces the yield and quality of cultivated pepper. The virus is considered as a major limiting factor to the economic production of pepper in the province of KwaZulu-Natal (KZN) in the Republic of South Africa (RSA). Many applied practices to control the spread of PVY are ineffective to mitigate the losses incurred by many farming communities across the KZN province. Therefore, the objectives of this study was to determine the full genome sequence of a PVY isolate from KZN, to identify resistance alleles in commercially available pepper varieties in KZN and to develop a pepper hybrid variety with resistance to PVY using a molecular breeding strategy
The first part of the study was conducted to determine the first full genome sequence of a PVY isolate (JVW-186) infecting pepper from KZN. The complete genome sequence of JVW-186 was assembled from overlapping RT-PCR clones using MEGA 5 software. Individual ORFs were identified using the nucleotide data base NCBI and aligned using CLUSTALW. RDP4 software was used to identify recombination junctions in the sequence alignment of JVW-186. CLC Main Workbench 6 software was used to determine the nucleotide sequence similarity of recombinant and non-recombinant fragments of JVW-186 in conjunction with ten PVY parental isolates. Based on sequence data, virus morphology and the coat protein size as determined by SDS-PAGE analysis, the identity of the isolate JVW-186 was confirmed as PVY. Phylogenetic trees were constructed from all recombinant and non-recombinant segments of the sequence by the maximum likelihood method using MEGA 5 software. The full length sequence of JVW-186 consisted of 9700bp. Two ORF’s were identified at position 186 and 2915 of the sequence alignment encoding the viral polyprotein and the frameshift translated protein P3N-PIPO, respectively. RDP4 software confirmed two recombination breakpoints at position 343 and 9308 of the sequence resulting in four segments of the genome. At each recombination event, a 1021-bp fragment at the 5’
end in the region of the P1/HC-Pro protein and a 392-bp fragment in the region of the coat protein shared a high sequence similarity of 91.8 % and 98.89 % to the potato borne PVYC parental isolate PRI-509 and the PVYO parental isolate SASA-110 respectively. The non-recombinant fragment 1 clustered within the C clade of PVY isolates; however the large 7942-bp fragment 3 did not cluster within any of the clades although it shared > 80% nucleotide sequence similarity to other PVY isolates used in this study. Our results suggest that isolate JVW-186 is a novel recombinant strain of PVY that could have evolved due to the dynamics of selection.
The second part of the study aimed to evaluate different pepper lines for resistance to PVY. Two recessive alleles (pvr21 and pvr22) located on the pvr2-elF4E locus are known to confer resistance to the virus. To this end, six pepper lines were challenged with PVY infected Nicotiana tabacum cv. Xanthi leaf material using mechanical inoculation under greenhouse conditions. Each line was assessed for resistance to PVY by visual screening for disease severity and quantitative enzyme linked immunosorbent assay (ELISA) for virus load. Pepper lines were further characterized using tetra-primer ARMS-PCR (amplification refractory mutation system polymerase chain reaction) to identify and differentiate the presence of homozygous/heterozygous resistance alleles that confer PVY resistance. Evaluations revealed two resistant pepper lines (Double Up and Cecelia) and varying levels of susceptibility in the other four pepper lines challenged with PVY. The most susceptible pepper line was Benno, although high levels of susceptibility were observed in three other lines (IP, Mantenga and Excellence). The pvr2+ allele was positively identified in all the susceptible pepper lines using the T200A tetra-primer which confirms that the presence of this allele is dominant for PVY susceptibility. Double Up and Cecelia were genotyped homozygous pvr21/pvr21 and pvr22/pvr22 respectively, and remained asymptomatic throughout the trial which indicates that these alleles confer resistance to the isolate of PVY used in this study. The information generated in this study can be incorporated into breeding programs intended to control PVY on pepper in KZN.
The final part of the study focused on the development of resistant varieties as the best alternative to manage PVY diseases on pepper. Homozygous F2 pepper lines were
developed from local germplasm carrying PVY resistance genes (pvr21 and pvr22) using marker assisted selection (MAS). The F1 progeny was obtained by crossing a homozygous pvr21 (resistant) ‘Double Up’ cultivar with a heterozygous susceptible (pvr2+/pvr22) ‘Benno’ cultivar. F1 and F2 generations were assessed for the presence of PVY resistance/susceptibility alleles (pvr2+/pvr21/pvr22) at the pvr2-elF4e locus using the tetra primer amplification refractory mutation system – polymerase chain reaction (ARMS-PCR) procedure. Negative selection was carried out using the tetra-primer T200A marker to detect the pvr2+ (susceptible) allele. All F1 progeny displaying the pvr2+ allele were eliminated from further study. All 302 plants belonging to 29 F2 families expressing homozygous recessive traits were tested via mechanical inoculation for their response to PVY infection and resistance to PVY was confirmed in all selected families based on symptomatology in greenhouse house screens using double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA). These results show that ARMS-PCR can be used to successfully screen pepper genotypes for alleles that confer PVY resistance thereby contributing to the improvement of pepper production using molecular breeding approaches.Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Mweshi, Mukanga. "Genetic improvement of Zambian maize (Zea mays L.) populations for resistance to ear rots and a survey of associated mycotoxins." Thesis, 2009. http://hdl.handle.net/10413/519.
Full textAbstract:
Maize ear rots are among the most important impediments to increased maize production in Africa. Besides yield loss, they produce mycotoxins in their host whose contamination has been linked to several human and animal mycoses. The main objectives of the studies reported on in this thesis were (i) to investigate farmer perceptions of maize ear rot disease and prospects for breeding for host plant resistance in Zambia; and (ii) to establish the levels of incidence and extent of maize ear rot infection as well as the level of mycotoxins in the maize crops of smallholder farms in central and southern Zambia; (iii) to appraise the field inoculation techniques and assess them for their suitability for the Zambian environmental conditions, (iv) to determine the combining ability of Zambian maize populations for resistance to ear rot and investigate the genetic basis of this resistance; and (v) to investigate both direct and indirect responses to full-sib selection for ear rot resistance in Zambian maize populations. A participatory rural appraisal (PRA) was conducted in four communities, involving a total of 90 farmers. Participatory methods were used, such as focused group discussions, group interviews, participant scoring and ranking. Farmers ranked and scored the various constraints affecting their maize production in general and the maize ear rots in particular. Ear rots were ranked as the third most important biotic stress and it was evident that although farmers were aware of the disease, they were not aware of mycotoxins. This was reflected in the way they disposed of rotten maize: either by feeding livestock or eating it in periods of hunger. The survey of ear rots and mycotoxins was carried out in the Southern and Central Provinces of Zambia. A total of 114 farms were covered in the survey: maize samples were collected and both ear rot fungi and mycotoxins were isolated. Fusarium and Stenocarpella were the most frequently isolated fungi from smallholder farms. The levels of fumonisins on these farms ranged from 0.05 to 192 ppm, while those of aflatoxins were between 1.5 and 10.6 ppb. In 50% of the farmsteads surveyed, the mycotoxins, i.e. fumonisins and aflatoxins, exceeded the recommended FAO/WHO 1limits of 2 ppm and 2 ppb, respectively. Five field inoculation techniques namely, colonised toothpick, leaf whorl placement, ear top placement, spore suspension spray, and silk channel injection, were evaluated over three seasons in a series of experiments. It was found that the leaf whorl placement of inoculums, followed by colonized toothpick method, gave a constant ranking of genotypes across locations and years compared to the other three methods. In addition, the use of a mixture of ear rots as inoculum was as effective as its principal single species constituents. In the population diallel analysis, five broad-based maize populations were crossed in a diallel and evaluated under artificial ear rot inoculation using an inoculum mixture of three ear rot fungi, Aspergillus flavus, Fusarium verticilloides and Stenocarpella maydis at four locations in Zambia. The purpose was to estimate general (GCA) and specific combining ability (SCA) and investigate genotype x environment interaction. GCA effects were found not to be significant for disease severity but were significant for grain yield across environments. Populations with a strong GCA effect for disease severity across sites included PRA783244c3, Pop25, MMV600, and ZUCASRc2. Across sites, the F1 combinations, MMV600 x Pop25, ZUCASRc2 X Pop25, and Pop25 x PRA783244c2 had strong SCA effects for root lodging, ear drooping, husk cover and ear insect damage. In a related diallel analysis of 10 full-sib families derived from these populations, it was observed that resistant x susceptible families and their reciprocal crosses performed better than their resistant parents, suggesting an over dominant expression of resistance. Both maternal and non maternal effects were observed to be influencing resistance to ear rots. There was a preponderance influence of non-additive gene action. A response to full-sib recurrent selection was conducted in four locations in Central Zambia. Out of the 343 families created in 2005/6 season, 10% were selected from each population and recombined to create five new populations. These, with the original populations, were evaluated in four sites during the 2007/8 season. There was a net reduction in ear rot incidence and rot severity in the new synthetic population. Pop10 had the largest reduction in disease severity. The predicted gain per cycle was -4.1% and realized gain was -2.5% for disease incidence, and 0.19% and 19.4% for grain yield. Genetic variability was maintained though with low heritability estimates. Negative but at times strong association between grain yield and ear rot disease severity was detected suggesting that in general selecting for ear rot resistance would enhance grain yield in the five populations. Overall the importance of the ear rots and mycotoxins in compromising yield and health of the communities in Zambia, respectively, were confirmed and support the call to improve maize varieties for resistance to ear rots. The results indicate that the five populations could be enhanced for ear rot resistance through population improvement procedures such reciprocal recurrent selection that exploit both additive and non-additive variation. Selection might be compromised by the large genotype x environment interaction effects, and large reciprocal effects and their interaction with the environments. To enhance repeatability genotypes should be artificially inoculated, by placing the inoculum in the leaf whorl followed by colonized toothpick inoculation, and screened in many environments to identify genotypes with stable resistance to ear rots.Thesis (Ph.D) - University of KwaZulu-Natal, Pietermaritzburg, 2009.
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Bucheyeki, Tulole Lugendo. "Characterization and genetic analysis of maize germplasm for resistance to northern corn leaf blight disease in Tanzania." Thesis, 2012. http://hdl.handle.net/10413/8730.
Full textAbstract:
The majority of farmers in Tanzania have not yet adopted modern maize varieties and still
cultivate landraces and open pollinated varieties (OPVs) with low production potential and
susceptible to diseases like maize streak virus (MSV), grey leaf spot (GLS) and northern corn
leaf blight (NLB). The NLB disease is among the major causes of low yield and has been
reported in all 21 maize growing regions in Tanzania. Breeding for host plant resistance with
high yielding potential and involving the community in the breeding process is expected to
address the problem of low yield, NLB disease susceptibility and low rate of F1 hybrid adoption.
Therefore, the study was conducted to obtain additional sources of resistance to NLB disease,
high yielding cultivars with community acceptable traits adapted to Tanzanian conditions. The
main objective was to contribute to increased maize productivity in the western zone of
Tanzania. The specific objectives of this study were therefore to : 1) investigate maize
production limiting factors for smallholder farmers in western Tanzania, 2) identify farmers and
stockist perceptions, opinions and maize variety selection criteria in western Tanzania, 3)
establish NLB disease status in farmers’ fields of western Tanzania, 4) determine the genetic
relationships among landraces and assess maize landraces as sources of breeding materials,
5) determine the combining ability and heterosis for NLB disease resistance of eleven maize
inbred lines adapted to Tanzanian conditions, and 6) determine the gene action and inheritance
of resistance to NLB disease in five maize inbred lines adapted to Tanzanian conditions. The
study was conducted from 2008-2011 in three diverse environments which represent all the
maize growing regions in the country
The participatory rural appraisal (PRA) was conducted in three districts to investigate farmers’
and stockists preferred traits for maize selection in western Tanzania, determine maize
production constraints facing farmers and assess NLB disease prevalence in the same area. A
focus group of 30 farmers was selected in each of the three villages. Transect walks, wealth
ranking and historical profiles were used in an informal survey. One hundred and fifty
questionnaires were used in a formal survey. The recorded yield was only 1 t haˉ¹. Thirteen
major maize production constraints, 13 insect pests and vermin and, 11 diseases were
recorded. The NLB disease was reported to be increasing in severity in all farmers’ fields.
Farmers’ preferred traits included resistance to abiotic and biotic stresses, early maturity,
preferred milling qualities, high storage qualities and high yielding potential. Stockists mentioned
12 preferred maize variety traits which included high yielding, disease and insect pest
resistance, heavy grain, large cob size and large grain sizes. Similarity between farmers and
stockist variety preference ranking were found to exist.
The occurrence and distribution of northern leaf blight (NLB) disease study was conducted to
assess the incidence and severity of NLB disease in farmers’ fields in seven districts. The study
was conducted for two seasons. In each season, 175 fields with 5600 plants were sampled.
There were sixteen varieties grown with wide NLB disease reaction variation. Gembe, a
landrace, was among the three observed resistant varieties. The NLB disease has changed its
distribution pattern affecting all districts of the western zone. The disease incidence in season
two (2009/2010) significantly increased from season one (2008/2009) t= -3.25 (348), P= 0.001.
About 30% of both means of blight incidence and severity were recorded in the area.
Characterization and screening of maize landraces for northern leaf blight disease resistance was
conducted to determine the genetic relationships among landraces, assess maize landraces as
sources of NLB disease resistance and assess important agronomic traits for future maize
improvement. Ninety breeding materials consisting of 71 landraces and 19 commercial varieties
were evaluated. The average yield of landraces under research management was 2.3 t haˉ¹.
Landrace TZA 3075 was identified as NLB disease resistant. Yield potential, dent grain texture,
white endosperm and husk cover were important agronomic traits observed among landraces.
There were high variations in terms of morphology and NLB disease resistance among the
landraces. Five principal components contributed to 71.98 % of total variation. Clusters analysis
revealed five distinct groups of landraces. Leaves/plant, infested leaves/plant, lesion number,
lesion length, lesion width and NLB disease incidence traits highly contributed to variation and
grouping of landraces.
Combining ability analysis for northern leaf blight disease resistance was conducted to estimate
the combining ability for NLB disease resistance of 11 maize inbred lines adapted to Tanzanian
conditions, determine maternal effects which are involved in NLB disease resistance in maize
germplasm, and determine the heterosis in the F1 hybrids. A full 11 x 11 diallel cross was
performed. All top ten experimental hybrids in each of the three sites had negative midparent
heterosis for NLB disease severity. The overall mid-parent heterosis means for yield across
sites was 152%. The mean sum of squares for GCA was highly significant (P< 0.001) on
disease severity indicating additive gene action effects. Mean sum of squares for SCA were
highly significant for disease severity and yield implying non-additive gene action effects.
The mean squares for reciprocal effects were highly significant on yield and non-maternal sum
of squares had significant effect (P<0.05) on yield. The GCA contribution was high for disease
severity (91%) and lesion number (85%). Almost, all GCA effects for NLB disease resistance
were negative implying contribution to disease resistance. Due to preponderance of the additive
gene action, recurrent selection could be used to improve the resistance of inbred lines while
the non-additive gene action could be exploited in breeding for disease resistant hybrids.
Generation mean analysis of northern leaf blight disease resistance was conducted to
determine the mode of gene action involved in the inheritance of resistance to NLB disease in
five inbred lines adapted to Tanzania at contrasting environments, estimate heterosis and
heritability in five tropical inbred lines. Generation mean analysis was conducted using a six
parameter model comprising P1, P2, F1, F2, BCP1 and BCP2 generation progenies. The mean
sum of squares for environment, replication with the nested environment, generations,
generations x environment interactions were highly significant (P<0.001). The full model of
additive, dominance, additive x additive and additive x dominance epistatic effects was highly
significant (P<0.001). Nonetheless, the additive gene effects were predominant ranging
between 57% and 89% which was matched by large heritability (54%-85%). The average
degree of dominance ranged between -0.52 and 0.88 supporting observations of partial
dominance. The NLB disease severity showed a continuous distribution in all three sets for F2,
BCP1 and BCP2 populations which is an indication of quantitative nature of inheritance and
additive gene effects. The mid parent heterosis ranged from -19 to 1%. Therefore, resistance to
NLB disease could be improved through selection by exploiting the additive gene effects. The
epistatic gene effects would cause less complications because they were negligible (<25%).
The client oriented breeding for maize northern leaf blight disease resistance was carried out to
perform farmers and stockists assessment on the 110 F1 experimental maize hybrids and
compare them with breeders selection criteria. Breeders selection criteria ranked 10 top high
yielding experimental hybrids. Farmers developed 14 while stockists developed 13 selection
criteria. The most preferred hybrids by farmers were VL 05616 x CML 159, CML 159 x KS03-
0B15-47 and EB04-0A01-304 x CML 442 while stockists preferred VL 05616 x CML 395,
EB04-0A01-304 x CML 442 and VL 05616 x CML 159. Two F1 experimental hybrids EB04-
0A01-304 x CML 442 and CML 159 x CML 442 appeared in all top five ranked hybrids by
breeders, farmers and stockists. Generally, findings showed that, farmers, stockists and
breeders coincide in some selection criteria but also differ in other cases.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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Muitia, Amade. "Farmer perceptions and genetic studies of rosette disease in groundnut (Arachis hypogaea L.) in northern Mozambique." Thesis, 2011. http://hdl.handle.net/10413/9875.
Full textAbstract:
Groundnut (Arachis hypogaea L.) is an important food and cash crop in Mozambique and production has been constrained by lack of high-yielding cultivars and disease infection. Objectives of this study were: 1) to identify farmers’ major groundnut production constraints and their preferences for cultivars; 2) to determine genotypic variation among landraces for agro-morphological traits and resistance to groundnut rosette disease; 3) to determine agronomic performance and resistance to groundnut
rosette disease among advanced groundnut lines; and 4) to determine the inheritance of resistance to groundnut rosette disease. The study was conducted in northern Mozambique from 2008/2009 to 2010/2011. In attempt to identify farmers’ major groundnut production constraints and their preferences in cultivars, a participatory rural appraisal (PRA) was conducted in Namuno and Erati districts in northern Mozambique. Results from the PRA showed that farmers were aware of the constraints affecting groundnut production and productivity in the study area. The major constraints included groundnut rosette disease, insect pests, lack of seeds and improved cultivars, low soil fertility and lack of infra-structure. Groundnut rosette disease was ranked the most important constraint, and it was widespread in the region. Selection criterion for groundnut cultivars used by women differed from that used by men within village and across villages. However, high yield and oil content were the most important traits preferred by farmers followed by pod and seed size, earliness, disease and insect pest resistance. Fifty-eight groundnut landraces were collected from northern Mozambique (Nampula, Cabo Delgado, Niassa and Zambezia) and evaluated for variation in agro-morphological traits and resistance to groundnut rosette disease. The landraces showed high phenotypic diversity in agro-morphological traits. Clustering by nearest neighbour
method indicated that the genotypes could be grouped into six clusters, indicating that agro-morphological diversity exists. The highest yielding genotypes were Pambara-4, Pambara-2, Pambara-6, lle-1, Imponge-1-Tom and Gile-5. There was considerable genetic variability for resistance to groundnut rosette disease among the landraces. Four landraces (PAN-4, Imponge-4, Pambara-3, Metarica Joao) were classified as resistant. No significant correlation was observed between seed yield and groundnut rosette incidence. Thirty-two improved lines were evaluated for performance in two growing seasons across three locations in northern Mozambique (Nampula, Namapa and Mapupulo). The results indicated that the highest yielding genotype was 23A and the highest yielding location was Namapa. There was a significant and negative correlation between seed yield and groundnut rosette disease indicating that the seed yield was negatively influenced by the disease. The results on stability analysis indicated that genotype 35B was the most stable across environments since it had coefficient of regression around unity (bi=1.024), high coefficient of determination (R2=0.999), and small variance deviation (var-dev=162.8), and 13 % above average seed yield. It is, therefore,
concluded that genotype 35A could be recommended for cultivation on diverse environments of northern Mozambique. A trial was conducted using the parents and F2 populations derived from a 7 X 7 diallel cross. The test materials were infected with groundnut rosette disease using the
spreader-row technique. The results indicated that no genotype was immune to disease. The mean squares due to both general combining ability (GCA) and specific combining ability (SCA) were significant indicating that additive and non-additive gene actions were involved in the expression of resistance to groundnut rosette disease. The general
predictability ratio (GCA:SCA) was 0.97, indicating the predominance of additive over non-additive gene action in the inheritance of the disease. The study also found that groundnut rosette disease was controlled by two recessive genes. However, some genetic modifiers may also be present and influence disease expression. In general, the study revealed that breeding opportunities do exist, incorporating farmers preferred traits and major groundnut production constraints into new groundnut cultivars.
Improving cultivars for resistance to groundnut rosette disease will be a major breeding focus, while selection for other traits and constraints will not be ignored. Resistance has been identified from local landraces. Advanced lines with high yields across environments were identified that can be recommended for release. The high significant additive effects observed for groundnut rosette disease implied genetic advance could
be effective in the F2 and later generations through selection, although modifiers could slow the progress.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Mengesha, Wende Abera. "Genetic diversity, stability, and combining ability of maize genotypes for grain yield and resistance to NCLB in the mid-altitude sub-humid agro ecologies of Ethiopia." Thesis, 2013. http://hdl.handle.net/10413/10935.
Full textAbstract:
Maize (Zea mays L.) is the third most important cereal crops in the world after wheat
and rice. In Ethiopia, maize remains the second largest food security crop after tef
[Eragrostis tef (Zucc.) Trotter.]. The mid-altitude, sub-humid agro-ecology (1000 to 1800
m above sea level) is the most important maize producing environment in Ethiopia.
However, productivity of maize is low, due to several biotic and abiotic constraints.
Among the biotic constraints, Turcicum leaf blight disease of maize caused by
Exserohilum turcicum Pass Leonard & Suggs shows high incidence of 95-100% and
inflicts significant grain losses in the country. Therefore, high yielding, Turcicum leaf
blight resistant and farmers-preferred maize varieties and their production technologies
should be developed and made available to growers to enhance maize production and
to achieve food security.
The objectives of this study were to: (1) assess farmer’s preferences, and production
constraints for maize in the mid-altitude, sub-humid agro-ecology of western Ethiopia,
(2) determine the genetic variability among elite maize inbred lines and select promising
parents for resistance to E. turcicum, (3) determine diversity among the elite germplasm
lines using SSR markers, (4) determine combining ability and heterosis among elite
maize inbred lines and their hybrids, and (5) investigate genotype x environment
interaction and yield stability of experimental maize hybrids developed for the midaltitude
sub-humid agro-ecology of Ethiopia.
A participatory rural appraisal (PRA) research was conducted involving 240 maize
farmers in three representative maize growing zones of western Ethiopia; West Shoa,
East Wollega and West Wollega, each represented by two districts and two subdistricts.
Maize was ranked number one both as food and cash crop by 82.9% of
respondents. Turcicum leaf blight was ranked as number one devastating leaf disease
by 46% of respondents. Breeding for improved disease resistance and grain yield,
enhancing the availability of crop input and stabilizing market price during harvest time
were recommended as the most important strategies to increase maize production by
small-scale farmers in western Ethiopia. Fifty inbred lines were evaluated for reaction to Turcicum leaf blight during the main
cropping seasons of 2011 and 2012. Inbred lines were clustered into resistant
(CML202, 144-7b, 136-a, 139-5j, 30H83-7-1, ILOO’E-1-9, SZYNA-99-F2, and 142-1-e),
and susceptible (CML197, CML464, A7033 , Kuleni C1-101-1-1, CML443, SC22-430
(63), (DRB-F2-60-1-2) – B-1-B-B-B, Pool9A-4-4-1-1-1). Inbred lines (CML312, CML445,
Gibe-1-158-1-1-1-1, CML395, and 124-b (113)) had intermediate response to the
disease. Overall, inbred lines such as CML202, 30H83-7-1, ILOO’E-1-9-1, CML312,
CML395 CML445 and 142-1-e were selected with better agronomic performance and
resistance to leaf blight for breeding. Twenty selected elite parental inbred lines were
genotyped with 20 polymorphic SSR markers. The genotypes used were clustered into
five groups consistent with the known pedigrees. The greatest genetic distance was
identified between the clusters of lines CML-202 and Gibe-1-91.
Eighteen selected inbred lines were crossed using the factorial mating scheme and 81
hybrids developed to determine combining ability effects and heterosis. Inbred lines with
high GCA effect (CML 202, CML395, 124-b (113), ILOO’E-1-9 and CML 197) were
selected as best combiners for hybrid development. Additionally five high yielding novel
single cross hybrids with grain yield of > 8 t ha-1 and high SCA effects were identified
such as CML395 X CML442, DE-78-Z-126-3-2-2-1-1 X CML442, ILOO’E-1-9-1-1-1-1-1
X CML312, X1264DW-1-2-2-2-2 X CML464 and SC22 X Gibe-1-91-1-1-1-1. These
experimental hybrids are recommended for direct production or as hybrid testers for
hybrid development.
Genotype x environment interaction (GEI) effects of 81 newly developed and three
check maize hybrids were evaluated across 10 locations in the mid-altitude sub-humid
agro-ecologies of Ethiopia. The AMMI-3 and GGE biplot models were used to determine
stability. Hybrids such as G68, G39, G37, G77, G34 and G2 were identified as the most
stable and high yielding at favorable environments such as Bako, Jima, Arsi Negelle
and Pawe in Ethiopia. The genotype and genotype by environment interaction (GGE)
biplot clustered the 10 environments into three unique mega-environments. Environment I included Bako, Jima, Asossa, Ambo, Finote Selam, Haramaya and Pawe
while environment II represented by Arsi-Negelle and environment III Areka and
Hawassa.
In general, the study identified valuable maize inbred lines with high combining ability
for breeding and novel single cross hybrids for large-scale production or as testers for
hybrid development at the mid-altitude, sub-humid agro-ecologies of Ethiopia or similar
environments in sub-Saharan Africa.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Tignegre, Jean Baptiste De La Salle. "Genetic study of cowpea (Vigna unguiculata (L.) Walp) resistance to Striga gesnerioides (Willd.) vatke in Burkina Faso." Thesis, 2010. http://hdl.handle.net/10413/5038.
Full textAbstract:
In Burkina Faso, the existence of different races of Striga gesnerioides (Willd.) Vatke, with
apparent variable aggressiveness on cowpea (Vigna unguiculata (L.) Walp) renders the
breeding task very complex. Therefore, a number of studies was carried out from 2006 to
2009 in field, pot and ‘’in-vitro’’ to identify new sources of resistance to three prevailing
Striga races, SR 1, SR 5 and a newly occurring Striga race named SR Kp and to
understand the genetic pattern of the underlying resistance of cowpea germplasm to Striga
races found in Burkina Faso.
To achieve these objectives, the following investigations were initiated: (i) a participatory
rural appraisal (PRA), a participatory variety selection (PVS) and grain quality survey were
implemented to identify cowpea breeding priorities for Burkina Faso Striga hot-spots; (ii) the
identification of sources of resistance in Burkina Faso germplasm, using three prevailing
Striga races of S. gesnerioides as sources of inoculum; (iii) the identification of the
mechanisms of resistance underlying the resistance to Striga in such genotypes; (iv) a
study of combining abilities of selected parents through a diallel cross; (v) a study of the
segregation patterns in crosses involving resistant and susceptible sources and a study of
the allelic relationships between different resistance sources.
The participatory studies conducted in 2007 and 2008 over three districts in Striga hotspots;
there was no effective control method against Striga at farmers’ level. These
investigations highlighted the importance of cowpea across all sites. Rain decline over time,
low input use coupled with a poor extension system were the major constraints mentioned
by farmers. Differential reactions of genotype KVx61-1 for Striga resistance suggested that
different Striga races were prevailing in different areas. Farmers’ preferred traits in cowpea
genotypes were oriented towards grain quality such as big sized grain, white seed colour
and rough texture of cowpea grain, except in Northern-Burkina Faso, where farmers
preferred brown-coloured grain for food. Cowpea was also seen as an income generating
crop.
An evaluation of 108 genotypes was done in 2007 in the field (rainy season) and in pots
(off-season) for Striga resistance assessments. The screening trials enabled the
identification of sources of resistance to S. gesnerioides. Genotypes KVx771-10, IT93K-
693-2, KVx775-33-2, Melakh and IT81D-994 are potential sources of resistance to all three
Striga races with acceptable yield. Landraces were susceptible and late-maturing whilst
most wild species were resistant but with unwanted shattering traits.
A combining ability study for Striga resistance parameters conducted in pots and a
resistance mechanism study conducted ‘’in-vitro’’ were performed using F1 populations from
a 10 x 10 diallel cross. The general combining ability (GCA) effects were significant for the
resistance parameters Striga emergence date (DSE), Striga height above soil (SH), cowpea
grain weight (CGW), hundred grain weight (HGW) for all Striga races involved and Striga
vigour (SVIG) for SR 5 and SR Kp. The pot-screening showed that, regardless of the SR
used as inoculum, the additive genes were important in conferring Striga resistance for
parameters DSE, SH, CGW and HGW. The selection of parents could therefore result in
breeding advance. Complete dominance, partial, over-dominance and non-allelic
interactions (epistasis or failure of some assumptions) were present for some parameters.
The ‘’in-vitro’’ screening showed that additive genes were important, with high narrow sense
heritability values for the resistance mechanisms Striga seed germination frequency (GR)
for SR 1 and SR Kp, the frequency of Striga radicle necrosis before the penetration in
cowpea rootlet (NBP) for SR 5, the frequency of Striga radicle necrosis after the penetration
in cowpea rootlet (NAP) for SR 1 and SR Kp and the susceptibility ‘’in-vitro’’ (SIV) for SR 5
and SR Kp. The selection of parents can be useful in accumulating the genes for Striga
resistance mechanisms in progenies.
The F2 populations derived from crosses between Striga-resistant x susceptible genotypes
were evaluated in Striga infested benches in 2008 and 2009. The segregation patterns
suggest that single dominant genes govern Striga resistance. The test for allelism showed
that two non-allelic genes were responsible for the resistance to S. gesnerioides in cowpea.
A new Striga resistance gene seems to be involved in genotype KVx771-10 resistance to S.
gesnerioides, which confers resistance to all studied Striga races. Gene 994-Rsg in
genotype IT81D-994 which confers Striga resistance to SR 1 and gene Rsg 3 also
conferring Striga resistance to SR 1 segregated differently for the resistance to SR 5
suggesting that they were different but both confer resistance to SR 5.
48
Kam, Honore. "A study of the diversity of Burkina Faso rice landraces and identification of source of resistance to rice yellow mottle virus (RYMV)." Thesis, 2011. http://hdl.handle.net/10413/8518.
Full textAbstract:
The main goals of this study were to ascertain farmers' preferred traits in rice landraces and their perception of Rice yellow mottle virus, to collect rice landraces across Burkina Faso, investigate their genetic diversity, and to exploit this diversity in a search for varieties resistant and tolerant to RYMV, for their utilisation in rice breeding. Farmers' preferred traits, approaches to crop management, and disease perceptions were assessed using a Participatory Research Appraisal (PRA) approach. In the main rice growing regions of Burkina Faso, 330 rice landraces were collected. The agro-morphological diversity of the germplasms was evaluated in the field with 20 quantitative and 30 qualitative agro-morphological parameters. Thereafter, 22 Simple Sequence Repeat molecular markers were used to assess the genetic diversity and the population structure of the collection. Finally, the rice landraces were screened against four RYMV isolates to assess the susceptibility, tolerance and resistance of the landraces in the collection using visual assessment and Enzyme Linked Immunosorbent Assay. The PRA identified sweet taste, grain expansion when cooking, easy cooking and yield as paramount selection criteria in rural rice farming communities in Burkina Faso. Drought and disease resistance are characters that farmers wish to have in their varieties. The PRA also highlighted that farmers are conscious of RYMV disease in their fields. However, they are unaware about the epidemiology of the disease.
An agro-morphological study of the phenotypic diversity of the collection confirmed the presence of the two cultivated rice species: O. glaberrima and O. sativa. There were more O. sativa accessions than O. glaberrima landraces. There were 48 O. glaberrima and 282 O. sativa accessions in the collection. Both species were divided into four clusters, reflecting the richness of the collection. The underlying genetic diversity of the collection was confirmed by the use of 22 Simple Sequence Repeat molecular markers. The neutral markers confirmed the existence of two substructures, namely O. glaberrima and O. sativa, and the presence of admixture varieties. However, a core collection of 52 individuals was developed. This included 13 O. glaberrima and 39 O. sativa accessions. It reflects the genetic diversity of the sub-clusters present in each species. This core collection contains 89% of the allelic richness of the collection. Its small size will facilitate the maintenance and active use of diversity of germplasm in the core collection. The entire collection was utilised to search for varieties resistant and tolerant to RYMV disease. The screening of the collection with different RYMV isolates exposed the susceptibility of most of the accessions in the collection. Most of the O. sativa indica accessions were highly susceptible. However, ten O. glaberrima accessions displayed a delay of symptom expression, and moderate resistance. However, their resistance was overcome later by a particularly virulent RYMV isolate BF1. Remarkably, a single moderately resistant cultivar, BM24, showed that partial resistance and tolerance to RYMV can be found in an O. sativa variety. Serological evaluation of this local variety in comparison with the partially resistant variety, Azucena, showed that BM24 and Azucena expressed similar resistance patterns. A genetic profile of both varieties showed that both had an identical allele status at RM101, which is a marker bracketed in the same zone as the QTL12.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Chikoti, Patrick Chiza. "Development of cassava (Manihot esculenta Crantz) cultivars for resistance to cassava mosaic disease in Zambia." Thesis, 2011. http://hdl.handle.net/10413/8402.
Full textAbstract:
Despite the increasing number of farmers growing cassava in Zambia, yield per hectare has
remained low at 5.8 t ha-1. The major constraints contributing to low yields are pests and
diseases of which cassava mosaic disease (CMD) caused by East Africa cassava mosaic virus
(EACMV), Africa cassava mosaic virus (ACMV) and South Africa mosaic virus (SACMV) is the
most important. Breeding of cassava is restricted by limited information on viruses and
associated satellites, and farmer preferences. Most of the farmers cannot manage to institute
control strategies that require buying of chemicals. The most feasible option remains improving
existing cultivars through resistance breeding. The study therefore was conducted to: i)
establish farmers’ perception and knowledge of CMD; ii) to identify viruses of cassava occurring
in Luapula province; iii) evaluate the performance of local and improved cultivars for agronomic
traits; iv) evaluate the performance of F1 progenies for CMD resistance; and v) determine
general combining ability and specific combining ability for CMD resistance. The studies were
carried out between 2008 and 2011 at different locations in Zambia. The information generated
was important in formulating a local breeding strategy for CMD resistance.
A participatory rural appraisal and a structured survey was conducted in Mansa, Samfya and
Mwense districts in Luapula province involving farmers to ascertain farmers’ perceptions of
CMD. The results of the study showed that the majority of the respondents (97.6%) were not
aware of CMD. Most of the farmers grew landraces on small pieces of land. Although, the
cultivars (local and improved) were widely grown, they were susceptible to CMD. The farmers
preferred cultivars with high yielding and early bulking characteristics among others.
A CMD survey conducted between April and May 2009 in Samfya, Mansa, Mwense,
Kawambwa and Nchelenge districts in Luapula province established East Africa cassava
mosaic virus (EACMV), and Africa cassava mosaic virus (ACMV) as the most prominent viruses
in the area. Symptoms of satellites were also observed in the farmers’ fields in most of the areas
visited. Satellite II and III were detected in leaf samples. The CMD incidence (59.1%) and
severity (2.4) was moderate across the districts surveyed. The CMD symptoms on the cassava
plants were variable with plants showing mild and severe symptoms characterised with
narrowing and reduced leaf blades. The transmission of CMD infections was mainly through
cuttings rather than via whitefly infection which means that most of the planting materials used
by the farmers were infected.
Evaluation of cassava cultivars for CMD resistance was conducted in 2009/2010 and 2010/11
seasons at Mansa Research Station in Luapula province using a 4 x 4 α lattice design. Both
introduced and locally grown cultivars had significant (P<0.001) differences in their reaction to
CMD. Bangweulu, Namuyongo, Kalaba, Chikula, Mwakamoya, Chila7 and Chila11 were the
most susceptible genotypes. Mweru, Tanganyika, and Nalumino were moderately tolerant to
CMD.
Eight hundred F1 genotypes developed using a North Carolina II mating design were evaluated
in a 4 x 5 α lattice design in 2011 at Mansa Research Station, Luapula province to determine
combining ability for reaction to CMD, yield and yield components. The plants were harvested 7
months after planting (MAP). Significant (P<0.001) general combining ability and specific
general combining ability were recorded for CMD. The SCA effects were more important for
CMD than GCA effects suggesting that non-additive gene action was more prominent than the
additive gene action in determining CMD reaction. Parent lines with desired significant, negative
GCA effects for reaction to CMD were Bangweulu, Kampolombo, Nalumino and TME2.
In general, the survey and participatory rural appraisal established CMD as one of the
constraints to cassava production and created a basis for the research study. The findings
indicate opportunities that exist in creating genotypes with tolerance to CMD. The study
identified cassava lines with resistance to CMD. The lines that expressed the above trait should
be selected and tested further for release to the farmers in Zambia. Since the clonal evaluation
trial was harvested at 7 MAP, there is need to investigate further for earliness trait in best
performing lines in different locations.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
50
Chintu, Justus M. M. "Breeding groundnut for resistance to rosette disease and its aphid vector, Aphis craccivora Koch in Malawi." Thesis, 2013. http://hdl.handle.net/10413/10055.
Full textAbstract:
Groundnut (Arachis hypogaea L.) is one of the most important legume crops in Malawi.
However, production among smallholder farmers has declined in recent years. One of the
constraints affecting groundnut production is groundnut rosette disease (GRD). Therefore,
the main objective of this study was to develop appropriate groundnut cultivars that are
resistant to GRD, combined with other traits preferred by farmers, in order to improve
income and food security of smallholder farmers in Malawi and beyond. The specific aims
were; (i) to assess groundnut cropping systems used by smallholder farmers in Malawi, their
varietal preferences, and production challenges (ii) to assess the genetic diversity among
groundnut germplasm collected from ICRISAT, the Chitedze gene bank and farmers (iii) to
identify sources of resistance to GRD and to its aphid vector (iv) and to understand the type
of gene action governing GRD resistance, and to identify groundnut genotypes suitable for
use as parents in breeding for GRD resistance.
Assessment of groundnut cropping systems used by smallholder farmers, their varietal
preferences, and production challenges was done by using a field survey and participatory
rural appraisal (PRA) tools. The field survey was done in Lilongwe, Mchinji and Salima while
the PRA was done in Kasungu, Lilongwe, and Salima. The assessment of genetic diversity
among 106 groundnut genotypes collected from ICRISAT, Chitedze gene bank and farmers
was done using 19 SSR markers. High throughput DNA extraction was done followed by
polymerase chain reactions (PCR) after which the amplified products were analyzed.
Evaluation of genotypes to identify new sources of resistance to GRD and its aphid vector
was conducted under two test situations, one with high inoculum levels and one with low
inoculum levels. Under high inoculum level, the infector row technique developed by Bock
and Nigam (1990) which employs a susceptible variety as a disease spreader was used.
While under low inoculum level, an aphid resistant variety instead of the infector row was
used to control the aphids. Aphid resistance was studied under field and glasshouse
conditions. Plants were planted in rows and at 14 DAS, 2 aphids were place on each plant.
Aphid resistance was determined by observing the increase in number of the aphid
population on the test plants. Gene action governing inheritance of resistance to GRD was
studied under high disease pressure created by using viruliferous aphids. Parents and F2
generations and their reciprocals were used in the study. The trials were laid out in a
glasshouse and aphids were infested a week after germination and were killed after 7 days
using Dimethoate. Disease data was collected at 7, 14, 21 and 28 days after aphid
infestation.
The study on groundnut cropping systems, varietal preferences and production challenges
revealed that most farmers grew groundnut alongside maize (Zea mayis L.) and beans
(Phaseolus vulgaris L.) as food crops and tobacco (Nicotiana tabacum L.) and cotton
(Gossypium hirsutum L.) as cash crops. The most preferred groundnut varieties grown by
farmers were Chalimbana and CG 7. GRD was observed in half of the fields visited.
However, 98% of the farmers interviwed had experienced it in their fields at some point, and
63.3% of the farmers believed that GRD was a major problem. Other challenges noted by
farmers included lack of quality seed, poor extension support, lack of inputs, manipulation of
the markets by buyers, and the failure of groundnut crops to meet the high standards
required by the market. The examination of genetic diversity among 106 groundnut
genotypes revealed a total number of 316 alleles with a mean of 17 alleles per locus.
Polymorphic information content (PIC) and gene diversity values were high, which indicated
that genetic diversity among the groundnut genotypes was high. The analysis of molecular
variance indicated that 72.9% of the genetic variation observed in the genotypes was due to
the variation between individuals within rather than between specific population groups. The
evaluation of genotypes for resistance to GRD revealed five highly resistant genotypes
namely ICG 9449, ICG 14705, ICGV-SM 05701, MW 2672 and MW 2694. Farmer preferred
genotypes were rated as either moderately resistant or susceptible to GRD. Aphid resistance
was only recorded in ICG 12991. Yield and GRD incidence were negatively and moderately
correlated, which confirmed that GRD has the potential to reduce yield in groundnuts. The
highly resistant genotypes were also high yielding except for genotype ICG 9449. Farmer
preferred genotypes CG 7, Chalimbana and Tchayilosi, also gave above average yields,
despite high disease incidence levels, which showed that these genotypes have tolerance to
GRD. The study on gene action governing GRD resistance revealed information on
combining ability effects of GRD resistance. The diallel analysis showed that GCA, SCA,
reciprocal, maternal and non-maternal effects were all significant, which indicated that both
additive and non-additive gene effects played a role in governing GRD resistance. The
significance of SCA and reciprocal effects indicated that maternal parents played an
important role in the expression of GRD resistance. However, the additive effects were
predominant over non-additive gene effects. Four of the resistant genotypes, ICG 14705,
MW 2694, ICGV-SM 05701, and MW 2672, were the best combiners for GRD resistance.
Generally, the study indicates that there is still a need to develop new varieties with
resistance to GRD having traits preferred by farmers to enhance adoption. There is also a
need for breeders to work with extension staff in promoting new varieties and also there is
need for extension staff to actively provide information to farmers on production and
marketing of groundnut. Groundnut is widely known to have a narrow genetic base which
has been a bottleneck to its improvement. However, the high genetic diversity observed in
this study provides a basis for selection of appropriate parental genotypes for breeding
programmes which can enhance further the broadening of the groundnut genetic base.
Identification of the genotypes with high resistance to GRD in this study provides an
opportunity to breed more GRD resistant materials. The observation that additive gene
effects are predominant in governing GRD resistance means that GRD resistant materials
can be improved by introgressing additive genes using recurrent selection breeding
procedures. There is also a need to employ molecular techniques which can help in
shortening the entire breeding process.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.