Dissertations / Theses on the topic 'Tomatoes – South Africa'

Thesis (M.Sc. (Crop Science)) --University of Limpopo, 2012<br>Organic tomatoes are increasingly popular with larger market acceptance since organic farming uses limited or no artificial chemicals. Application of organic fertilisers such as cattle manure has potential to boost organic tomato productivity particularly under low input farming systems. However, information is required on the optimum level of manure application on different tomato cultivars to help emerging tomato farmers in South Africa. The objective of this study was to determine the relative response of yield and yield components among selected determinate and indeterminate tomato cultivars using different levels of cattle manure. Two separate field experiments were conducted at the University of Limpopo during 2007 and 2008 using a split plot design with three replications. Two sets of tomato cultivars were included in which one set consisted indeterminate types (Money Maker, Ox Heart and Sweetie) and the other determinates (Roma and Floradade). Cultivars were assigned as the main plot treatments with six rates of manure (0, 10, 20, 30, 40 and 50 in gram per plant) applied as the subplot treatments to each set. Results indicated significant interactions (P ≤ 0.01) between indeterminate tomato cultivars and levels of manure applied for fruit yield and fruit size in both experiments. Plant height showed variation from 78 to168 cm in Experiment I and 87 to 176 cm in Experiment II. During Experiment I fruit number varied from 23 to 91 per plant and 23 to 97 in Experiment II. Significant differences were detected among determinate cultivars on fruit yield varying from 7928 to 3 4705 kg per hectare during Experiment I and 3 169 to 2 9840 kg per hectare during Experiment II. Overall, the best level of manure for maximum fruit yield and greater fruit size was achieved at 40 g per plant in the indeterminate cultivar Sweetie. Conversely, the best level of manure for maximum fruit yield was achieved at 30 g per plant in determinate cultivar Roma. Thus, to achieve maximum yield, tomato growers could apply 600 and 800 kg per hectare manure on the determinate and indeterminate tomato cultivars, respectively.<br>the National Research Foundation (NRF)

Thesis (Ph. D. (Plant Production)) -- University of Limpopo,2016<br>Refer to document<br>University of Limpopo, The Technology Innovation Agency (TIA), The Land Bank Chair of Agriculture ─ University of Limpopo, The Flemish Interuniversity Council (VLIR) and, The Agricultural Research Council - University Collaboration Centre

Effective microorganisms (EM), a commercial concoction of microbes that includes yeasts, fungi, bacteria and actinomycetes, have been found to be effective in enhancing crop growth by a number of scholars. It is registered in South Africa, but it had not been thoroughly investigated. The present study investigated the effects of EM on growth, yield and quality of tomato (Lycopersicon esculentum Mill), butternut (Curcurbita moschata) and Swiss chard (Beta vulgaris), along with selected soil properties. In field-grown tomato it was observed that the application of EM caused a significant increase in the number of fruits at seven weeks after transplanting. However, plants treated with EM alone, or EM in combination with other amendments, subsequently produced lower yields owing to an outbreak of early and late blights which affected them the most severely. Combined applications of EM with organic amendments improved plant N content and increased soil N content above initial levels. The application of compost resulted in soil N and P concentrations higher than those of the control presumably due to nutrients being slowly released from the compost material. In a follow up greenhouse trial EM application had a negative effect on tomato leaf dry matter yield, number of leaves, number of trusses, fruit yield and number of fruits. The negative effects of EM were ascribed to N immobilization by the EM that could have resulted in reduced N availability to plants. The lower number of fruits associated with EM application resulted in improved average fruit weight of tomatoes grown in the greenhouse, possibly as a result of more assimilates being partitioned to the few fruits EM application also had a negative effect on field grown butternut as reflected by lower total yield, lower marketable yield and lower first grade yield. The results were attributed to immobilization of N induced by application of EM, and to the inability of EM to control pumpkin fly that attacked very young fruit, resulting in their failure to develop or resulting in the down grading of mature fruits. The application of EM alone had a positive but non significant effect on the yields of both the first and second harvests of Swiss chard. However, when applied with compost or goat manure, a non significant negative effect on yield was observed. When applied with inorganic fertilizer, EM had no effect on yield but tended to increase the uptake of nitrogen by Swiss chard. Though goat manure had a narrower C: N ratio than compost, it did not result in greater EM effectiveness as had been hoped. However, goat manure had a more positive effect on soil properties than compost. It increased the N, P, and K contents of the soil and resulted in a narrower C: N ratio of the soil compared to compost. Generally, the results of the four trials conducted with three different crops indicated that EM had inconsistent effects on crop performance.

Since the discovery of Escherichia coli O157:H7 in the early 1980s and the increased association of foodborne outbreaks linked to fresh produce, a growing number of research articles relating to this subject have been published. Although leaps in our understanding of foodborne pathogen association with fresh produce have been made, our knowledge regarding this subject remains limited, with many research findings being contradictory. The microbial safety of commercially produced tomatoes in South Africa was investigated during 2012- 2014. Although no tomatoes tested were contaminated with either Salmonella enterica or Escherichia coli O157:H7, the presence of Salmonella enterica in the packinghouse of the first farm investigated in 2012 does indicate a potential risk associated with fresh tomatoes. Rapid, sensitive, and accurate detection of foodborne pathogens is vital to ensure produce safety. Conventional culturing techniques should be improved to reduce the analysis time, increase the efficiency of recovery, improve the resurrection and growth of injured cells, and to exclude other microorganisms present in the samples. The part of this dissertation therefore aimed to investigate the application of EnBase® technology for the enhanced recovery of sublethally injured E. coli O157:H7 from the environment and particularly surface water. Limiting fermentable carbohydrate availability through enzymatic glucose release would hypothetically prevent metabolic overload during enrichment cultivation, allowing enhanced resuscitation and growth of target organisms. This was found to be the case when E. coli O157:H7 was grown axenically under pristine conditions. EnPresso® B and variations thereof performed sub-optimally compared to buffered peptone water when used for the enrichment of E. coli O157:H7-spiked surface water in the presence of naturally occurring coliforms. The utilization of EnBase® technology for the selective and differential isolation and enumeration of sub-lethally injured E. coli O157:H7 from spiked surface water on solid media were not effective due to interference of the buffering capacity of EnPresso® B with the pH indicator neutral red. Understanding the biological and ecological factors enabling survival and persistence of human enteric bacteria in fresh produce, as well as better detection and monitoring techniques, are crucial in developing pre- and postharvest strategies to ensure safe produce in the future.<br>Dissertation (MSc)--University of Pretoria, 2015.<br>Microbiology and Plant Pathology<br>MSc<br>Unrestricted

Since the discovery of Escherichia coli O157:H7 in the early 1980s and the increased association of foodborne outbreaks linked to fresh produce, a growing number of research articles relating to this subject have been published. Although leaps in our understanding of foodborne pathogen association with fresh produce have been made, our knowledge regarding this subject remains limited, with many research findings being contradictory. The microbial safety of commercially produced tomatoes in South Africa was investigated during 2012- 2014. Although no tomatoes tested were contaminated with either Salmonella enterica or Escherichia coli O157:H7, the presence of Salmonella enterica in the packinghouse of the first farm investigated in 2012 does indicate a potential risk associated with fresh tomatoes. Rapid, sensitive, and accurate detection of foodborne pathogens is vital to ensure produce safety. Conventional culturing techniques should be improved to reduce the analysis time, increase the efficiency of recovery, improve the resurrection and growth of injured cells, and to exclude other microorganisms present in the samples. The part of this dissertation therefore aimed to investigate the application of EnBase® technology for the enhanced recovery of sublethally injured E. coli O157:H7 from the environment and particularly surface water. Limiting fermentable carbohydrate availability through enzymatic glucose release would hypothetically prevent metabolic overload during enrichment cultivation, allowing enhanced resuscitation and growth of target organisms. This was found to be the case when E. coli O157:H7 was grown axenically under pristine conditions. EnPresso® B and variations thereof performed sub-optimally compared to buffered peptone water when used for the enrichment of E. coli O157:H7-spiked surface water in the presence of naturally occurring coliforms. The utilization of EnBase® technology for the selective and differential isolation and enumeration of sub-lethally injured E. coli O157:H7 from spiked surface water on solid media were not effective due to interference of the buffering capacity of EnPresso® B with the pH indicator neutral red. Understanding the biological and ecological factors enabling survival and persistence of human enteric bacteria in fresh produce, as well as better detection and monitoring techniques, are crucial in developing pre- and postharvest strategies to ensure safe produce in the future.<br>Dissertation (MSc)--University of Pretoria, 2015.<br>Microbiology and Plant Pathology<br>MSc<br>Unrestricted

Thesis (M.Sc. Agriculture (Agricultural Economics) --University of Limpopo, 2013<br>The Limpopo Province is home to South Africa’s major tomato producer, who is also the largest producer of the commodity in the Southern Hemisphere. Regardless of its importance in the tomato industry of the country, there are few studies analysing the mechanism through which prices of tomatoes are determined and transmitted from the farm gate in Limpopo to the various provincial, local and international markets. This study attempts to fill the knowledge gap on the performance of Limpopo Province’s tomato markets by examining vertical price linkages amongst successive marketing levels. With the aid of both surveys and document analysis, daily tomato prices were collected at three levels that reflect the marketing chain of Limpopo produced tomatoes. Through marketing margin analysis, it was established that the farmers’ portion of the consumer’s Rand is low. About 85.1% of the consumer’s Rand goes to pay for marketing margins. Granger causality tests show that both the wholesale and retail prices are caused by farm gate prices, whereas an independent causal relationship was found between wholesale prices and retail prices. The study also found a long run cointegration relationship between farm gate prices and retail level prices, and not the same for the relationship between farm gate and wholesale prices. Furthermore, it was found that retailers are quick to react to increases in farm gate prices and slow in adjusting to price decreases. On the other hand, wholesale prices were found to be symmetrical to farm gate prices. These results suggest that the transmission of price information is more efficient between the farm and wholesale markets than between the farm and retail markets. Nonetheless, there is scope for increasing efficiency of tomato marketing in the province. Key words: Price transmission, marketing margins, vertical price linkage, market dominance, tomato markets, Limpopo Province

Tomato production was an important economic activity in the Limpopo Province of South Africa. A clear tomato yield gap existed between South Africa and the other countries in Southern Africa. Understanding the reasons behind tomato crop failures and successes in South Africa could increase tomato production in the fast-growing tomato markets of Angola, Mozambique and Zimbabwe, thereby improving food and nutrition security for smallholders and the population in general. In this study, the i) economics of tomato production in South Africa was investigated and compared to similar production systems in the USA, Turkey and India, ii) the interactions between biotic and abiotic factors that limited tomato yield and quality within three climatically distinct planting windows in the Limpopo Province of South Africa were examined, and iii) the correlations between three commercially available soil health metrics (i.e., a microscope-based method for estimating the biomass of soil bacteria, fungi and protozoans; nematode community profiling based on counts and trophic group classifications and related indices; polyphasic soil health testing based on soil biological, physical and chemical variables) and tomato yield were assessed. Meta-analysis was used to explore yield variation in open field production systems in the international context. The main yield-limiting factors were identified as planting times, planting density, soil-water relations, and synthetic/organic nitrogen fertilization. The focus of the study shifted to commercial tomato production in the Limpopo Province of South Africa. Since 2003, these tomato producers practiced intensive open field tomato production using a combination of synthetic and organic soil, crop and pest management technologies. A review of tomato production economics revealed that within a period of six years, South African tomato production cost per hectare more than doubled but the profit margin halved. The importance of tomato quality as an economic factor was demonstrated. Economic pressures forced these tomato producers to intensify production, which underscored the need for the continued development of sustainable tomato production systems. To achieve this strategic goal, the primary biotic and abiotic factors that limited tomato production were identified. The results indicated that complex interactions between biotic and abiotic factors explained yield and quality variation. Climate variation dominated crop productivity, especially in unsuitable planting windows. Soil and crop management variables, notably synthetic fertilizer and pesticide usage, ensured high quality yield. Soil biology management was an important aspect of sustainable agriculture and the use of appropriate soil biology metrics facilitated soil biology management at field scale. All three soil biology metrics were sensitive to distinguish between three types of disturbed soils commonly encountered in the open field tomato production context: natural, disturbed and cultivated soils. The microscope-based method used for quantifying bacterial, fungal and protozoan biomass and numbers was unsuitable for explaining yield variation. Nematode community profiling, in conjunction with polyphasic soil health testing, was very useful for explaining yield variation. In particular, soil pH, boron, aggregate stability, Paratrichodorus spp. and the balance among soil cations (especially exchangeable K and Mg) explained yield variation. In conclusion, sustainable open field tomato production depends on the integrated use of synthetic and organic crop nutrition and protection technologies, optimum planting times, disease-resistant genetic material, and cultivation on healthy soils. The findings of this study will benefit policy development in support of sustainable vegetable production in the rural areas of Southern Africa.<br>Thesis (PhD)--University of Pretoria, 2016.<br>tm2016<br>Plant Production and Soil Science<br>PhD<br>Unrestricted

Thesis (MScAgric)--Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: The availability of water for irrigation purposes is becoming a serious concern for smallholder famers in the former homeland areas of South Africa. Not only because of global weather change and the occurrence of more erratic weather events, but also due to competition for fresh water between the agricultural, industrial and domestic sectors (Hamdy et al., 2003). Food production increases in smallholder agriculture is seen as a possible solution to the food security challenges in the rural areas of the Limpopo Province (Altman et al., 2009). Smallholder farmers in Giyani mostly use traditional furrow irrigation systems and their farm crop productivity remains very low, compared to commercial farms in the same area. The objective of this study is to utilize and test various innovation technologies aimed at increasing Water Productivity (WP) in order to facilitate better irrigation management of the available water resources. The study was conducted on two farms, Zava Cooperative Garden and Mzilela Cooperative Garden, in the rural areas of Giyani over a two year period from 2012-2013. This study seeks to achieve the objective in three distinct ways. Firstly, the use of NIR technology is used to evaluate the prediction ability of soil chemical parameters for fertilizer requirement calculations. Secondly, WP trials were conducted on smallholder tomato (Solanum lycopersicum) production for three consecutive seasons, evaluating their current tomato crop production systems and also testing new innovations for WP increases. Thirdly, applying the MonQI methodology, inputs and outputs of all crop production sites were done to monitor the cropping systems throughout the period of the research. The results from this study indicate the importance of applying new innovations amongst smallholder production systems. Important findings from the NIR technologies indicated that this innovation can improve soil nutrient management in a more affordable, user friendly manner. The results showed that good prediction models were obtained for pH (KCl), electrical conductivity (EC), P, K, Mg, Na and CEC, with R2 and RPD values larger than 0.60 and 1.4 respectively. The prediction of exchangeable Ca was less successful with a R2 value of 0.43. Results from the WP trials suggest that drip irrigation performed better than furrow irrigation in terms of yield and WP. Yield and WP were very low for all treatments, being below 32 t/ha and 5.2 kg/m-3 respectively. Improved management practices, such as soil nutrient management and mulching were introduced in the 2nd and 3rd seasons of tomato trials in order to increase WP at field level at Mzilela farm. Results showed tomato yield increased from an average of 26.5 t/ha to 120.9 t/ha and WP increases from 4.61kg/m-3 to 17.69 kg/m-3. Deep drainage of water out of the rootzone decreased with better irrigation management. The results from the monitoring of inputs and output of their cropping systems revealed that smallholder farmers, using traditional farming practices, yielded very low and mostly below 5 t/ha for all crops. Some crops were totally lost due to hail and heat-waves. NPK balances for conventional cropping by the smallholder farmers at Mzilela was in the range of 0 to -70 kg/ha. The tomato production fertilized treatment of the 1st, 2nd and 3rd WP trials, showed positive nutrient balance results for P and K in the range of 80 to 140 kg/ha. N balances were mostly negative for all plots. NFI was R2768 and R4740 for season 1 and 3 respectively, while the 2nd season results showed a loss of - R5176. With the improved yield from the WP trial sites, and the fruits being sold to the Spar, the NFI increased to R42486 in the final season. The study concludes that great improvements in yield, WP and NFI are attainable and sustainable amongst smallholder farmers in the Giyani area.<br>AFRIKAANSE OPSOMMING: Die beskikbaarheid van water hulpbronne vir besproeiings doeleindes onder kleinskaalse boere in die voormalige tuislande is besig om ernstige bekommernisse te wek. Nie net as gevolg van globale weer veranderinge en meer gereelde ekstreme weer toestande nie, maar ook as gevolg van die kompetisie tussen die landbou, industriële en huishoudelike sektore vir water gebruike (Hamdy et al., 2003). Verhoogde voedsel produksie onder die kleinskaalse landbou sektor word gesien as moontlike oplossing vir die voedsel sekuriteit uitdagings in die platteland areas van die Limpopo Provinsie in Suid-Afrika (Altman et al., 2009). Kleinskaalse boere in Giyani gebruik meestal tradisionele voor-besproeiings stelsels en hul produktiwiteit bly steeds baie laag wanneer dit met kommersiële boerderye vergelyk word. Die hoofdoel van hierdie studie is om Water Produktiwiteit (WP) te bestudeer en verskeie innovasie tegnologieë te toets om beter besproeiing bestuur van kosbare water bronne te fasiliteer. Die studie was uitgevoer op twee plase, naamlik Zava Koöperatiewe Tuin en Mzilela Koöperatiewe Tuin, wat in die plattelandse areas van Giyani geleë is en die studie is gedoen oor ‘n periode van twee jaar vanaf 2012 tot 2013. Om hierdie doelwit te bereik was die navorsing in drie eenhede uitgevoer. Eerstens sal Naby-Infra Rooi (NIR) tegnologie gebruik word om die voorspelling vermoë van grond chemiese eienskappe te toets vir meer effektiewe grond voedingstof bestuur deur kleinboere. Tweedens sal WP proewe uitgevoer word op kleinskaalse tamatie (Solanum lycopersicum) produksie. Die huidige tamatie gewasproduksie stelsels was getoets om die WP statusse te evalueer van hul tradisionele bestuurs praktyke van beide drip- en voorbesproeiings stelsels. Laastens, is insette en uitsette van die kleinboere se produksie stelsels met die MonQI metodologie bestudeer om die huidige produksie sisteme te evalueer, sowel as die WP proef persele, deur opbrengs, grond voedingstof balanse en netto plaas inkomste (NPI) te moniteer en te bereken vir 4 half jaar seisoene gedurende die navorsings periode. Die resultate van die navorsing voer aan dat die gebruik van innovasie tegnologieë onder kleinskaalse boerderystelsels ontsettend belangrik is vir verbeterde produksie. Hoofbevindings van die NIR tegnologie dui dat meer doeltreffende grond voedingstof bestuur moontlik is en wat goedkoper en meer gebruikersvriendelik is vir kleinboere. Hierdie tegniek het goeie voorspelbaarheid-modelle getoon vir pH (KCl), Elektriese Geleiding (EG), P, K, Mg, Na en katioon uitruilings kapasiteit (KUK) met R2 en RPD waardes hoër as 0.60 en 1.4 onderskeidelik. Die voorspelbaarheid van Ca was minder suksesvol met ‘n R2 waarde van 0.43. Die resultate van die WP toetse wys dat drip besproeiing beter as voorbesproeiing presteer het in terme van opbrengs en WP. Opbrengs en WP was baie laag vir alle behandelings van seisoen 1, met waardes laer as 32 t/ha en 5.2 kg/m-3 onderskeidelik. Verbeterde bestuurspraktyke, soos grond voedingstof bestuur asook die gebruik van ‘n deklaag, was in die 2de en 3rde seisoen toegepas om opbrengs en WP te verhoog op plaasskaal op Mziela plaas. Resultate het gewys dat opbrengs verhoog het van ‘n gemiddelde van 26.5 t/ha tot 120.9 t/ha en WP verhoging van 4.61 kg/m-3 tot 17.69 kg/m-3. In terme van die insette en uitsette van die produksie sisteme het opbrengste van alle gewasse, wat nog van tradisionele metodes gebruik, laer as 5 t/ha getoon. Soms van die totale oeste verloor deur hael of hittegolwe. Die NPK balanse vir die gewasverbouing met konvensionele kleinboer metodes was in die orde van 0 tot -70 kg/ha. Die kunsmis behandelings van die tamatie proewe van die 1ste, 2de en 3rde WP seisoene het positiewe balanse getoon vir P en K in die orde van 80 tot 140 kg/ha. Die N balanse was meestal negatief vir alle verbouings persele. Die NPI was R2768 en R4740 vir seisoen 1 en 3 onderskeidelik, terwyl die 2de seisoen verlies van -R5176 getoon het. Die verbeteringe in opbrengs met die WP proewe en met die verkoop van die tamaties aan die Spar was die NPI vir die 4de seisoen R42486. Die studie sluit dat daar groot moontlikehede is vir verhoging in opbrengs, WP en NPI onder kleinboere in die Giyani area.

Student Number : 0314429G - MSc research report - School of Molecular and Cell Biology - Faculty of Science<br>Tomato (Lycopersicon esculentum) is a horticultural commodity of great economic importance in many parts of the world, including South Africa. A previous study identified a new begomovirus, Tomato curly stunt virus (ToCSV), as the causative virus of a new and potentially devastating disease of tomatoes in South Africa. In this study, symptomatic plants, suspected of infection with an uncharacterized ToCSV isolate (01/2521) were collected for screening from Pietermaritzburg, South Africa. A host range study was conducted with the original ToCSV isolate (99/0631). Two small DNA molecules (1449 nts and 755 nts) were found associated with ToCSV [01/2521] using near-full length primers AL1c2745 and PAR1v32 specific for ToCSV. A single small DNA molecule (842 nts) was also found in association with the original ToCSV isolate. Nucleotide sequence analysis revealed that the two small DNA molecules (1449bp and 755bp) have no significant nucleotide sequence identity (less than 20%) with any known begomovirus. The 842bp molecule has the most significant nucleotide sequence identity (48%) to that of ToCSV (AF261885), while less than 20% nucleotide sequence identities were found when compared with other begomoviruses. Nucleotide sequence alignment of the 842bp DNA molecule to the ToCSV sequence, showed that this small DNA molecule is a chimeric molecule that could have arisen through recombination, partly from the coding regions of the ToCSV genome, but the rest of the molecule is of unknown origin. All three small DNA molecules identified in this study were compared to some known begomovirus associated subgenomic molecules and satellite molecules, and sequence identities of less than 20% were found. To our knowledge, this is the first report of a small DNA molecule found associated with the ToCSV genome. The complete genome sequence of ToCSV [01/2521] was not determined. Based on the results we obtained from the host range study, all the chosen test plants are not susceptible to ToCSV infection. The infectivity of all the small molecules identified in this study, is currently being investigated.

MSCAGR (Agricultural Economics)<br>Department of Agricultural Economics and Agribusiness<br>study aimed to determine factors that influenced the price of tomatoes sold by hawkers on the roadside market. The study also aimed at determining whether any socio-economic characteristics of hawkers who sold tomatoes had significant impact on the price paid my consumers. The study was conducted in the Thulamela local municipality under Vhembe District of Limpopo, South Africa. A stratified random sampling technique was used to select participants for this study. A sample size of 198 hawkers were drawn randomly. Structured questionnaires were administered through face-to-face interview. Descriptive statistics, correlation matrix, multiple linear hedonic regression and stepwise linear regression were used to analyse collected data. With regards socio-economic characteristics, only age was found to have significant impact on the market price received by hawkers. Smooth appearance, rough appearance, round shape, oval shape, and red and yellow colour tomatoes had a significant impact on the average market price. It is therefore recommended that attribute such appearances, colour, shapes and sizes of tomatoes should be considered when selling tomatoes at both retail and farm level. This will result in more purchase of tomatoes that will eventually contribute to increase in household income and reduction in poverty.

M.Sc.<br>Loss of quality occurs when tomatoes are stored for more than approximately 3-5 weeks at 12 °C. The most common disorders found in tomatoes during storage are colour development to an unacceptable shade of red, softening, shrivelling due to moisture loss, loss of flavour and fungal infections. Storage life of tomatoes is generally extended by storage under refrigeration. Further, extension of shelf life can be achieved by modified atmosphere packaging (MAP). This is done by sealing actively respiring produce in polymeric film packages to modify the 0, and CO, levels within the package atmosphere. Also, 1-methylcyclopropene (1-MCP) has been proven to be an effective postharvest treatment to prolong the storage life of tomatoes. In the present study four trails were conducted. In the first trial the effects of 1-MCP dosage rate and the colour stage of harvest on the quality of `Santa' tomatoes stored for 4 weeks at 12 °C were investigated. The results indicated that ripening related changes were delayed following 1-MCP treatment. 1-MCP treated fruit were firmer, had reduced TA losses, slower colour development, and reduced physiological disorders associated with long term storage. The stage of ripeness influenced the efficacy of 1-MCP on slowing down the tomato ripening process. 1-MCP was of little benefit for fruit treated at stage 4 of ripeness. In contrast, particularly when the 1-MCP dosage was high, 1-MCP markedly delayed ripening in fruit harvested at colour stage 2 and 3, but the quality attributes such as SSC were better in treated fruits harvested at stage 3. Relatively little difference was observed between 250 and 500 nL.L -I 1-MCP and thus 500 nL.Con fruit harvested at stage 3 of ripeness was used in the remaining experiments. Effects of MAP, 1-MCP and imazalil either as combined treatments or as single treatments were studied for their effect on the quality of tomatoes. Ripening related changes were delayed and loss of weight was significantly reduced following 1-MCP treatment and MA packaging in 17 gm thickness bags. Elevated CO, in MAP after a long storage period induced anaerobic metabolism with the generation of off-odurs and the proliferation of anaerobic microbes. Selected doses of imazalil (0, 0.5, 0.05, 0.005 and 0.0005 g.L.1 ) were evaluated for their effect on the fungal infections on tomato fruits. Imazalil at a rate of 0.005 g.L"' was found to reduce fungal infections by 50% when used in combination with MAP and 1-MCP. The combination of imazalil and MAP therefore appears to be the best treatment combination to facilitate export of 'Santa' tomatoes by sea. However, with regards to reducing the loss of TA, treatment with 1-MCP would be beneficial.

Submitted in fulfilment of the requirements for the degree of Master of Applied Science in Food Science and Technology, Durban University of Technology, 2015.<br>Listeria monocytogenes have been implicated as a public health concern worldwide. The study explored the survival of non-adapted, heat adapted and chlorine adapted L. monocytogenes on tomatoes; as well as the survival of non-adapted, heat adapted and chlorine adapted biofilms after exposure to sodium dodecyl sulphate (SDS), levulinc acid, sodium hypochlorite solution. Contact time of 1, 3 and 5 minutes was used. The survival of L. monocytogenes was monitored at 0, 24, 48 and 72 hours. The sanitizers were used individually or combined as follows; 1% sodium dodecyl sulphate individually; 0.5% levulinic acid individually; 200 ppm sodium hypochlorite solution individually and 0.5% levulinic acid/0.05% sodium dodecyl sulphate in combination (mixture). The samples were kept at 4 °C throughout the period of assessment. The effect of these sanitizers on pH, total soluble solids (TSS) and titratable acidity (TA) was also determined. Furthermore, the attachment of L. monocytogenes on tomatoes was investigated using a scanning electron microscope. Highest log reduction of non-adapted L. monocytogenes were observed on tomatoes treated with 1% SDS and least log reduction was achieved when tomatoes were treated with sodium hypochlorite solution. Though the log reduction achieved by 0.5% levulinic acid was higher that sodium hypochlorite solution, it was lower than log reduction achieved when 0.05% SDS / 0.5% levulinic acid mixture was used for all contact times. Using non-adapted L. monocytogenes, SDS was able to destroy all L. monocytogenes at 1, 3 and 5 minutes contact time. The trend was the same when heat adapted and chlorine adapted L. monocytogenes were used. There was no significant log reduction observed with biofilms. More favourable results were observed as contact time was increased from 1 to 5 minutes. Though there was a decrease in surviving bacteria from 1 to 3 minutes contact time, this decrease was not significant. The study investigated if exposure to sanitizer has an effect on pH, titratable acidity (TA) and total soluble solids (TSS) of the tomatoes. It was revealed that levulinic acid and mixture can have detrimental effect on pH, TA and TSS of tomatoes. The TA and TSS of samples treated with levulinic acid and mixture varied significantly (P ≤ 0.05) compared to the control sample. Although the TA and TSS of samples treated with SDS and sodium hypochlorite solution were different from the control, the differences were not significant. As much as sanitizers have the potential to reduce the bacterial population in fresh produce they may not completely destroy pathogens. Chlorine based sanitizers such as sodium hypochlorite though frequently used in the fresh produce industry, are not the best sanitizer to be used against food borne pathogens. Other sanitizers such as SDS used alone or in combination with another sanitizer can achieve better results than the widely used sodium hypochlorite solution as observed in this study. Stress adapted pathogens become less responsive to sanitizers during subsequent treatments. Through this research, it was established that biofilms are resistant to sanitizers. Though application of sanitizers in fresh produce is cheaper and simpler to apply, there is need to monitor varying concentrations of sanitizers, contact time and minimise contact with sub-surfaces as this could lead to sensory quality losses.

M. Tech. Agriculture<br>Tomatoes (Solanum lycopersicum) and sweet or bell peppers (Capsicum annuum L.) belong to the Solanaceae family. They constitute an excellent source of phenolic (flavonoids), vitamin C (ascorbic acid) and carotenoids (especially lycopene, b- carotene, a precursor of vitamin A), known as antioxidants. The aim of this study was to investigate the influence of photo-selective nets (ChromatiNet™) (red, pearl and yellow) with 40% shading on postharvest fruit quality parameters (Soluble solids content, Titratable acidity, fruit mass and firmness), bioactive compounds (ascorbic acid, total phenols, flavonoid, lycopene, b-carotene contents), antioxidant scavenging activity, odour active aroma compounds and the sensory quality of three indeterminate sweet pepper cultivars HTSP-5 (green), HTSP-3 (red) and Celaya (yellow) and three tomato cultivars (AlfaV, Irit, and SCX 248). A commercial black net (control) with 25% shading was included for comparison.

The use of pheromone-based or semiochemical lures and devices for the detection of insect pest population and monitoring in agriculture is a common practice. In many countries the use of these devices is exempt from registration requirements based on regulatory thresholds set by the relevant authorities, however, not in South Africa. The question arises whether the pheromones or semiochemicals dispensed through such devices, influence the naturally occurring compounds observed and whether a concern of toxicity and ecotoxicity is justified. A tomato field was selected in a commercial growing area of South Africa and a novel five-component lure, T.V. PheroLure®, was identified from a local manufacturer, Insect Science (Pty) Ltd. The T.V. PheroLure® consists of a Volatile Organic Compound (VOC) blend which is placed in a polyethylene bulb. Tomato VOCs were collected before, during and after the application of the T.V. PheroLure® which was used in combination with a yellow bucket funnel trap. The VOCs were collected at different heights (0 cm, 30 cm and 60 cm) of the tomato plants, from planting until harvest (22 weeks) and surrounding tomato fields without the T.V. PheroLure®. The results obtained indicated that: (i) the T.V. PheroLure® had no significant influence on the natural VOCs observed in the tomato field and (ii) that the height of sampling had no influence on VOCs observed. This study also indicated that apart from a slight increased contribution of limonene, there was no significant influence observed from the T.V. PheroLure® compounds on the natural background VOCs found in the tomato field. Therefore, it could be argued that the natural phenology of the plant has a greater influence on the VOCs observed than T.V. PheroLure® and that the concern of toxicity and ecotoxicity is unjustified when using these devices for monitoring purposes only.<br>Environmental Sciences<br>M. Sc. (Environmental Science)

The tomato is one of the most important vegetable crops grown in the South African community. Most hydroponic tomato growers in South Africa are using sawdust as a growing medium due to its availability and affordability. However, there is little or no information on how particle sizes of sawdust influence tomato yield and quality. The aim of the study was to determine the effect of the particle size of sawdust on plant growth, yield and quality of tomato. Six treatments of different particle sizes of sawdust i.e. fine (F), medium (M), coarse (C) and 50:50 ratio of F: M, C: M, and C: F extracted from pine tree were used for the experiment. Treatments were arranged in a randomized complete block design with four replicates. The size of the sawdust particles did not have a significant effect on plant height, stem diameter, leaf length and width, shelf-life, marketable yield, total yield and unmarketable yield. A tendency to increase marketable and total yield was observed when tomato plants were grown at a 50:50 C: F ratio. Fruit and leaf mineral content were not affected by sawdust particle size. After completion of the experiment, air- filled porosity was significantly high on particle size C, M, and C: M while the water holding capacity was significantly high on F followed by M. The study showed that the suitable growth medium for production of tomatoes under the hydroponics system used was the CF particle substrate. Generally, the experimental crop performed better under the CF particle substrate in terms of growth parameters, and fruit quality, thus leading to the conclusion that the CF growth medium is ideal for hydroponically grown tomato under a non-environmentally controlled polytunne<br>Agriculture, Animal Health and Human Ecology<br>M. Sc. (Agriculture)

M. Tech. Agriculture.<br>Investigates the effect of photo-selective nets on plant growth parameters (plant height, leaf area, leaf chlorophyll, stem diameter, flowering intensity, and fruit settings), pest and disease incidence, and yield (number of fruits per plant) in three selected cultivars.Secondly, to investigate the effect of shading on fruit quality parameters (fruit mass, firmness, colour, soluble solids content, and titratable acidity) and health promoting compounds (ascorbic acid, lycopene content, β-carotene, total phenols and flavonoids, and antioxidant scavenging activity) in three selected tomato cultivars.

Tomato spotted wilt virus (TSWV), a Tospovirus, is one of the ten most economically destructive plant viruses worldwide, causing losses exceeding one billion U.S. dollars annually on several crops. In South Africa (SA), TSWV has become an important virus in many economically important crops. The main objective of this research project was to isolate, identify and characterise TSWV isolates occurring in SA. A review of current literature assembled background information on TSWV molecular biology, epidemiology, transmission, detection and control. A TSWV isolate infecting pepper (Capsicum sp.) occurring in KZN was isolated and partially characterised. The virus was positively identified as TSWV using the enzyme-linked immunosorbent assay (ELISA) and the presence of typical necrotic TSWV symptoms on Nicotinia rustica L. Symptomatic leaves were harvested and the virus was partially purified using standard procedures. Under the transmission electron microscope (TEM), typical quasi-spherical and dumbbell-shaped particles of 80-100nm in diameter were observed in negatively stained preparations of both crude and purified virus samples. In negatively stained ultra-thin virus infected leaf sections, an abundance of mature viral particles (100nm) housed in the cisternae of the endoplasmic reticulum (ER) were observed among typical viroplasm inclusions (30nm) and hollow tubules (200-300nm). A viral protein migrating as a 29kDa band, which corresponds to the TSWV nucleocapsid (N) protein, was observed after sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Total plant RNA, isolated from N. rustica displaying typical symptoms was subjected to reverse-transcription polymerase chain reaction (RT-PCR) using .primers specific to the nucleocapsid (N) gene. An expected 760bp product was amplified. The results obtained in this study confirm the presence of TSWV in infected pepper plants from KZN. The genetic diversity of TSWV isolates occurring in SA was examined. The nucleocapsid (N) gene sequences of six SA TSWV isolates originating from Gauteng, KwaZulu-Natal, North West, Limpopo and Mpumulanga provinces were determined and used in a phylogenetic tree comparison with TSWV isolates occurring in different geographical locations in the world. Nucleotide sequence comparisons of the N gene revealed high levels of similarity between the SA isolates and TSWV isolates from Asia and Europe. SA isolates showed a high degree of sequence similarity (99-100%) which was reflected in their distinct clustering pattern. The resistance of tomato (Lycopersicon escuJentum Mill.) plants with natural and transgenic resistance against mechanical inoculation with TSWV isolates occurring in SA was evaluated. The Stevens cultivar which has natural resistance conferred by the Sw-5 gene and the transgenic 13-1 line, which expresses the nucleocapsid (N) protein gene of the TSWV-BL isolate, was used as test cultivars. Plants were assessed for TSWV resistance using a disease severity rating scale and measurements of virion accumulation levels (A405nm). There were no significant differences among the reactions produced by the six TSWV isolates on the test plants. Although both plants were susceptible to the SA TSWV isolates by exhibiting similarly high viral accumulation levels, the transgenic tomato line showed milder disease severity compared to the natural resistant cultivar. Results suggest that transgenic resistance is a more effective approach in the control of TSWV in SA. The information generated in this study will be useful in formulating effective control measures using genetic engineering approaches for this economically important virus. Such approaches will be used as a tool to make strategic decisions in an integrated control programme for ISWV.<br>Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

PhD<br>In South Africa, tomato (Solanum /ycopersicum) is an important vegetable crop with considerable nutritional and economic value. Over the last decade, begomovirus (family Geminiviridae) infections associated with an upsurge of the whitefly vector, Bemisia tabaci, on tomato crops has become a serious threat to sustainable tomato production in South Africa. Begomovirus disease control in tomato is challenging and requires an integrated "pest" and "vector" management strategy, primarily based on the use of chemical and cultural practices aimed at reducing the virus vector as well as the use of resistant cultivars. Development of effective disease management practices for South Africa therefore requires detailed information on the complex vector-virus-host cropping system interactions. The aim of the study presented in this thesis was to investigate the South African whitefly vector/begomovirus/tomato-host pathosystem, with emphasis on the virus and vector diversity and distribution, and the identification of possible resistance sources. A survey of tomato-infecting begomoviruses was conducted during a six-year period (2006-2011 ). Techniques used to determine begomoviruses diversity included whole genome amplification using PCR, RCA (rolling circle amplification), conventional as well as next generation sequencing and development of a RCA-RFLP (restriction fragment length polymorphism) for rapid assessment of diversity. Sequence comparisons and phylogenetic analyses revealed the presence of three new monopartite begomovirus species, in addition to ToCSV, all of which belong to the African/South West Indian Ocean (SWIO) begomovirus clade. Recombination analysis indicated that all four tomato-infecting begomovirus species appear to be complex recombinants and suggests that they have evolved within the sub-Saharan Africa region, along with other African begomoviruses and that they are most likely indigenous to the region. Several weed species were also confirmed as symptomless begomovirus reservoirs, supporting their role in the emerging begomovirus epidemics in South Africa.

The Limpopo Province is a major tomato growing region in South Africa, producing 66% of the total annual tonnage of tomatoes. The Limpopo Province is particularly vulnerable to the impact of climate change, partly because it is exposed to extreme weather events. According to the Intergovernmental Panel on Climate Change (IPCC) Africa will be hit hardest by climate change as larger areas could be stricken by yield decreases of over 50% by the year 2020 because of an increasingly hotter and drier climate. This will threaten food security and the livelihoods of people in most parts of Africa. First and foremost in this research study, a detailed analysis of annual seasonal trends in minimum and maximum temperatures was investigated, as well as the diurnal temperature range over the Limpopo Province for the period 1950-1999. In particular, using daily data from 30 catchment areas, three temperature variables were calculated: the average, maximum and minimum temperature. The analysis demonstrated that there was an increase of 0.12°C every decade in the mean annual temperature for the 30 catchments over the 50-year period. Furthermore, the present study analysed the correlation of tomato records for the Limpopo Province with climatic variables in order to assess the climate change effects on tomato production and food security in South Africa. The trend analysis of tomato production in the Limpopo, tomato yield showed increased by a factor of 2 from 1971-2006. Thus the response of tomato production during that period of 35 years was more favourable. This shows that the largest values in tomato yield were in the last decades when temperatures were high. From our analysis, the trend of tomato production in the Limpopo, tomato yield increased by a factor of 2 during the period of 1971-2006 was not significant. In particular, during the spring, summer, autumn and winter seasons, tomato yield increased by a factor of 2 respectively. With the exception of February and June, most months registered positive trends in tomato production. The study reported in this thesis investigated the frequency of occurrence of heat waves (HWs) over Limpopo. The analysis of the occurrences of HWs over this region is important due to their impact on agricultural production as well as human health. Overall, our results indicate that during the period 1950-1999, the Limpopo Province experienced HW events. The results from the present study demonstrated that during the four seasons (spring, summer, autumn and winter) the HW trends were not monotonic over the five decades (1950-1999). Furthermore, the research reported in this thesis analysed the distribution of leafminer agromyzid pest over the Limpopo Province in a changing climate. The analysis of tomato pest distribution is vital because the leafminer agromyzid pest has a major impact on tomato production. In general, the aim of analysing the leafminer agromyzid pest was to determine how climate change influences the distribution of the leafminer agromyzid pest and hence impacts on tomato production in the Limpopo Province, South Africa. The present analysis illustrates that the leafminer agromyzid pest and climatic factors exhibit a non-linear relationship, which could be best described by a polynomial function of order two while in general, the influence of climate change on the spatial distribution of the leafminer agromyzid pest over the Limpopo Province is apparent.<br>Thesis (PhD)--University of Pretoria, 2014.<br>lk2014<br>Zoology and Entomology<br>PhD<br>Unrestricted