Masters Degrees (Plant Pathology)

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Browsing Masters Degrees (Plant Pathology) by browse.metadata.advisor "Flett, B. C."

Now showing 1 - 5 of 5
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    Evaluation of maize breeding populations for resistance to Fusarium verticillioides and fumonisin contamination
    (Stellenbosch : Stellenbosch University, 2017-03) Netshifhefhe, Nakisani Elelwani Innocentia; Rose, Lindy J. ; Viljoen, Altus; Flett, B. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH SUMMARY: Maize is an important crop cultivated all around the world. It is the main source of carbohydrates for over 200 million people in Sub-Saharan Africa. Daily consumption rates can reach up to 500 g per person in certain regions of Africa. Maize production is threatened by several abiotic and biotic factors which include fungi that cause maize ear rots. Fusarium verticillioides, which causes Fusarium ear rot (FER), and Aspergillus flavus, which causes Aspergillus ear rot (AER), are the most common fungal species associated with maize produced in southern and eastern Africa, respectively. Moreover, F. verticillioides produces fumonisins and A. flavus produces aflatoxins which are toxic secondary metabolites associated with harmful effects on humans and animals. Although several management strategies can be used to reduce mycotoxin accumulation in grain, host resistance has been documented to be the most efficient, cost-effective and environmentally sound strategy to minimize contamination. This study focused on evaluating F1 hybrids for improved resistance to FER and fumonisin contamination under South African and Kenyan conditions. A number of hybrids exhibited improved resistance to FER, fungal and fumonisin contamination. In South Africa, hybrids R119W x CKL05015, CML495 x CKL05015 and CKL05015 x R119W were the most resistant to FER severity, F. verticillioides colonisation and fumonisin contamination, respectively. Under Kenyan conditions, fungal colonisation was lowest in hybrids CKL05015 x CML495 and MIRTC5 x CML495, while fumonisin concentrations were lowest in hybrids CML444 x MIRTC5 and R119W x CKL05015. Parental inbred line performance was indicative of F1 hybrids performance. CIMMYT inbred lines CKL05015 and CML495, previously characterised as resistant to AER, exhibited significant resistance to F. verticillioides and its fumonisins across both countries. These lines were also found to be good general combiners for resistance to fumonisin contamination. Furthermore, F2 populations were also evaluated and the resistant F2 populations identified in this study can be used to produce recombinant inbred lines to utilise in genetic fingerprinting and mapping of resistant genes. Significant genotype x environment interactions influenced FER severity, fungal and fumonisin accumulation in maize grain. General combining ability (GCA) and specific combining ability (SCA) were significant for all three infection parameters evaluated while additive gene effects were predominant in the inheritance of resistance in this set of hybrids. This study provided fundamental information on maize lines that could be used by breeders to develop resistant cultivars. Based on the findings of this study, breeding for resistance to F. verticillioides and its fumonisins should be successful and expedited if the parental material involved is resistant.
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    Monitoring fusarium, gibberella and diplodia ear rots and associated mycotoxins in maize grown under different cropping systems
    (Stellenbosch : Stellenbosch University, 2017-03) Mabuza, Londiwe; Rose, Lindy J. ; Janse van Rensburg, B.; Flett, B. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH SUMMARY: Maize ear rots represent a significant problem in most maize production areas resulting in reduced yield and quality due to visible fungal infection and mycotoxin contamination of maize grain. Mycotoxigenic fungi affecting cereal grains are particularly important for humans and animals as they pose food safety and security concerns. Increased maize productivity relies on integrated management strategies which include limiting soil erosion and water runoff. Therefore, agricultural practices that involve no-till and the retention of previous crop residues and/or cover crops are steadily increasing in maize production areas in South Africa. The relationship between no-till, the presence of crop residue in the field and maize ear rot disease severity and mycotoxin contamination is not well understood. The increase in the use of cropping systems that support the retention of crop residues in the field could have substantial impacts on maize production and food safety in South Africa. Adequate understanding of the role of agricultural practices in disease outbreaks can assist in enhancing management of maize ear rot pathogens. In this study, the influence of different cropping systems on F. verticillioides and F. graminearum accumulation, Diplodia ear rot (DER) incidence as well as mycotoxin contamination in maize grain was determined. Cropping systems did not significantly affect F. verticillioides accumulation, zearalenone and nivalenol contamination in all the years of evaluation. Fusarium graminearum accumulation, DER incidence and deoxynivalenol contamination were, however, significantly affected in certain years when disease development was favoured. A survey to establish the effect of no-till and conventional tillage practices on Fusarium ear rot, Gibberella ear rot and DER in maize grain and resultant mycotoxin contamination in maize grain was also conducted in commercial farms in South Africa. Additionally, the survival of F. graminearum and F. verticillioides as well fumonisin contamination in crop residue samples collected from conservation and conventional tillage commercial farms in South Africa was also investigated. Tillage practices did not have an effect of fungal accumulation, disease incidence and mycotoxin contamination in maize grain. The results from this study indicate that under local conditions, conservational agricultural practices can be used without the potential risk of enhanced disease accumulation and mycotoxin contamination. Fusarium graminearum and F. verticillioides accumulation and traces of fumonisins were quantified from all analysed crop residues and did not differ between tillage practices. The recovery of these ear rot-causing fungi from crop residues is an indication of its potential to act as inoculum reservoirs for these fungi. Although the levels of fungal target DNA quantified from the crop residues was low, the fungi may reproduce, survive and infect subsequent hosts.
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    Mycotoxin contamination of maize and groundnut produced by subsistence farmers in northern KwaZulu-Natal
    (Stellenbosch : Stellenbosch University, 2018-03) Phokane, Sylvia; Rose, Lindy J. ; Flett, B. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Subsistence farmers in South Africa face many production challenges including infection of their grain crops with mycotoxigenic fungi and concomitant mycotoxin contamination. Fusarium spp. and Aspergillus spp. are the most common fungal species infecting maize and groundnuts while plant-parasitic nematodes are also associated with groundnuts in South Africa. Maize and groundnut questionnaires regarding production practices were presented to subsistence farmers in Pongola, Vryheid, Jozini, Manguzi and Mbazwana districts of northern KwaZulu-Natal (KZN), South Africa. Maize and groundnut grain samples were also collected at harvest and after three months of storage during the 2012/13 and 2013/14 seasons. Groundnuts, roots and soil samples were collected before harvest during the 2013/14 season, only. Fusarium graminearum, F. verticillioides and A. flavus target DNA levels were quantified in maize using quantitative polymerase chain reaction and the presence of multi-mycotoxins were determined using the liquid chromatography tandem mass spectrometry. Nematodes were extracted using sieving method and identified microscopically. Questionnaires revealed that over 90% of farmers were not aware of mycotoxins or their implications on human and livestock health. Visually diseased grain was often fed to livestock sensitive to mycotoxicosis such as chickens. Production practices amongst some farmers including crop rotation and the well-ventilated storage of grain may contribute to reduced mycotoxin contamination. In maize grain the Fusarium graminearum levels were significantly higher than F. verticillioides and A. flavus levels in both seasons. Contrary to expectations, zearalenone, produced by F. graminearum, was very low (<0.02 μg/g) at harvest and storage during both seasons while deoxynivalenol and nivalenol was not detected. There were significant differences between districts (localities) and collection periods (harvest and storage) and localities per seasons (P < 0.05) for all mycotoxigenic fungi and mycotoxins evaluated. Maize sampled in Jozini district was the most contaminated with mycotoxigenic fungi and mycotoxins while Mbazwana and Manguzi districts were the least contaminated. Four plant-parasitic nematodes, namely D. africanus, Pratylenchus spp., Meloidogyne spp. and Helicotylenchus spp., were identified from groundnut samples obtained in Jozini, Manguzi and Mbazwana during the 2012/13 and 2013/14 seasons. Furthermore, Tylenchus spp. was identified for the first time in groundnuts, pegs and soil collected before harvest during the 2013/14 season. Results from this study showed that there is a need for mycotoxin awareness campaigns and additional surveillance to continuously monitor mycotoxin contamination and potential exposure. More in-depth analyses of all the potential factors contributing to mycotoxin contamination and exposure, particularly in the subsistence production are of northern KZN, is warranted.
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    Mycotoxin levels in subsistence farming systems in South Africa
    (Stellenbosch : Stellenbosch University, 2008-03) Ncube, Edson; Waalwijk, C.; Flett, B. C.; Viljoen, Altus; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Fusarium spp. and Aspergillus spp. are toxin-producing fungi associated with maize and groundnut. Fusarium verticillioides produces fumonisins in maize, and Aspergillus flavus produces aflatoxins in maize and groundnut kernels. Both toxins are responsible for carcinogenesis in humans and animals. Contamination of maize and groundnut with mycotoxins is often most severe in rural areas where subsistence farmers are unaware of their existence and follow agricultural practices that might contribute to their production. A questionnaire was, therefore, compiled to investigate agricultural decisions in rural areas that may influence mycotoxin contamination of crops. During 2006 and 2007, maize and groundnut samples were collected in the Eastern Cape, KwaZulu-Natal (KZN), Limpopo, and Mpumalanga provinces. Mycotoxin levels were quantified using the ELISA technique, and the incidence of Fusarium spp. in maize grain was determined by plating maize kernels out on Fusarium selective medium. Fumonisin-producing Fusarium spp. were also quantified using real-time PCR (TaqMan). The incidence of A. flavus and A. parasiticus in groundnut was determined by plating out kernels on potato dextrose agar. Fumonisin contamination levels in maize samples ranged from 0-21.8 parts per million (ppm) and aflatoxin levels ranged from 0- 49 parts per billion (ppb), depending on the region where samples were collected. Aflatoxin levels in groundnut ranged from 0-160.1 ppb. Fusarium verticillioides was the most common Fusarium sp. in maize followed by F. subglutinans and F. proliferatum, respectively. Regression analyses showed a positive correlation between fumonisin-producing Fusarium species when determined by real-time PCR and fumonisin concentration (r2=0.866). Regression analyses further showed a highly significant positive correlation between A. flavus and aflatoxin contamination (r2=0.10235). Samples from northern KZN contained levels of mycotoxins that were far in excess of the maximum levels set by the Food and Drug Administration in the USA. In South Africa there are currently no regulations with regard to the maximum allowable levels of fumonisin in human food. The high incidence of mycotoxin contamination of human food in subsistence farming systems indicates the need for awareness programmes and further research.
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    Resistance in South African maize inbred lines to the major ear rot diseases and associated mycotoxin contamination
    (Stellenbosch : Stellenbosch University, 2014-12) Mouton, Marili; Viljoen, Altus; Rose, Lindy J. ; Flett, B. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Maize (Zea mays L.) is one of the most important grain crops produced globally and serves as the primary source of carbohydrates and vitamins to millions of people in Africa. Whenever environmental conditions are favourable, fungal species such as Fusarium verticillioides, Fusarium graminearum sensu lato, Aspergillus flavus and Stenocarpella maydis frequently infect the ears of maize, reducing yield and grain quality. Of greater economic concern is the contamination of maize kernels with mycotoxins produced by ear rot pathogens due to its association with mycotoxicoses and immune suppression in humans and animals. Outbreaks of ear rot diseases commence in the field, but their associated toxins can be produced along the value chain. Planting resistant cultivars, as part of an integrated management strategy, could provide effective means of controlling preharvest ear rot diseases and mycotoxin accumulation in maize. Maize cultivars resistant to the major ear rot fungi and their mycotoxins are not yet available in South Africa and therefore should be developed in plant improvement programmes where durable resistance is combined with useful agronomic traits. The first step in introducing resistance into maize cultivars would be to find sources of genetic resistance. Infertility or unwanted traits may be present in wild relatives or other species of maize, and therefore locally adapted breeding material would be the most desirable source. This research aimed to identify publically available maize genotypes with durable resistance to the major ear rot pathogens and their associated mycotoxins in South Africa. In this study, a collection of inbred lines with diverse genetic backgrounds and valuable agronomic characteristics were evaluated under a range of field conditions. Some inbred lines were resistant to Fusarium ear rot (FER) and fumonisin contamination during artificially inoculated trials over two years. Furthermore, these FER-resistant inbred lines have been tested for resistance to other important maize ear rot diseases including Gibberella ear rot, Diplodia ear rot and Aspergillus ear rot in a multi-location field trial. Inbred lines with low and high levels of resistance to multiple infections were identified, but significant inbred x location interactions were observed. This suggests that potentially resistant lines will require further testing in an extra season to confirm their resistant status. If confirmed, these sources could be used to investigate the underlying mechanisms conferring resistance, or to develop molecular markers to facilitate the transfer of resistance into commercially valuable cultivars.