Pepper (Capsicum annuum L.) is an important vegetable crop grown and consumed worldwide. Potato virus Y (PVY) is a globally economically important pathogen which significantly reduces the yield and quality of cultivated pepper. The virus is considered as a major limiting factor to the economic production of pepper in the province of KwaZulu-Natal (KZN) in the Republic of South Africa (RSA). Many applied practices to control the spread of PVY are ineffective to mitigate the losses incurred by many farming communities across the KZN province. Therefore, the objectives of this study was to determine the full genome sequence of a PVY isolate from KZN, to identify resistance alleles in commercially available pepper varieties in KZN and to develop a pepper hybrid variety with resistance to PVY using a molecular breeding strategy The first part of the study was conducted to determine the first full genome sequence of a PVY isolate (JVW-186) infecting pepper from KZN. The complete genome sequence of JVW-186 was assembled from overlapping RT-PCR clones using MEGA 5 software. Individual ORFs were identified using the nucleotide data base NCBI and aligned using CLUSTALW. RDP4 software was used to identify recombination junctions in the sequence alignment of JVW-186. CLC Main Workbench 6 software was used to determine the nucleotide sequence similarity of recombinant and non-recombinant fragments of JVW-186 in conjunction with ten PVY parental isolates. Based on sequence data, virus morphology and the coat protein size as determined by SDS-PAGE analysis, the identity of the isolate JVW-186 was confirmed as PVY. Phylogenetic trees were constructed from all recombinant and non-recombinant segments of the sequence by the maximum likelihood method using MEGA 5 software. The full length sequence of JVW-186 consisted of 9700bp. Two ORF’s were identified at position 186 and 2915 of the sequence alignment encoding the viral polyprotein and the frameshift translated protein P3N-PIPO, respectively. RDP4 software confirmed two recombination breakpoints at position 343 and 9308 of the sequence resulting in four segments of the genome. At each recombination event, a 1021-bp fragment at the 5’ end in the region of the P1/HC-Pro protein and a 392-bp fragment in the region of the coat protein shared a high sequence similarity of 91.8 % and 98.89 % to the potato borne PVYC parental isolate PRI-509 and the PVYO parental isolate SASA-110 respectively. The non-recombinant fragment 1 clustered within the C clade of PVY isolates; however the large 7942-bp fragment 3 did not cluster within any of the clades although it shared > 80% nucleotide sequence similarity to other PVY isolates used in this study. Our results suggest that isolate JVW-186 is a novel recombinant strain of PVY that could have evolved due to the dynamics of selection. The second part of the study aimed to evaluate different pepper lines for resistance to PVY. Two recessive alleles (pvr21 and pvr22) located on the pvr2-elF4E locus are known to confer resistance to the virus. To this end, six pepper lines were challenged with PVY infected Nicotiana tabacum cv. Xanthi leaf material using mechanical inoculation under greenhouse conditions. Each line was assessed for resistance to PVY by visual screening for disease severity and quantitative enzyme linked immunosorbent assay (ELISA) for virus load. Pepper lines were further characterized using tetra-primer ARMS-PCR (amplification refractory mutation system polymerase chain reaction) to identify and differentiate the presence of homozygous/heterozygous resistance alleles that confer PVY resistance. Evaluations revealed two resistant pepper lines (Double Up and Cecelia) and varying levels of susceptibility in the other four pepper lines challenged with PVY. The most susceptible pepper line was Benno, although high levels of susceptibility were observed in three other lines (IP, Mantenga and Excellence). The pvr2+ allele was positively identified in all the susceptible pepper lines using the T200A tetra-primer which confirms that the presence of this allele is dominant for PVY susceptibility. Double Up and Cecelia were genotyped homozygous pvr21/pvr21 and pvr22/pvr22 respectively, and remained asymptomatic throughout the trial which indicates that these alleles confer resistance to the isolate of PVY used in this study. The information generated in this study can be incorporated into breeding programs intended to control PVY on pepper in KZN. The final part of the study focused on the development of resistant varieties as the best alternative to manage PVY diseases on pepper. Homozygous F2 pepper lines were developed from local germplasm carrying PVY resistance genes (pvr21 and pvr22) using marker assisted selection (MAS). The F1 progeny was obtained by crossing a homozygous pvr21 (resistant) ‘Double Up’ cultivar with a heterozygous susceptible (pvr2+/pvr22) ‘Benno’ cultivar. F1 and F2 generations were assessed for the presence of PVY resistance/susceptibility alleles (pvr2+/pvr21/pvr22) at the pvr2-elF4e locus using the tetra primer amplification refractory mutation system – polymerase chain reaction (ARMS-PCR) procedure. Negative selection was carried out using the tetra-primer T200A marker to detect the pvr2+ (susceptible) allele. All F1 progeny displaying the pvr2+ allele were eliminated from further study. All 302 plants belonging to 29 F2 families expressing homozygous recessive traits were tested via mechanical inoculation for their response to PVY infection and resistance to PVY was confirmed in all selected families based on symptomatology in greenhouse house screens using double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA). These results show that ARMS-PCR can be used to successfully screen pepper genotypes for alleles that confer PVY resistance thereby contributing to the improvement of pepper production using molecular breeding approaches. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Made available in DSpace on 2014-06-11T19:28:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-26Bitstream added on 2014-06-13T19:58:14Z : No. of bitstreams: 1 000754266.pdf: 1934909 bytes, checksum: e561fe663a3222db7f013bbec7d20de0 (MD5) / O Brasil se destaca como um importante produtor de feijão (Phaseolus vulgaris). Porém, o ataque de diversos insetos-praga tem comprometido sua produtividade a campo. A lagarta-falsa-medideira, Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), é considerada uma espécie de importância crescente para a cultura do feijão, devido aos danos ocasionados nas últimas safras. Diante disso, surge a necessidade de estudar métodos de controle complementares ao método químico convencional, que apresentem eficiência e ao mesmo tempo, sejam menos agressivos ao meio ambiente. O presente trabalho teve como objetivo avaliar diferentes genótipos de feijoeiro, visando à seleção de materiais resistentes frente ao ataque de C. includens. Inicialmente, foram realizados testes preliminares com 59 genótipos, os quais foram divididos em três grupos, de acordo com a coloração das folhas (escura, clara e intermediária). A antixenose (oviposição) foi avaliada em teste com chance de escolha. Foram selecionados 12 materiais com potencial para resistência e dois padrões comerciais suscetíveis, para as etapas subsequentes. Com esses genótipos foram realizados ensaios de antixenose (oviposição), no interior de casa de vegetação, além de atratividade, antixenose (alimentação) e biologia com lagartas, em condições de laboratório (T= 26 ± 2º C, UR= 65 ± 10 % e fotoperíodo= 14 h). Com relação à oviposição de C. includens em teste sem chance de escolha, os genótipos ‘IAC Jabola’, Arcelina 1, ‘IAC Boreal’, ‘Flor de Mayo’ e ‘IAC Formoso’ apresentaram resistência do tipo antixenose (oviposição). Discos foliares dos 14 genótipos avaliados foram igualmente atrativos a lagartas de terceiro ínstar após seis horas de exposição. Em testes com e sem chance de escolha, os genótipos Arcelina 4, 2 ‘BRS Horizonte’, ‘Pérola’, H9A102-1-1-1-52, ‘IAC Boreal’, ‘IAC Harmonia... / Brazil is one of the biggest producer of common bean (Phaseolus vulgaris), but the attack of several insect pests has compromised their productivity in the field. The soybean looper Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) species is considered to be of increasing importance in growing bean due to the losses caused in the last harvests. Therefore, it is necessary to study additional control methods to the conventional chemical one, which is both efficient and less harmful to the environment. The objective of this paper is to evaluate different genotypes of bean aiming at the choice of materials resistant to the attack of C. includens. At first, preliminary tests were performed with 59 genotypes which were divided into three groups according to the color of the leafs (dark, light, and intermediate). The antixenosis (oviposition) was evaluated in a test with choice chance. 12 materials with potential to resistance and two susceptible commercial standards were selected for the following steps. With such genotypes antixenosis (oviposition) assays were performed inside the greenhouse, in addition to assays of attractiveness, antixenosis (feeding), and biology with loopers in lab conditions (T= 26 ± 2º C, RH= 65 ± 10 % and photoperiod = 14 h). Regarding oviposition of C. includes in a test without choice, the genotypes ‘IAC Jabola’, Arcelina 1, ‘IAC Boreal’, ‘Flor de Mayo’, ‘IAC Formoso’, ‘Rubi’, and ‘IAPAR 44’ presented resistance type antixenosis (oviposition). After six hours of exposure, leaf discs of 14 genotypes evaluated were equally attractive to third instar loopers. In tests with and without choice chance, the genotypes Arcelina 4, ‘BRS Horizonte’, ‘Pérola’, H9A102-1-1-1-52, ‘IAC Boreal’, ‘IAC Harmonia’, and ‘IAC Formoso’ were less consumed by third instar loopers. In the biology assay, the genotypes ‘IAC Boreal’, ‘IAC Harmonia...

The objective of this research was to investigate the occurrence of mycoflora in rice plants and rice seeds in South Africa and their negative impact. A total of six species of Fusarium were isolated from diseased rice plants and rice seeds and identified as F. anthophilum, F. chlamydosporum, F. compactum, F. equiseti, F. fujikuroi and F. semitectum. In the translation elongation factor data set, Fusarium equiseti isolates grouped together within the F. incarnatum - equiseti Species Complex (FIESC). The isolates from rice clustered together in a single clade with the F. equiseti and F. incarnatum isolates forming two separate sub-clades.The isolates of F. equiseti present a new phylogenetically distinct species in FIESC. In the pathogenicity tests, isolates of both F. anthophilum and F. fujikuroi caused bakanae disease to rice plants. Fifty four rice cultivars and lines were tested by the standardized test tube inoculation method for resistance and susceptibility against bakanae isolate of F. anthophilum and the bakanae isolate of F. fujikuroi. None of the rice cultivars and lines was found to be resistant to bakanae isolates of Fusarium spp. The fungicide, benomyl was found to be most effective as a seed treatment for controlling bakanae disease of rice due to isolates of both F. anthophilum and F. fujikuroi. Thiram was found to be the least effective fungicide for controlling bakanae disease of rice caused by isolates of both the Fusarium spp. Apart from Fusarium species, other fungi that were also isolated from diseased rice plants and rice seeds were identified as Alternaria alternata, Alternaria longipes, Cochliobolus miyabeanus, Nigrospora sphaerica, Phoma eupyrena, Phoma jolyana, Phoma sorghina and Pithomyces sp. In mycotoxin tests, the isolates of both F. anthophilum and F. fujikuroi produced moniliformin. None of the isolates of F. anthophilum and F. fujikuroi produced fumonisins. This research is important as it identifies many fungal species in rice plants and seeds in South Africa for the first time. Currently, there is very little literature that makes reference to such findings under South African conditions. In addition, this investigation unravels previously unknown information on the resistance of rice to bakanese disease. Finally, information is provided on the effectiveness of commonly used fungicides (benomyl and thiram) to control rice diseases. This knowledge is crucial information that is useful to plant pathologists, the farming community and the scientists that are involved in strategies of fighting or reducing rice diseases so as to help contribute to food security. / Environmental Sciences / D. Phil. (Environmental Science)

Made available in DSpace on 2014-06-11T19:35:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-12-12Bitstream added on 2014-06-13T19:24:11Z : No. of bitstreams: 1 000754014.pdf: 1942424 bytes, checksum: 471e068ee68e37f4b3c0be947e861dc1 (MD5) / No Brasil a soja, Glycine max (Linnaeus) Merril, é a principal oleaginosa, responsável pela geração de divisas, além de ser a principal cultura produtora de óleo vegetal e representar importante fonte de proteínas. Durante o desenvolvimento, a cultura é atacada por inúmeros insetos-praga, com destaque para a lagarta-falsa-medideira, Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), que tem causado danos às plantas durante a fase vegetativa e reprodutiva. Os sojicultores têm como a base para o controle dessa praga a aplicação de produtos químicos, os quais têm elevado o custo de produção. Considerando-se a importância desse inseto para a cultura da soja, aliado aos efeitos indesejáveis decorrentes da aplicação intensiva de inseticidas químicos para o controle, este trabalho teve como objetivo avaliar genótipos de soja frente ao ataque de C. includens, visando verificar a expressão de resistência. Foram realizados ensaios com mariposas (atratividade e preferência para oviposição) em casa de vegetação e com lagartas (antibiose) em condições de laboratório (T= 26 ± 2ºC, UR= 65 ± 10% e fotoperíodo= 14 h), além de análises morfológica, física e anatômica das folhas de soja. Foram avaliados os genótipos: ‘IAC 17’, ‘IAC 18’, ‘IAC 19’, ‘IAC 23’, ‘IAC 24’, ‘IAC 100’, IAC 74-2832, IAC 78-2318, PI 171451, PI 229358, PI 227687, PI 274453, PI 274454, D 75-10169, L 1-1-01, ‘Coodetec-208’ e ‘Conquista’. A preferência para oviposição foi avaliada em testes com e sem chance de escolha no interior de casa de vegetação. A antibiose foi avaliada em laboratório (T= 26 ± 2ºC, UR= 65 ± 10% e fotoperíodo= 14 h) confinando-se lagartas de C. includens nos diferentes genótipos e avaliando-se a duração total da fase larval; a viabilidade larval (%); a viabilidade... / In Brazil, soybean, Glycine max (Linnaeus) Merrill, is the main oilseed, responsible for the generation of foreign exchange, besides being the main producing culture of vegetable oil and represent an important source of protein. During development, the crops are attacked by numerous insect pests, especially the soybean looper, Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), which has caused damage to plants during the vegetative and reproductive stage. Soybean farmers have as the basis for control of this pest the application of chemicals, which have high production costs. Considering the importance of this insect for the soybean crop, coupled with the undesirable effects of intensive application of chemical insecticides for control, this study aimed to evaluate soybean genotypes against attack C. includens, to check the expression of resistance. Trials with moths (attractiveness and preference for oviposition) under greenhouse and larvae (antibiosis) under laboratory conditions (T = 26 ± 2 º C, UR = 65 ± 10% and photoperiod = 14 h) were performed, and the analysis morphological, physics and anatomy of soybean leaves. Genotypes were evaluated: ‘IAC 17’, ‘IAC 18’, ‘IAC 19’, ‘IAC 23’, ‘IAC 24’, ‘IAC 100’, IAC 74-2832, IAC 78-2318, PI 171451, PI 229358, PI 227687, PI 274453, PI 274454, D 75- 10169, L 1-1-01, ‘Coodetec-208’ and ‘Conquista’. The oviposition preference was evaluated in tests with and without choice inside the greenhouse. The antibiosis was evaluated under laboratory conditions (T = 26 ± 2 º C, UR = 65 ± 10% and photoperiod = 14 h) confining larvae of C. includens in different genotypes and evaluating the total duration of the larval...

Root rot diseases of bean (Phaseolus vulgaris L.) are a problem wherever they are grown, and are a major constraint to dry edible and snap bean production. Root rot is a primary yield limitation of snap bean production in the US, especially within the top three snap bean producing states of Wisconsin, Oregon and New York. Bean root rot pathogens will be present by the end of the first season even when starting with clean ground. The decline in yield can be relatively slow, so growers might not notice or appreciate the hidden yield cost associated with root rot disease. Traditional methods for disease control such as fungicides, crop rotations, cover crops, seedbed preparations have been proven ineffective (either physically ineffective or economically unviable) against root rot. Therefore, genetic resistance is needed. In order to address the need for genetic resistance to root rot in snap beans, the highly root rot resistant line RR6950, a small seeded black indeterminate type IIIA accession of unknown origin, was crossed with OSU5446, a highly root rot susceptible determinate type I blue lake four-sieve breeding line to produce the RR138 recombinant inbred mapping population. In this study we evaluated the RR138 RI population in the F₆ generation for resistance to Fusarium solani root rot in Oregon and Aphanomyces euteiches root rot in Wisconsin. We also evaluated this population for morphological traits and root structural traits including pod height, pod width, pod length, pod wall thickness, strings, seed color, flower color, tap and basal root diameter, and root angle measurements. The RR138 population was also genotyped on the 10K BeanCAP Illumina Beadchip. The Single Nucleotide Polymorphism (SNP) data was used to assemble a high-density linkage map and Quantitative Trait Loci (QTL) for phenotypic data were evaluated. The linkage map produced from this study contained 1,689 SNPs across 1,196cM. The map was populated with 1 SNP for every 1.4cM, spanning across 11 linkage groups. Three QTL associated with A. euteiches root rot resistance were consistently expressed in 2011 and 2012 trials. A. euteiches QTL were found on Pv02, Pv04, and Pv06 and accounted for 7-17% of total genetic variation. Two QTL associated with F. solani were found in 2011 trial on Pv03 and Pv07, account for 9 and 22% of total genetic variation, respectively. We also found several QTL for morphological traits and root structural traits including QTL for pod fiber and pod height on Pv04, pod length on Pv01, strings on Pv01, taproot diameter on Pv05, and shallow basal root angle on Pv05, accounting for 21, 26, 12, 20, 11, and 19% of total genetic variation, respectively. QTL discovered from Oregon data for F. solani resistance did not cluster with QTL for A. euteiches root rot resistance. "SNP0928_7", was highly associated with F. solani resistance on Pv07 and "SNP0508_2", was highly associated with A. euteiches on Pv02. QTL and markers associated with QTL from this study will be of value to snap bean breeders developing root rot resistant lines with processing traits, and provide more information about targeting the mechanism of resistance. / Graduation date: 2013

Fusarium root rot (FRR) disease, caused by the fungus Fusarium solani f. sp. phaseoli (FSP), is an important soil-borne disease reducing common bean (Phaseolus vulgaris L.) yields, and hence food security, in Uganda and elsewhere in developing countries where the crop is grown without fungicides. The key aim of this study was to elucidate the significance of bean root rot (BRR), appraise methods for screening germplasm for resistance to FRR, determine the genotypic variability of resistance, and the inheritance of resistance to FRR in common bean. This information was deemed useful in devising an appropriate strategy for breeding FRR resistance in beans. A participatory rural appraisal (PRA) was conducted in south-western and eastern Uganda to ascertain farmers’ awareness of BRR and their influence on preferred bean varieties. Bean root rot is considered to be the most devastating and most recognised disease, especially in south-western Uganda. Control measures for BRR were very minimal, and in some cases, non-existent. Use of resistant varieties to control the disease was not evident, because the most popular varieties were susceptible to the disease. The resistant bean varieties currently available have undesirable characteristics such as small seed size, black seed and late maturity. Large-seeded bean varieties, even though cited as being more susceptible to BRR than the small-seeded varieties, are still very popular. The study highlighted the need for breeding FRR resistance in the large-seeded bean varieties that are highly preferred by farmers. Four isolates of FSP (FSP-1, FSP-2, FSP-3 and FSP-4) were tested for pathogenicity under screenhouse and laboratory conditions. In addition, three methods of storing and maintaining the viability of FSP isolates were appraised. The isolate FSP-3, was found to be the most pathogenic, resulting in 100% disease incidence on all bean varieties tested, with high severity scores. The potato dextrose agar (PDA) slants stored at 5oC were found to be the best method of storage for pathogenic isolates. The FSP-3 isolate was subsequently utilised for screening bean lines for resistance to FRR. The influence of soil composition, irrigation frequency, and inoculation technique on the severity of FRR was studied on six bean lines. Interactions of irrigation frequency, soil composition, and bean lines were not significant. The 50% swamp soil:50% forest soil composition and forest soil alone categorized the varieties most distinctly according to their reaction to FRR. Also, the best distinct classification for the varieties was obtained under treatments that were watered daily and once in a week. Based on economic considerations, the standard forest soil and daily irrigation were subsequently adopted for screening bean germplasm for resistance to FRR. It was also found that sorghum seed as a medium for pathogen inoculation was better than the agar slurry medium. One hundred and forty seven common bean varieties were evaluated for resistance to FRR (isolate FSP-3) under screenhouse conditions. In order to confirm this resistance, 46 common bean lines selected from the screenhouse trial were further evaluated using natural inoculum in a BRR-infested field. Forty-four varieties comprising ten large-seeded, four medium-seeded and 30 small-seeded varieties showed moderate resistance to FRR; but none were resistant or immune to the disease. Based on adaptability, eight moderately resistant varieties were selected for use as parents in the study of inheritance of resistance to FRR. A 12 x 12 diallel mating design was utilised to develop 66 F1 and F2 populations, plus their reciprocal crosses, with the aim of studying the mode of inheritance of resistance to FRR. The F1 and F2 progeny evaluations showed that FRR resistance was mainly governed by additive genes in most populations. However, there were a few crosses which displayed highly significant specific combining ability (SCA) effects, implying that dominant effects were important in some populations. Maternal effects were also highly significant at both the F1 and F2 generations, suggesting that resistance was modified by cytoplasmic genes. The non-maternal effects were also significant in some populations, suggesting that the cytoplasmic genes were interacting with nuclear genes. The number of genes governing resistance to FRR varied from two to nine among the eight sources of resistance. The allelism test of resistant x resistant populations, and the observation of continuous distributions of severity scores, suggested the presence of many loci governing FRR resistance in beans. Broad sense heritability of disease resistance varied from 0.22-0.69, while heritability in the narrow sense was estimated as 0.35-0.49 in the populations. These results suggested that selection and backcrossing to both parents would be the best breeding procedures for improving resistance in the popular large-seeded bean varieties in Uganda. However, there could be complications in breeding for resistance to FRR in beans, because resistance was modified by cytoplasmic gene effects and their interaction with nuclear genes in some of the populations. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Abstract not available. / Thesis (Ph.D)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Soybeans, Glycine max, are an economically and strategically important crop in South Africa (SA). In order to meet local demands, large imports of soybeans are required, e.g., in the 2005/2006 soybean production period, 842 107 tonnes of oilcake were imported. Due to an increase in soybean production throughout the world, diseases that affect this crop have also increased in incidence and severity. Sclerotinia sclerotiorum, the causal organism of sclerotinia stem rot (SSR), is an important yield limiting disease of soybeans, as well as numerous other crops. The pathogen was first reported in SA in 1979. However, it was only in 2002 that this fungus was considered a major pathogen of soybeans in SA. The research reported in this thesis was conducted to investigate the epidemiology of S. sclerotiorum and examine numerous potential control methods for this pathogen, i.e., resistant cultivars, biocontrol, chemical control and seed treatments. A S. sclerotiorum isolate was obtained from sunflowers in Delmas, Mpumulanga, SA, in the form of sclerotia. This isolate was cultured and sent for identification and deposition in the Plant Protection Research Institute collection. This isolate, in the form of mycelia, was used for the duration of the study. For epidemiology studies, the effect of temperature, leaf wetness duration (LWD) and relative humidity (RH) were examined for their effect on rate of pathogen development. Twenty four combinations of temperature (19°C, 22°C, 25°C and 28°C), LWD (24, 48 and 72 hr) and RH (85 and 95%) were investigated. No interaction between temperature, LWD and RH was found. Temperature alone was the only factor that affected disease development. At 22°C, the rate of pathogen development (0.45 per unit per day) was significantly higher than all other temperatures, indicating that this temperature is optimum for disease development. Thirteen different soybean cultivars, i.e., LS6626RR, LS6710RR, LS666RR, LS555RR, LS6514RR, LS678RR, Prima 2000, Pan 626, AG5601RR, AG5409RR, 95B33, 95B53 and 96B01B, commercially grown in SA were investigated for their reaction to S. sclerotiorum. Prima 2000, 96B01B, 95B33 and AG5409RR were considered to be the least susceptible as they showed a significantly low rate of pathogen development (0.28, 0.28, 0.24, 0.23 per unit per day, respectively) and produced a significantly low number of sclerotia (3.03, 3.42, 3.21, 2.38, respectively). LS6626R and LS666RR may be considered most susceptible because of their significantly high rate of pathogen development (0.45 and 0.42 per unit per day, respectively) and high sclerotia production (8.16 and 7.50, respectively). Regression analysis showed a positive correlation coefficient (R2=0.71) between rate of growth of the pathogen and number of sclerotia produced, indicating that a higher rate is associated with a higher number of sclerotia. In vitro dual culture bioassays were performed to identify the biocontrol mechanisms of the biocontrol agents, EcoT® (a seed treatment) and Eco77® (a foliar treatment), against hyphae and sclerotia of S. sclerotiorum. Ultrastructural studies revealed that mycoparasitism is the probable mode of action as initial signs of hyphae of EcoT® and Eco77® coiling around hyphae of S. sclerotiorum were observed. Surface colonization of sclerotia by hyphae of EcoT® and Eco77® was also observed. In vitro antagonism of EcoT® against S. sclerotiorum on soybean seed was performed to determine pre-emergence and post-emergence disease. There was no significant difference in percentage germination between seeds treated with EcoT® and plated with the pathogen, untreated seeds and no S. sclerotiorum, and the control (i.e. no EcoT® and no pathogen). However, percentage non infected seedlings from seeds not treated with EcoT® was significantly lower, suggesting that EcoT® may be successfully used as a seed treatment for the control of SSR. In vivo trials were performed to investigate the effect of silicon (Si) alone, and in combination with Eco77®, on the effect of the rate of disease development. Plants treated with Eco77® had a significantly lower rate of disease development (0.19 per unit per day for plants treated with Eco77® and S. sclerotiorum and 0.20 per unit per day for plants treated with Eco77®, S. sclerotiorum and Si), compared to plants not treated with Eco77® (0.29 per unit per day for plants treated with S. sclerotiorum and 0.30 per unit per day for plants treated with S. sclerotiorum and Si), regardless of the application of Si. Similarly, plants treated with Eco77® had a significantly lower number of sclerotia (0.46 for plants treated with Eco77® and S. sclerotiorum and 0.91 for plants treated with Eco77®, S. sclerotiorum and Si), compared to plants not treated with Eco77® (3.31 for plants treated with S. sclerotiorum and 3.64 for plants treated with S. sclerotiorum and Si). The significantly lower rate of disease development coupled with a significant reduction in sclerotia showed that Eco77®, and not Si, was responsible for reducing the severity of SSR. A strong positive correlation between rate of disease development and the number of sclerotia produced (R2=0.79) was observed. For the investigation of various fungicides for the control of S. sclerotiorum, in vitro trials to determine the potential of three different fungicides at different rates, i.e., BAS 516 04F (133 g a.i. ha-1), BAS 516 04F (266 g a.i. ha-1), BAS 512 06F (380 g a.i. ha-1) and Sumisclex (760 g a.i. ha-1) were initially conducted. The control (non-amended PDA) had a significantly higher area under mycelial growth curve (243.0) than all fungicides tested. BAS 516 04F (at both concentrations) and BAS 512 06F completely inhibited the mycelial growth of S. sclerotiorum. Sumisclex inhibited the fungus by 89.07%. For in vivo trials, preventative treatments, i.e., BAS 516 04F (133 g a.i. ha-1), BAS 516 04F (266 g a.i. ha-1), BAS 512 06F (380 g a.i. ha-1), curative treatment, i.e. Sumisclex (760 g a.i. ha-1) and a combination preventative/curative treatment, i.e., BAS 512 06F (380 g a.i. ha-1)/Sumisclex (570 g a.i. ha-1) were investigated. No significant difference in disease severity index (DSI) was found between fungicide treatments and the inoculated control. BAS 512 06F and BAS 512 06F/Sumisclex had significantly lower grain yields (6.09 g and 5.96 g, respectively) compared to all other treatments. There was a positive correlation coefficient (R2=0.76), between DSI and grain yield, indicating that a high DSI is correlated with low grain yield. Trials to evaluate the effect of commercially available and currently unregistered seed treatments for the control of S. sclerotiorum on soybean seeds in vivo and in vitro were performed. Seed germination tests were performed to determine if seed treatments had any negative effects on seed germination in vitro. All seed treatments tested, i.e., BAS 516 03F (8, 16 and 32 ml a.i. 100 kg-1 seed), BAS 512 00F (7.5, 15 and 32 ml a.i. 100 kg-1 seed), Celest XL (100, 125, 200 and 250 ml a.i. 100 kg-1 seed), Sumisclex (5 and 10 ml a.i. 100 kg-1 seed), Benomyl (150 g a.i. 100 kg-1 seed), Captan (240 ml a.i. 100 kg-1 seed), Thiulin (180 g a.i. 100 kg-1 seed) and Anchor Red (300 ml a.i. 100 kg-1 seed), showed no negative effect on seed germination. For in vivo trials, BAS 516 03F (16 and 32 ml a.i. 100 kg-1 seed), BAS 512 00F (7.5, 15 and 32 ml a.i. 100 kg-1 seed), Celest XL (100, 125, 200 and 250 ml a.i. 100 kg-1 seed), Sumisclex (5 and 10 ml a.i. 100 kg-1 seed), Benomyl and Anchor Red had significantly similar percent germination and percent seedling survival as the untreated/uninoculated control. These seed treatments should be recommended for the control of S. sclerotiorum, as they protected seed during germination and subsequent seedling development. BAS 516 03F (8 ml a.i. 100 kg-1 seed) should not be recommended for the control of SSR, as it gave the lowest percent germination and percent seedling survival. The results presented in this thesis have helped to identify optimal environmental conditions for the development of S. sclerotiorum, which is important for the development of forecasting models for disease control. The least and most susceptible cultivars of those tested have been identified. Biocontrol using Eco77® as a foliar application showed great potential. The effect of Si needs to be further investigated, including the testing of more frequent applications and higher concentrations. The fungicides tested in this research did not show any potential for the control of SSR. However, the spray programme tested is for the control of soybean rust (Phakopsora pachyrhizi), and was investigated for its potential for the control of SSR. The spray programme, fungicide application and rating scale needs to be modified, to determine the true potential of these fungicides for the control of SSR. Numerous seed treatments have shown potential for the control of seed infection by SSR. Due to difficulties in producing ascospores, which are the primary source of inoculum for this pathogen in the field, all studies in this research were conducted with mycelia and not ascospores. The production, collection and storage of ascospores needs to be thoroughly investigated, and research conducted with ascospores. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.