Letteratura scientifica selezionata sul tema "South african sunflower seed"

Sunflower (Helianthus annuus L.) recently was reintroduced to Mozambique because of renewed interest in oil-seed production for domestic consumption. In April 1997, disease surveys were carried out in two fields in southern Mozambique (Maputo region). Several plants of Pan 735, a South African cultivar, showed yellowing of the leaves and stunting. These plants wilted during the day but recovered their turgidity at night. Diseased plants were easily pulled from the soil due to almost complete destruction of the root system. Numerous galls were found on affected roots, compared with healthy plants. Meloidogyne javanica (Treub) Chitwood and M. incognita (Kofoid & White) Chitwood were identified by M. Di Vito (personal communication) based on 20 female perineal patterns observed with a light microscope. M. incognita was more prevalent than M. javanica. Also observed were Alternaria helianthi (Hansf.) Tubaki & Nishihara and Sclerotium bataticola Taub. Root-knot nematodes (Meloidogyne spp.), common on sunflower, cause severe damage and reduce both seed yield and seed oil content (1). These two nematode species have also been observed on sunflower in other African countries (Zambia, South Africa, Egypt) but this is the first report of root-knot nematode on sunflower in Mozambique. Reference: (1) M. Di Vito et al. Nematol. Medit. 24:109, 1996.

The paper presents the results of a study that estimated the demand relations for primary oilseeds in South Africa. The Error Correction version of Linear Approximated Almost Ideal Demand System (LA/AIDS)(ECM-LA/AIDS) were estimated. Time series data for the period 1971-2002 were analysed. Prior tests stablished weak searability between four oilseeds (sunflower seed, soybeans, groundnuts and cotton seed), indicating that these oilseeds should be modelled together. The results suggest that the demand for oilseeds is negatively influenced by own price, which is consistent with economic theory, while positive long-term expenditure elasticities suggest that some oilseeds, notably sunflower seed and cotton seed, are luxury commodities in South Africa.

White rust of sunflower (Helianthus annuus L.), caused by Albugo tragopogonis (Pers.) S. F. Gray, appeared in South African fields not previously planted to sunflower. Spread to these fields from infested fields was unlikely, as some of the newly affected fields were planted out of season and were more than 300 km away from other sunflower production fields. Several reports of this nature led us to investigate the possibility of seed transmission of the causal organism. Extensive colonization of sunflower heads by A. tragopogonis was observed in field trials and breeding nurseries. Head infections consisted of two distinct lesion types. White rust pustules, typical of those formed on abaxial sides of leaves, were recognized on abaxial sides of involucral bracts. Grayish, localized lesions containing dark-colored oospores of the fungus, similar to those formed on stems and petioles (1), were produced in sub-epidermal tissue and extended 3 to 5 mm deep into receptacles. Colonization of seeds was found in only a few lines. Oospores were produced in the pericarps and testae of seeds. No oospores or hyphae, however, were observed in the embryo. This is the first report of A. tragopogonis being seed-borne. Since the incidence of seed infection is low, spread of disease to infested fields is expected to be insignificant. Of more concern, however, is the possible long-range dissemination of the fungus by means of infected seed into regions or countries where the disease has not been previously reported. Reference: (1) P. S. Van Wyk et al. Helia 18:83, 1995.

Downy mildew, caused by Plasmopara halstedii (Farl.) Berl. & De Toni in Sacc., is an economically important disease of sunflower (Helianthus annuus L.) in Europe and the United States (1). The disease was first noticed in South Africa in a commercial field near Standerton and in a seed production field near Kroonstad during the 1993 to 1994 planting season. During the 1995 to 1996 season, downy mildew was found in experimental hybrids near Heilbron, and in commercial fields near Heil-bron, Marikana, and Potchefstroom. At Heilbron, five hybrids were infected with P. halstedii, whereas three others showed symptoms of downy mildew at Potchefstroom and Marikana. All commercially cultivated hybrids have been developed in South Africa. Disease incidence in all the fields was low, with less than 1% of plants affected by the disease. Diseased plants were dwarfed and displayed veinal chlorosis of leaves typically associated with downy mildew of sunflower. White fungal growth commonly occurred on lower leaf surfaces. Sunflower seedlings inoculated with P. halstedii produced symptoms characteristic of downy mildew. The occurrence of the disease in many geographic areas and on various hybrids in South Africa suggests that the fungus is well established. Recent outbreaks can be attributed to the cool, wet, climatic conditions of the 1993 to 1994 and 1995 to 1996 seasons. The susceptibility of local hybrids suggests that downy mildew is a potentially dangerous disease of sunflower in South Africa. Reference: (1) J. F. Miller and T. J. Gulya. Crop Sci. 27:210, 1987.

Insights into plant endophytic microbes and their exploration in agriculture have provided opportunities for sustainable plant health and food safety. Notable endophytic Bacillus species with plant growth-promoting traits have been documented; nevertheless, information on genome analysis of B. cereus associated with the sunflower in South Africa has not been studied. Therefore, we present whole-genome sequence of agriculturally important B. cereus strain T4S isolated from sunflower plants. The NextSeq Illumina sequencing yielded 7,255,762 bp sequence reads, 151 bp average read length, 5,945,881 bp genome size, 56 tRNA, 63 rRNA, and G + C content of 34.8%. The phylogeny analysis of strain T4S was similar to B. cereus NJ-W. Secondary metabolites, such as petrobactin, bacillibactin, bacitracin, molybdenum factor, zwittermicin, and fengycin underlining bacterial biocontrol efficacy against phytopathogens were found in the T4S genome. The predicted novel genes in the bacterial genome mediating the complex metabolic pathways can provide a genetic basis in understanding endosphere biology and their multiple functions thereof in crop improvement. Interestingly, seed and root inoculation with strain T4S contributed to sunflower yield under greenhouse experiments. Hence, the detection of notable genes specific for plant growth promotion as validated under in vitro screening, promisingly, suggests the relevance of strain T4S in agricultural biotechnology.

Seed yields and oil contents were determined for several sunflower cultivars grown in the south-east of South Australia over a range of environments which included different locations and years. Data were analysed by modified joint regression techniques. Each cultivar was included in at least four experiments to allow analysis by modified joint regression. The highest seed yields were produced by Hysun 3 1, Sungold, Suncross 52, Sunking and Hysun 30, which produced 16.4, 15.4, 14.7, 12.4 and 7.4% more seed, respectively, than Peredovik. Seeds with the highest oil contents were produced by Suncross 52 (48.6% w/w) and Hysun 31 (48.3%); Hysun 10 and Stepniak produced seeds with the lowest oil content (43.7 %) . Later flowering cultivars had significantly higher seed yields and oil contents than earlier flowering cultivars, indicating that they were better adapted to the environment. For every day that flowering of a cultivar was later than that of Perodovik, mean seed yield increased by 56.6 kg/ha and oil content by 0.4%.

Thesis (M. Tech. Agriculture) -- Central University of Technology, Free state, 2012
A series of incubation studies and greenhouse experiments were conducted to evaluate the use of EM seed treatments, at different application levels, handling techniques and soil conditions on germination and seedling vigour of selected cultivars of maize, sorghum and sunflower. Two incubation studies were conducted to evaluate the germination and seedling vigour of maize, sorghum and sunflower seeds treated with M-EM from three different suppliers, multiplied at two different ratios (1% and 3%) and diluted at three different levels (0.01%, 0.1% and 1.0%) compared to a control treated with pure water. Results revealed no significant differences under optimum germination conditions, while seedlings under cold stress indicated that M-EM treatments positively affected germination and seedling vigour compared to the control treatments. Two incubation studies were also conducted to evaluate the germination and seedling vigour of maize, sorghum and sunflower seeds treated with M-EM from three different suppliers, multiplied at two different ratios (1% and 3%) and exposed to the influences of irradiation and temperature fluctuation. From the results became clear that the correct storage and handling is essential in optimizing the effect of M-EM on seeds. Even though M-EM was exposed to irradiation and temperature fluctuation, M-EM still had positive effects on germination and seedling vigour. Pot experiments were conducted to determine the effect of EM as seed treatment, at different dilutions, on germination, seedling vigour and dry mass of maize, sorghum and sunflower at different planted depths. Germination were not affected by the M-EM treatment, while shoot length results indicated that seed treated with M-EM could have significant effect on seedling survival. A greater effect was visible on the shoot length of shallow planted seeds, than on deeper planted seeds. From the results no single company, ratio or dilution could be prescribed as paramount. To further investigate the effect of M-EM subjected to the influences of irradiation and temperature fluctuation; maize, sorghum and sunflower seeds were treated with M-EM from three different suppliers, multiplied at two different ratios (1% and 3%) and exposed to the influences of irradiation and temperature fluctuation and planted in soil. M-EM treatments only benefited the germination of deeper planted sorghum seeds compared to the control treatments. The shoot lengths of deeper planted maize and sunflower seed were positively increased by the M-EM treatments while also resulting in significant results for the overall shoot length of sorghum. The third pot study was conducted to determine the influence of EM as a seed treatment on maize, sorghum and sunflower planted in three different soils, namely: sterilized soil, soil treated with M-EM and Fusarium containing soil. Germination and seedling vigour results of the sterilized and M-EM treated soil revealed to be superior to that of the Fusarium containing soil. From the results was concluded that M-EM treatments will probably improve early seedling growth of maize, sorghum and sunflower compared to untreated seed and that M-EM seed treatment and a pre-plant EM soil treatment might assist seeds in unfavourable germination and growth conditions.

Thesis (MPhil)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: This study (Seed politics: An exploration of power narratives in the South African seed industry) attempts to unravel the contradictory power relations shaping South Africa’s seed system and to explore spaces of system intervention that could allow alternate seed systems to emerge. As a base for the agricultural sector, the seed system plays an important role in determining the type, quality and cost of seed supplied to the country’s farmers. By extension then, it also partly determines the type, quality and, to some extent, the cost of food sold to the country’s citizens. Ownership of seed germplasm, protected through plant breeders’ and intellectual property rights, is a contentious, current issue. Debate on international and national levels focuses on possible health issues related to consumption of genetically modified food, ethical considerations around ownership of plant life, monopolisation of seed markets, and the implications of biodiversity loss for food security and climate change adaptation. The first article (Contesting the credibility of consolidation of the South African seed industry) examines how historic and current power relations (on a global and local level) have shaped the ‘modernistic’ direction of South Africa’s seed system, which is now dominated by two US-based multinational companies. The contradictions between this direction and state policy are highlighted, focusing particularly on issues of food security, biodiversity and climate change. Article 2 (Imagining a sustainable South Africa seed system) unpacks the assumptions on which the current system is based, in order to provide space for a new ‘narrative’ around seeds to emerge, motivating for a collaborative ‘imagining’ of a sustainable seed industry, based on a social learning approach. Points of system intervention are suggested and expanded on. In both articles, the complexity of seed systems is outlined providing a framework for understanding the interconnectedness of system elements, intervention points and potential for non-linearity. The study weaves together theory drawn from a diversity of themes to expose how the ‘hidden’ faces of power (entrenched in economic hierarchies and institutions) predetermine the path of the system and whom it benefits and whom it excludes. These themes include economics of consolidation, innovation theories, patenting issues, South African policy documents, international treaties and agreements, systems theory and complexity thinking, social learning, industrial and agro-ecological farming methods, agricultural productivity, and climate change. The study promotes social learning as a tool that could unlock the potential of the seed system to contribute to the urgent issues South Africa faces around biodiversity loss, food insecurity and climate change. Keywords: seed system, genetically modified and hybrid seed, seed patents, seed innovation, social learning, systems theory, complexity thinking, consolidation of seed industry.
AFRIKAANSE OPSOMMING: Hierdie studie (Saadpolitiek: ʼn ondersoek van magsnarratiewe in die Suid-Afrikaanse saadbedryf) poog om die teenstrydige magsverhoudinge wat vorm aan die Suid-Afrikaanse saadstelsel gee, uit te pluis en ruimtes van stelsel-intervensie wat die opkoms van afwisselende saadstelsels moontlik kan maak, te ondersoek. As grondslag van die landbousektor speel die saadstelsel ʼn belangrike rol in die bepaling van die soort, gehalte en koste van die saad wat aan die land se boere verskaf word. Dus bepaal dit ook deels die soort, gehalte en, in ʼn sekere mate, die koste van die voedsel wat aan die land se burgers verkoop word. Eienaarskap van saadkiemplasma, wat deur planttelersregte en regte op intellektuele eiendom beskerm word, is ʼn omstrede en aktuele kwessie. Debatvoering op sowel internasionale as nasionale vlak fokus op moontlike gesondheidskwessies wat verband hou met die inname van geneties gemodifiseerde voedsel, etiese oorwegings ten opsigte van eienaarskap van plantlewe, monopolisering van saadmarkte, en die implikasies van die verlies aan biodiversiteit op voedselsekerheid en aanpassing by klimaatsverandering. Die eerste artikel (Betwisting van die geloofwaardigheid van die konsolidering van die Suid-Afrikaanse saadbedryf) ondersoek hoe historiese en huidige magsverhoudinge (op sowel globale as plaaslike vlak) die ‘modernistiese’ rigting van die Suid-Afrikaanse saadstelsel, wat nou deur twee multinasionale maatskappye in VSA-besit oorheers word, gevorm het. Die teenstrydighede tussen hierdie rigting en regeringsbeleid word uitgelig, en daar word in die besonder gefokus op die potensiële invloed op voedselsekerheid, biodiversiteit en die kapasiteit om by klimaatsverandering aan te pas. Artikel 2 (‘n Veronderstelling van ʼn volhoubare Suid-Afrikaanse saadstelsel) ondersoek die aannames waarop die huidige stelsel gegrond is, ten einde plek te maak vir ʼn nuwe ‘narratief’ oor saad, motivering vir ʼn medewerkende ‘veronderstelling’ van ʼn volhoubare saadbedryf, gegrond op ʼn benadering van sosiale leer. Punte van stelsel-intervensie word voorgestel en op uitgebrei. In albei artikels word die kompleksiteit van saadstelsels uitgestippel ten einde ʼn raamwerk te bied waarvolgens die onderlinge verband van stelselelemente, intervensiepunte en die potensiaal vir nie-lineariteit begryp kan word. Die studie verweef teorie vanuit diverse temas ten einde bloot te lê hoe die roete van die stelsel, asook wie daaruit voordeel trek en wie daardeur uitgesluit word, vooraf deur die ‘versteekte’ aangesigte van mag (verskans in ‘stelselgeheue’ en bekragtig deur instansies) bepaal word. Hierdie temas sluit in die ekonomie van konsolidasie, innoveringsteorieë, patentkwessies, Suid-Afrikaanse beleidsdokumente, internasionale verdragte en ooreenkomste, stelselteorie en kompleksiteitsdenke, sosiale leer, industriële en agro-ekologiese boerderymetodes, landbouproduktiwiteit en klimaatsverandering. Die studie bevorder sosiale leer as ʼn hulpmiddel wat die potensiaal vir die saadstelsel om tot die dringende uitdagings vir Suid-Afrika ten opsigte van die verlies aan biodiversiteit, voedselonsekerheid en klimaatsverandering by te dra, kan ontsluit. Sleutelwoorde: saadstelsel, geneties gemodifiseerde saad, hibriede saad, saadpatente, saad-innovering, sosiale leer, stelselteorie, kompleksiteitsdenke, konsolidasie van saadbedryf.

This study provides an overview of the sunflower seed industry, globally and locally. This overview is, followed by measurements of the comparative and competitive advantages of the South African and Argentinean sunflower seed industries. Two indexes are used to calculate the comparative and competitive advantages namely the Revealed Comparative Advantage (RCA) and the Relative Revealed Comparative Trade Advantage (RTA) index. The results show that South African sunflower seed has a competitive advantage in their primary form, however the value added sunflower seed products show a competitive disadvantage which is opposite to that of Argentina’s sunflower seed products. The finding that South Africa is only competitive in the primary sunflower seed market was calculated by means of trade data. Factors that affect the competitiveness of the sunflower industry were identified to indicate why value added sunflower seed products experience a competitive disadvantage. In the analysis it was found that the South African sunflower industry is price driven. Since price plays an important role in the competitiveness of the industry, imports of cheaper sunflower crude and refined oils are considered to pose a major threat to the industry. Crushing margins has increased over the last few years due to higher sunflower oil and sunflower oilcake prices. In order to increase the competitiveness of the South African sunflower seed industry, it needs to; be more cost competitive; improve quality; launch new products; invest in new technologies and improve the innovativeness. Emphasis should be placed on the value added seed products as this is where South Africa has a competitive disadvantage. Health issues are of great importance to the local as well as global market and the production of a healthier vegetable oil has become a necessity for this industry. Innovation in this commodity will lead to great improvement in the competitiveness of the sunflower seed industry. Investment towards research and innovation is necessary in order to keep up with the changing environment. The competitiveness of the sunflower seed industry in South Africa cannot be achieved without the help of the government. Policy issues must be put in place to avoid the dumping of cheaper crude vegetable oils as well as bottled cooking oils in South Africa.
Thesis (M.B.A.)--North-West University, Potchefstroom Campus, 2012.

Thesis (MScAgric)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: African Acacia species are often major contributors to the progressive increase in the woody component of savannas, a phenomenon commonly referred to as bush encroachment. In Hluhluwe- Umfolozi Park, the numbers of adult Acacia nilotica (L.) Willd. Ex Del. trees per hectare far exceed (by III) that of A. karroo Hayne adults. The relative dominance is reversed in the juvenile stage with A. karroo (725 ha') outnumbering A. nilotica (225 ha-I) threefold outside closed woodlands. African acacias produce large quantities of seed and may have large soil-stored seed banks. They suffer pre-dispersal predation by bruchid beetles and may be either wind or animal dispersed. Once dispersed they are vulnerable to post-dispersal attack. This study tested several hypotheses regarding various aspects of seed ecology of A. karroo and A. nilotica. The null hypothesis that seed ecology does not contribute to the success of A. karroo over A. nilotica, was tested. Acacia karroo trees were smaller (mean basal diameter: 7.8 cm) than A. ni/otica trees (mean basal diameter: 18.5 cm) on average, but produced more seeds (A. karroo mean: 1628; A. nilotica mean: 992) for a given basal diameter size class. It was found that A. karroo showed less bruchid infestation (mean: 1.36-3.81%) than A. nilotica (mean: 14.67-86.70%) at all stages of pod development with a proportion of A. karroo seeds (7.1 %) being able to germinate after bruchid attack. Bruchid attack rendered A. ni/otica seeds unviable. There was no difference between the two species with regards to the soil-stored seed bank and the viability of seeds found in the soil. Acacia karroo showed higher germination levels (5.1%) and better establishment (4.9%) than A. nilotica (1.5% and 0.4% respectively). On average, there was no difference in germination levels between burnt and unbumt seeds, but there was a significant difference in germination of burnt seeds in both burnt (4.5%) and unbumt (2.5%) sites and unbumt seeds in both burnt (2.8%) and unbumt (4.9%) sites when considered separately. Post-dispersal predation of A. karroo seeds (21.8%) was higher than that of A. nilotica (12.7%). There was more rodent predation in tall grass areas (26.0%) than short grass (10.7%) or canopy areas (15.2%), and most seeds were lost from unprotected control groups. Rodent presence was a significant factor in unexplained seed disappearance. The ability of A. karroo to germinate easily and the low levels of beetle predation experienced by this species seemed to be its main advantage over A. nilotica as an encroaching species in Hluhluwe-Umfolozi Park.
AFRIKAANSE OPSOMMING: Die Acacia spesies van Afrika is dikwels belangrike bydraers tot die progressiewe toename in die houtkomponent van savannas. Hierdie verskynsel word algemeen na verwys as bosindringing. In die Hluhluwe-Umfolozi Park is die aantal volwasse Acacia nilotica (L.) Willd. Ex Del. bome per hektaar aansienlik meer (l l l meer) as die aantal volwasse A. karroo Hayne bome. In die jong stadium is die oorheersing omgekeerd, met driekeer soveel A. karroo (725 ha-I) as A. nilotica (225 ha-I) bome buite beboste gedeeltes. Afrika se Acacia spesies produseer groot hoeveelhede saad en kan oor aansienlike grond-gebergde saadbanke beskik. Voor verspreiding word die saad aan predasie deur bruchid-kewers blootgestel. Die saad kan óf deur wind óf diere versprei word en na verspreiding word dit ook aan predasie blootgestel. Hierdie studie het verskillende hipoteses rakende verskeie aspekte van die saadekologie van A. karroo en A. nilotica getoets. Die nulhipotese dat saadekologie nie tot die groter sukses van A. karroo teenoor A. nilotica bydrae nie, is getoets. Acacia karroo bome was oor die algemeen kleiner (gemid. basale omtrek: 7.8 cm) as A. nilotica (gemid. basale omtrek: 18.5 cm) bome maar het meer saad (A. karroo gemid.: 1628; A. nilotica gemid.: 992) per gegewe basale diameter grootte klas gelewer. Daar is geen verskil tussen die twee spesies rakende grondgebergde saadbanke en die lewensvatbaarheid van hierdie saad gevind nie. Acacia karroo het hoër vlakke van ontkieming (5.1%) en beter vestiging (4.9%) as A. nilotica (l.5% en .4% respektiewelik) getoon. Daar was oor die algemeen geen verskil in die ontkiemingsvlakke van gebrande en ongebrande sade nie, maar wel 'n beduidende verskil in die ontkieming van gebrande sade in beide gebrande (4.5%) en ongebrande (2.5%) areas en ongebrande sade in gebrande (2.8%) en ongebrande (4.9%) areas as dit afsonderlik geëvalueer is. Die predasie van A. karroo saad na verspreiding (21.8%) was hoër as dié van A. nilotica (12.7%). Daar was meer knaagdier-predasie in gebiede met lang gras (26.0%) as dié met kort gras (10.7%) of boomryke gedeeltes (15.2%). Die meeste saad is in onbeskermde kontrolegroepe verloor. Die teenwoordigheid van knaagdiere het 'n belangrike rol in die onverklaarde verdwyning van saad gespeel. Dit is gevind dat A. karroo se vermoë om maklik te ontkiem, asook die lae vlakke van insek skade aan die saad, die belangrikste voorsprong is wat dié spesie oor A. nilotica as 'n indringer in Hluhluwe-Umfolozi Park het.

Includes bibliographical references
Seed dispersal is a key process. It is important in plant population biology because it influences the fate of seeds and the probability of recruitment, in plant biogeography since dispersal mode can influence the distribution range and rate of response to environmental change and habitat fragmentation, and in animal ecology since fruits can be an important dietary item (Wang and Smith, 2002). The majority of trees in the tropics (70 – 90%) and a large proportion of trees in temperate regions (up to 60%) rely on vertebrates for their dispersal (Howe and Smallwood, 1982; Fleming et al., 1987, Willson, 1990). Vertebrate dispersers range in size from 5g mistletoe birds (Dicaeidae) to 7,500,000g elephants (Elephantidae). The range and distribution of frugivore sizes is not uniform across ecosystems or geographical regions (Mack, 1993). These differences, one might suspect would be mirrored in the range and distribution of fruit size. This is not the case; in South America where the largest frugivorous mammal is the tapir (300kg; Hansen and Galetti, 2009), there is a subset of fruit that are conspicuously large. The paradoxical existence of such large fruit in the lowlands of Costa Rica was first noted by Janzen. In collaboration with Pleistocene faunal expert Paul Martin they conjectured that these fruit were ecological anachronisms that had evolved in the presence of large terrestrial vertebrates (>1000kg - megafauna) but had remained long after their demise (Janzen and Martin, 1982).

Fire is generally used as a management tool for different vegetation types such as savannas and grasslands in southern Africa. In the False Thornveld of the Eastern Cape, fire is commonly used to control bush encroachment and to increase grass production, as grasses are important source of forage for domestic livestock. At the University of Fort Hare farm in the Eastern Cape, a trial was set up in 1980 to investigate the effect of burning frequency on vegetation. There are six treatments replicated twice in a completely randomized design on a 100 m x 50 m plots. The treatments comprise no burn, annual, biennial, triennial, quadrennial and sexennial burns. From this trial a study was conducted to investigate long term effect of burning frequency on species and soil seed bank diversity. Two 100 m line transects located 25 m apart were laid within each plot, and the herbaceous and woody species were identified and recorded along the line transects. Relative abundances (%) for each species were calculated for each treatment. Soil samples were collected at an interval of 13.3 m along the line transects. The samples were placed in paper bags and kept for use in a germination experiment. The seedling emergence germination method was used in the glasshouse to determine emerging seedlings, pots were filled with Hygromix growth medium and the soils from the fire trials 12 X 6 = 72 were spread on top. Soil from the control plots were also pre-treated with heat, smoke and the combination of heat and smoke. The experiment started in January 2010 and was terminated in April 2010. The Shannon-Weaver Diversity Index was used to determine species diversity for standing vegetation and germinated seedlings. Data were tested for normality and species abundances were transformed. Analysis of Variance (ANOVA) was applied to test treatment effects on geminated seedlings, species abundance and diversity at α = 0.05 significance level. Significant differences between treatment means were determined by post v hoc tests using Fischer‟s Least Significant Difference test at α = 0.05. The Pearson Moment Correlation test was used to test the relationship between vegetation and soil seed banks. Treatments had significant effects on herbaceous, woody species abundance and diversity (P < 0.05), but there was no significant treatment effect on soil seed bank diversity and on pre-germination treatments (P > 0.05). The annual, biennial and triennial burns were dominated by Themeda triandra while the quadrennial, sexennial and the control treatments were dominated by Sporobolus fimbriatus and Melica decumbens. A. karroo dominated the woody component across all treatments, but it did not change in abundance. S. fimbriatus was the most abundant in the soil seed bank across all the treatments and also in all pre-germination treatments. Species diversity was high in standing vegetation in the quadrennial, sexennial and the control treatments. There was no significant correlation between the standing vegetation and soil seed bank diversities (P > 0.05). Based on these findings it is apparent that fire can change vegetation in an area to be dominated by fire tolerant or fire intolerant species. Fire frequency, heat and smoke affects soil seed banks to a lesser extent in the False Thornveld. For the management of the False Thornveld of the Eastern Cape, less frequent burning is recommended as it increases aboveground species diversity.

Sunflower is the most important oilseed crop in South Africa and accounts for approximately 60 % of all oilseeds produced locally. The primary by-products of the sunflower seed crushing industry provides high-value inputs towards the food and animal feed manufacturing sector in the form of edible oil and protein meal. Prior to 1996, the South African sunflower seed complex market was controlled by the Oilseed Board, which operated a single-channel pool scheme and regulated the marketing of oilseeds and oilseed products. Since the liberalisation of the South African agricultural sector, role-players have been fully exposed to the dynamics and risks of the international oilseed complex market. Over the years participants in the agricultural commodity markets have developed various instruments to assist them in their decision-making process – one of them being commodity modelling, which is described as a methodological technique that provides a powerful analytical tool for examining the complexities of commodity markets. In South Africa, many role-players in the various agricultural industries make use of a multi-sector commodity level partial equilibrium model better know as the BFAP sector model which is maintained by the Bureau for Food and Agricultural Policy (BFAP) at the University of Pretoria. The objective of this study was to expand the coverage of the existing BFAP sector model by developing a comprehensive system of equations for the total sunflower seed complex, which includes not only a partial equilibrium model for sunflower seed, but also sunflower oil and cake. In this study much emphasis was not only placed on the formation of prices of the various products, but also the application of the most suitable model structures in order to trace the behaviour of the various prices under real market conditions as accurately as possible. This study applied the methodology developed by the Food and Agricultural Policy Research Institute (FAPRI) and further adapted by the Bureau for Food and Agriculture Policy (BFAP) to develop the partial equilibrium model of the South African sunflower complex. The single equations were estimated by mainly using ordinary least squares (OLS), but in cases where the results of the OLS were contradictory to the theory or where insufficient data was available, calibration techniques were employed and the equations were synthetically constructed. The constructed model was applied to lay down a baseline projection for the total production and consumption blocks of sunflower seed, oil and oilcake. The baseline projections also formed part of the ex post validation of the model’s performance. Finally the consistency of the model was evaluated in the form of scenario analysis. Various real-world market- and policy-related shocks were imposed and the results were compared to the baseline projections. In general the model developed in this dissertation performed well and can be used to analyse the effects of economic, technological and policy changes on the South African sunflower seed complex. It also provides a sound structure for the development of a complete South African oilseed complex model that includes soybeans, canola, groundnuts, cotton and imported palm oil. Copyright
Dissertation (MScAgric)--University of Pretoria, 2010.
Agricultural Economics, Extension and Rural Development
unrestricted

Sunflower (Helianthus annuus L.) is one of the most important oil crops in South Africa and genetic improvement for grain yield and oil-content was initiated in the country in the early 1970s. Commercial production of sunflower in South Africa is done under natural rainfall conditions in areas where frequencies of drought are high hence the requirement for drought tolerant cultivars. An assessment of the genetic gains in seed and oil yield achieved since 1970, the effects of re-cycling inbred lines and strategies for developing drought tolerant sunflower cultivars has not been done for South African sunflower breeding programmes. Two data-sets were used for the genetic gain studies: side-by-side evaluation of historical and current sets of popular cultivars in the same environment under one set of trial management practices; and yield trends in commercial farmers’ fields based on annual production estimates. The estimated relative genetic gain for seed yield based on side-by-side trials was 1.5% year−1 and the relative gain in seed yield per year under commercial production was 1.9% year−1. The contribution of new cultivars to total seed yield progress in sunflower were 56.3% for the period 1970 to 1989; 23.9% from 1990 to 2009 and the mean over the four decades under consideration from 1970 to 2009 was 41.6%. Quantifying the usefulness of inbred lines in advanced cycle plant breeding was done using four base breeding populations based on: phenotypic or genetic variability; heterosis; and combining ability. Significant genetic variation was evident for seed yield and oil yield while genetic variability for oil content was low. Genetic advance (GA%), with a 10% selection intensity, was high for seed yield and oil yield for each of the four populations ranging from 36-42% and 38-43%, respectively. The GA% for oil content was low ranging from 1.3% to 5.1% indicating the need to introgress high oil content germplasm in the present breeding populations in advanced cycle pedigree breeding. Founder parent heterosis (FPH), mid-standard heterosis (MSH) and high standard heterosis (HSH) indicated that some new testcross hybrids from the advanced cycle pedigree breeding populations were performing better than their founder parents in hybrid combination as well as the standard commercial hybrid checks. From variance component analysis, general combining ability (GCA) was predominant over specific combining ability (SCA) for seed and oil yields indicating that superior hybrids can be identified based on positive and significant GCA effects of the female lines. For oil content, SCA was predominant over GCA indicating that it would be best to select for specific hybrids combinations with high oil content rather than selecting female lines with high GCA effects. Variable moisture conditions characterise the sunflower production environments in South Africa. Breeding for such environmental conditions requires a combination of strategies including use of secondary traits and developing appropriate test environments. Three secondary traits, head diameter, stem diameter and stay green canopy which are easy to measure in the field were evaluated for their appropriateness for selecting for drought tolerance under three moisture conditions: random stress environments (RSE), managed drought stress environments (MSE) and well watered nonstress environments (NSE). Type A genetic correlations indicated that stay green canopy (SG) had the potential to be used as secondary trait to indirectly improve oil yield under the three moisture conditions. The indirect selection efficiency (ISE) for SG using genetic correlations based on H2 were 0.79, 0.82 and 0.78 in the RSE, MSE and NSE, respectively, while that using genetic correlation based on h2 were 0.67, 0.98, and 0.93 in the RSE, MSE and NSE, respectively. In both cases selection in the MSE had the highest efficiency using genetic correlations based on either H2 or h2. Estimates of indirect selection based on type B genetic correlations indicated that indirect selection for oil yield (OY) in the MSE and NSE for the target RSE was as effective as direct selection of OY in the RSE based on additive genetic correlations of 0.96 obtained in both selection environments. Overall, the results from the exploratory drought tolerance study should inform the development of breeding strategies to improve drought tolerance and associated yield stability of sunflower cultivars grown in South Africa and associated environments.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Disa comprises 163 species, 131 of which occur in South Africa (SA). The genus is distributed across winter- and summer-rainfall areas, but few species transverse both climatic regions. Species are therefore regarded as winter-rainfall or summer-rainfall endemics - yet release their seeds in autumn, irrespective of provenance. Disa contributes 40 % of threatened Orchidaceae in SA, with half of the local species requiring conservation initiatives. In vitro seed germination is a potential conservation tool for producing large numbers of genetically diverse plants in relatively short periods. However, only 11 winter-rainfall Disa species are easily germinated ex situ. Studies were therefore undertaken on summer-rainfall taxa, which are ungerminated in vitro, in an effort to define their germination parameters. This thesis describes mechanisms that control germination in Disa and establishes practical propagation methods for seed culture. Two seed types occur in Disa; i) comparatively large, pale and pyriform seeds in members of the D. uniflora sub-c1ade, which populate streamside habitats under conditions of winter-rainfall maxima, and ii) smaller, variously brown and fusiform seeds in the remainder of the genus. Seed morphometrics distinguished seed types, although embryo dimensions were similar. Testa continuity, which is disrupted in the large seeds, also supported separation. Typically, small seeds are ungerminated in vitro, whilst large seeds germinated readily. Increased seed size did not necessarily impart increased germ inability, as several germinable, small-seeded species exist - being winter-rainfall species Attempts to establish in vitro germinability revealed that increased water availability and charcoal supplementation promoted germination in intractable species. The control of germination was therefore proposed as a trade-off between water availability and the presence of phyto-inhibitors - two features typical of seeds exhibiting water-impermeable dormancy. Three germinability categories were recognized; i) easily germinable species, ii) poorly germinable species through media manipulation, and iii) ungerminated species. Germination of immature seed in the absence of media modification was comparable to mature seed germination under modified conditions, providing evidence of the role of an impermeable seed testa in regulating germination. Testa impermeability in mature, small-seeded species was demonstrated using aqueous EVANS' blue dye and was linked to i) testa integrity and ii) increased levels of leachable phenolics (LPC) - which are hydrophobic and phytotoxic. In addition, this research revealed an impervious and elaborate embryo carapace in small seeds. Large-seeded species were highly permeable at dehiscence, with perforated testae and negligible LPC. Germinability was ultimately defined by a significant regression with LPC. Phenolic deposition increased exponentially with increasing seed maturity and reflected decreased permeability and the development of testa colouration. The testa precludes the use of viability stains such as nc and FDA, unless rendered permeable through scarification. This was achieved using NaOCI. Viability and germinability percentages did not correlate well for the small-seeded Disa species, indicating that i) the methods used to break dormancy are inadequate, ii) additional factors may be acting in concert with the testa to regulate germination and iii) that the determination of mature Disa seed viability is ineffective. As an alternative, the germination potential of immature seed was estimated as the ratio between the proportion of embryos stained with TTC and the proportion of seeds permeable to EVANS' blue. Attempts to relieve water-impermeable dormancy in Disa resulted in the formulation of a dual-phase protocol - with the specific aim of increasing water availability to the embryo. Dual-phase cultures comprised a solid, charcoal-rich medium overlaid with a reduced strength, liquid medium fraction of the same type. The solid fraction negated the influence of leached phenols and allowed protocorms to establish polarity, whilst the fluid fraction increased water availability. The dual-phase protocol allowed germination of nine summer-rainfall Disa species, usually in percentages that approximated their estimated germination potential. For the remaining species, germination is controlled by more complex factors. Large seeds are atypical in containing starch, the hydrolysis of which facilitated their rapid, autonomous germination. Small-seeded Disa species stored lipids and proteins and germinable species accumulated starch post-germination. The embryo protoplasts of all species contained appreciable amounts of soluble sugars, irrespective of germinability. However, decreased sucrose and increased fructose correlated significantly with decreased seed germinability. This study provides evidence of the nutritional value of mycotrophy, with endophytes liberating soluble carbohydrate and non-carbohydrate compounds upon lysis. However, few species were germinated symbiotically, suggesting that endophytes isolated from adult roots do not necessarily support germination in the same species. Similar endophytic fungi occur in Australian and Holarctic orchids.
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

In many African countries south of the Sahara, farmers depend on the cultivation of vegetatively propagated crops (VPCs) for both consumption and commercial purposes. Yet yields for these crops remain at low levels due, in part, to the persistent use of low-quality planting material. Efforts to improve the quality of planting material exchanged in markets or through other channels are often hampered by the unique biological and economic characteristics of vegetative propagation—characteristics that distinguish VPCs from the major cereal crops that drive and shape the policy and investment choices made in many of these countries. This suggests that continued investment in new technologies and systems to produce, package, and distribute VPC planting materials will require customized policies and policy support if these systems are to supply farmers with quality planting material at any significant and sustained scale. This paper explores these issues in the context of the cassava seed system in Nigeria by drawing on (1) prior research, public policy documents, and government statistics; (2) key informant interviews and focus group discussions with seed system actors; and (3) a unique dataset from the 2015 Cassava Monitoring Survey of Nigeria (CMS). The paper examines the production and supply of cassava planting material, the influence of various quality assurance systems on production and supply, and the implications for smallholder farmers in Nigeria. We describe the market, non-market, and regulatory systems that shape the cassava seed market in Nigeria, focusing on effectiveness, influence, and reach. We then explore the ground realities—how farmers actually acquire and use cassava planting material—given the (weak) state of markets and regulation. This is followed by a discussion of alternative policy and regulatory approaches to managing and expanding the cassava seed system, emphasizing a more decentralized approach that prioritizes investment in innovative capacity at the community and enterprise levels.