Anthracnose is one of the serious diseases of cowpea (Vigna unguiculata L. Walp) and common bean (Phaseolus vulgaris L.) caused by the Colletotrichum fungi. The disease is prevalent is small holder farmers’ fields due to the scarcity and high cost of the synthetic fungicides. This study was conducted with the main aim of improving food security and income of the smallholder farmers by increasing legumes, P. vulgaris and V. unguiculata thereby increasing production and improve food security and income of smallholder farmers. Investigations involved in vitro bioassaying for antifungal activities of the crude extracts on Colletotrichum lindemuthianum (Sacc. and Magn.) Bri. and Cav. and Colletotrichum dematium (Fr.) Grove var. truncata field isolates and evaluating the effect of crude plant extracts seed treatments on seed germination, emergence and control of anthracnose disease of common bean and cowpea. Furthermore, ultra-structural changes of plant extracts treated and efficacy of foliar application of extracts. The in vitro study showed that Allium sativum L., Agapanthus caulescens Spreng., Carica papaya L. and Syzygium cordatum Hochst.ex Krauss extracts have good antifungal activities against both C. lindemuthianum and C. dematium. The low concentrations (5 mg.ml-1) of Syzygium and Agapanthus water extracts and acetone extracts of Agapanthus and Carica gave a high percentage of bean seed germination, emergence, short mean emergence time (MET) and were effective in controlling the anthracnose disease. The treatment of Agapanthus (both water and acetone) extracts also increased the shoot length and dry weight of the seedlings. The Allium acetone extracts (5 mg.ml-1) was the only treatment that gave good results with respect to germination percentages, MET, shoot length, leaf area and dry mass of cowpea. Five mg.ml-1 concentrations of Syzygium and Agapanthus water extracts and acetone extracts of Agapanthus and Carica have potential as seed treatments on bean. Allium acetone extract (5 mg.ml-1) was the only potential cowpea seed treatment that could be recommended to farmers as an alternative to the synthetic fungicide. Electron microscopy revealed that principle differences were observed in the cotyledon-embryo connecting tissues of seeds treated with Agapanthus, which had few cristae in their mitochondria than the cells from other treatments. The embryonic root cells of bean seeds treated with Agapanthus had coalescing protein bodies. The embryonic root cells of cowpea and bean treated with Syzygium had fewer lipid bodies as compared to the control and the Agapanthus treated seeds. Bean plants that were foliar treated with the 15 mg.ml-1 concentrations of Allium water, Agapanthus water, Carica water, Agapanthus acetone, Carica 5 and 15 mg.ml-1 acetone, Syzygium 5 mg.ml-1 acetone extracts and the combinations (2.5 mg.ml-1 + 2.5 mg.ml-1) of Allium + Agapanthus, Allium + Carica, Agapanthus + Syzygium and Carica + Syzygium extracts registered low anthracnose (C. lindemuthianum,) disease severity and high leaf area. The cowpea plants treated with 15 mg.ml-1 water extracts of Agapanthus and the combinations of Allium + Agapanthus, Agapanthus + Carica and Agapanthus + Syzygium extracts recorded low cowpea anthracnose (C. dematium) disease severity, highest leaf area and dry mass. The study revealed that A. sativum, Agapanthus, C. papaya and S. cordatum plant extracts have antifungal activities and can be used as alternative seed treatments and foliar fungicides against the anthracnose diseases of legumes (cowpea and common bean) instead of synthetic fungicides without causing any negative effect on seed germination, emergence, ultra-structure of seeds and plant growth. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Microbiology and Plant Pathology / Unrestricted

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Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 74-82). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 74-82). Also available on the Internet.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2018-09-19T11:12:48Z No. of bitstreams: 1 texto completo.pdf: 1966574 bytes, checksum: 9a74f6b3cb6b04d280008a26f090b161 (MD5) / Made available in DSpace on 2018-09-19T11:12:48Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1966574 bytes, checksum: 9a74f6b3cb6b04d280008a26f090b161 (MD5) Previous issue date: 2017-02-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A cultura do feijoeiro comum no Brasil, além do imenso valor que representa na cadeia econômica e para milhares de agricultores no país, é fundamental devido à contribuição que possui na segurança alimentar da população. Cultivares com evento de resistência ao Bean golden mosaic virus (begomovirus), vírus responsável por causar uma das doenças que mais afeta a produtividade da cultura no país, foram desenvolvidas após vários anos de pesquisas. Infecções durante testes em campo desses materiais por outro vírus, o Cowpea mild mottle virus (carlavirus), gerou novas preocupações tanto aos pesquisadores envolvidos no projeto do feijoeiro resistente ao mosaico dourado quanto aos produtores que aguardavam a liberação comercial dessas cultivares. Apesar de alguns trabalhos já terem sido desenvolvidos a fim de se avaliar os prejuízos produtivos que o CPMMV causa sobre as isolinhas transgênicas de feijoeiro, assim como sua distribuição, nenhum conhecimento se tem sobre a diversidade desse vírus em feijão comum ou transgênico no Brasil, e poucos trabalhos dessa natureza são encontrados na literatura até hoje. Nesse trabalho, buscou-se avaliar a variabilidade de populações do CPMMV para cada uma de quinze cultivares de feijoeiro comum, sendo dez transgênicas (resistentes ao BGMV) e cinco convencionais, em um campo experimental com ocorrência e transmissão natural do CPMMV. Também foram quantificados os níveis virais em cada cultivar a partir de três repetições. Para cada uma das quinze plantas representando 15 diferentes genótipos de feijoeiro comum, o genoma completo de cinco isolados de CPMMV foi sequenciado pela montagem de sequenciamentos de blocos de PCR. Diferenças foram encontradas na variabilidade dos cinco isolados de CPMMV em plantas transgênicas e em plantas convencionais. Os valores dos descritores de variabilidade π, S, K e Θ foram geralmente maiores nos grupos de isolados de plantas transgênicas. Isso se repetiu para todas as ORF’s virais analisadas. As ORF’s 2, 3 e 4 foram as que tiveram a maior diversidade registrada, enquanto que a diferenças entre os grupos já citados foi mais perceptível nas regiões das ORF’s 2, 5 e 6. Eventos de recombinação foram encontrados na ORF 1 viral, quase sempre ocorrendo em isolados de plantas transgênicas, assim como alguns na ORF 2 e 6. Analisando as sequencias da ORF 1, nota-se que os cinco isolados de cada planta se agrupam e tendem a formar clados próximos a grupos de isolados de genótipos hospedeiros similares, o que pode decorrer da interação entre a replicase viral e a planta. Para a região 3’ do genoma, houve a separação do conjunto de 75 isolados em dois grupos de variantes. A identidade nucleotídica par a par entre isolados de grupos distintos variou entre 75 e 85%. Pelos testes de seleção, existe evidência significativa de que vária populações virais estão sobre processo de seleção não neutra. O acúmulo viral não teve diferença significativa entre plantas transgênicas e convencionais. A quantificação também não revelou diferenças em níveis virais em plantas transgênicas originadas de retrocruzamentos com a cultivar Pérola em comparação aos níveis naquelas retrocruzadas com a cultivar BRS Pontal. Os resultados desse trabalho reforçam resultados anteriores de que dois grupos de estirpes de CPMMV estão distribuídos pelas regiões produtoras brasileiras, provavelmente pela presença em plantas daninhas (onde a variabilidade desse vírus nunca foi analisada) e em hospedeiros cultivados como o próprio feijoeiro. Também comprova a alta variabilidade desse vírus de RNA, principalmente nas novas cultivares de feijoeiro resistente ao mosaico dourado por transgenia. É provável que a presença de BGMV nas cultivares convencionais e consequentemente a infecção mista dos dois vírus tenha algum efeito sobre os valores de variabilidade apresentados nesse estudo. Os mecanismos moleculares dessa interação, porém, não são conhecidos. Os resultados apresentados e o fato de que hospedeiros não cultivados estão distribuídos por grandes áreas de produção e que estes podem atuar como reservatório viral, além da grande distribuição da mosca branca pelo Brasil, fazem com que novos trabalhos com esse patógeno sejam de extrema importância. / The common bean crop in Brazil, besides its economic importance, represents a major source of what is daily consumed by Brazilian population in terms of proteins and carbohydrates, contributing to food security. Cultivars with a transgenic resistance event to Bean golden mosaic virus (begomovirus), a virus that causes one of the most important diseases of common bean, were developed after many years of research. The release of these cultivars immune to BGMV is undergoing difficulties because of the re-emergence of Cowpea mild mottle virus (carlavirus) in common bean, which has raised some concerns for the researchers and the growers. Although works to access the damage potential into different genotypes of these resistant isolines and to investigate the virus distribution are being reported, no study is found evaluating CPMMV molecular characteristics and diversity in transgenic as well as conventional common bean cultivars in Brazil. In fact, there are very few studies of this kind globally. The objective of this work was to evaluate the variability on CPMMV populations from each of the fifteen common bean cultivars, ten transgenic and resistant to BGMV, and five conventional cultivars, from a field experiment with natural CPMMV transmission by whitefly. CPMMV was also quantified on the three plant replicates of each genotype. Five CPMMV isolates were completely sequenced on all fifteen plants with different genotypes, providing 75 full virus genomes after assembly of PCR sequence blocks. Differences in variability were found between those groups of isolates from transgenic plants to those from conventional ones. With the π, S, K, and Θ-W descriptors, we detected a considerable higher CPMMV variability within transgenic plants in comparison to the virus variability within conventional cultivars in most of the cases. This was the case for all analyzed ORF’s. The ORF’s 2, 3 and 4 were the ones with the highest variability in the genome; at ORF’s 2, 5, and 6, the differences in variability mentioned above are most discernible. Recombination events between isolates happening at the ORF 1 region were detected, as well as at ORF 2 and at ORF 6. Mostly of these were between isolates from transgenic plants. The phylogenetic analysis with ORF 1 sequences of all seventy-five isolates reveals the formation of groups based on host genotypes, and that these groups are most likely grouping near a cluster of isolates from a similar host plant genotype. These could be the result of the direct and specific interactions needed between the viral replicase and the plant. The results of phylogenetic analysis and sequence comparisons with the 3’ region of the viral genome (ORF 2-6), divided the 75 isolates of this study into two groups of CPMMV variants. The pairwise nucleotide differences between isolates from distinct groups ranged from 75 to 85%. The selection tests at some ORF’s give significant evidence that some populations are evolving under a non- random process. The viral accumulation on conventional cultivars did not differ statistically to the accumulation at transgenic plants. In addition, there is no evidence of differences between CPMMV levels at transgenic cultivars that have Pérola as the reccurent parent to those that have the BRS Pontal. The results from this work corroborate with previous studies that indicate the existence of two CPMMV strains naturally distributed in Brazilian production areas. It also confirms the expected high variability potential of this RNA virus; the high variability registered on the newly developed BGMV-resistant transgenic common bean cultivars is also troublesome. The presence of BGMV in mixed infections with CPMMV at conventional cultivars is probably influencing the results of CPMMV variability, but the molecular properties of this interaction is still unknown. These results, in addition to the fact that non-cultivated host plants are distributed along major production areas and may act as viral reservoirs and the known widespread of whiteflies in growing regions of Brazil, make further studies with this pathogen of fundamental importance.

Thesis (M. Sc.(Agronomy)) -- University of Limpopo, 2015 / Cowpea (Vigna unguiculata L. Walp) is an important grain legume grown in many parts of the world mostly by smallholder (SH) farmers. Low soil phosphorus (P) and drought stress are major constraints to legume production and threaten food security. Root architecture is a spatial configuration of the root system which is influenced by moisture status and P uptake. A field experiment was conducted at Ukulima farm near Modimolle in Waterberg district during 2012/13 summer growing season. The treatments comprised of two levels each for soil P (low and high) and moisture status (water stress and well-watered); and eight cowpea genotypes (Tvu 4632, Tvu 6365, Tvu 9848, Tvu 15445, Tvu 16408, Tvu 15143, Oloyin and IT00K-1217). The low P level implied the available P in the soil measured in situ, which was less than 8 mg kg-1 while the high P level entailed fertilization at the rate of 40 kg P ha-1 application to achieve approximately 35 mg P kg-1 of soil . The root traits measured included angle of adventitious and basal roots, number of basal roots, tap root diameters at 5, 10, 15 and 20 cm soil depths; lateral branching densities at depth 5,10 and 15 cm, nodule score, deep score, shallowness score, 3rd order branching density, and 1.5 branching densities at 5 and 10 cm depth. Plant parameters measured were plant height, number of pods per plant, number of seeds per pod, length of the pods, unshelled weight, shelled weight and number of primary and secondary branches. Photosynthetic parameters measured were photosynthetic rate, intercellular CO2 concentration, water conductance, transpiration rate, vapour pressure deficits, sample cell CO2, sample cell H2O and relative humidity in the cell. All treatment factors were combined as split-split plot arrangement fitted into randomized complete block design; with four replicates. Results indicate that the lateral root branching density at 5 and 10 cm differed significantly (P≤0.05) across cowpea genotypes. Genotype showed significant effect on taproot diameter at 10 cm. Moisture status and P level exerted significant effect on cowpea genotypes 15 cm. There were significant differences (P≤0.05) for lateral root branching density observed at 5 and 10 cm depth in P rates x genotype interaction. Statistical analysis showed that P levels and cowpea genotypes had significant effects (P≤0.05) on mean plant height, biomass and highly significantly effects (P≤0.01) on number of branches, days to physiological maturity and mean pod length. The interaction between cowpea genotype and moisture stress condition significantly (P≤0.05) affected hundred (100) seed weight. Cowpea genotype Tvu16408 obtained highest grain yield of 3240 kg ha-1 and lowest was by IT00K1217 which obtained grain yield of 1256 kg ha-1. Results showed that photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O, relative humidity in the cell, intercellular CO2 and vapour pressure deficit differed significantly (P≤0.05) across cowpea genotypes. Soil moisture condition and cowpea genotype exerted significant (P≤0.01) effect on photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O and relative humidity in the cell. Variation in P levels had no significant effect on the measured photosynthetic parameters. Oloyin genotype had the highest photosynthetic rate followed by Tvu 4632 while cowpea genotype Tvu 9848 had the least photosynthetic rate. Interaction of moisture stress and cowpea genotype had a significant effect on intercellular CO2 concentration. Water stress reduced the intercellular CO2 concentration of Oloyin, Tvu 6365 and 4632 but resulted in a significant increase in intercellular CO2 concentration in Tvu 9848 genotype. Results showed that variation in soil P level exerted a significant (P≤0.05) effect on grain tissue P content and uptake, and a highly significant (P≤0.01) difference in P content across the various cowpea genotypes. Moisture stress exerted a significant (P≤0.05) difference on P uptake. The results showed that P levels and cowpea genotype variation exerted significant (P≤0.05) effects on P content, P uptake and nitrogen (N) uptake. Moisture status and cowpea genotype variation exerted significant (P≤0.05) effects on total N and N uptake. Cowpea genotype Tvu 9848 obtained more total N content (4.37%), while the lowest total N content was obtained by cowpea genotype Tvu 15445 with 3035 mg kg-1. The interaction between cowpea genotype and moisture status exerted a significant (P≤0.05) effect on N and P uptake of immature green pods harvested. There is a need to conduct more studies to identify cowpea genotypes, their root architecture and agronomic measures that can do well under xvii drought stress and low soil P conditions. Research needs to be conducted to enhance cowpea productivity under both low soil P and drought stress. Keywords: cowpea genotypes; moisture stress; phosphorus fertilisation; root traits

Thesis (M. Sc. Agriculture (Agronomy)) -- University of Limpopo, 2019 / Cowpea (Vigna unguiculata) is a multi-purpose crop as it can be used for human consumption and livestock feeding. Cowpea serves as one of the cheapest sources of vegetable protein as the dry grain contains 25-30% protein. Its ability to tolerate drought and fix atmospheric nitrogen makes it suitable for marginal areas with low rainfall and poor soil fertility. However, low cowpea yields are common in Limpopo province due to shortage of improved varieties and lack of good seed for planting. The objectives of the present study were to determine growth, yield components and grain yield of elite cowpea genotypes across two locations and seasons, and to determine grain yield and yield components stability of the elite cowpea genotypes across the environments. The experiments were conducted at the University of Limpopo Experimental farm (Syferkuil) in Mankweng and Towoomba Research Station located in Bela-Bela, Limpopo Province during 2015/16 and 2016/17 growing seasons. The trials were carried out in a randomized complete block design (RCBD) consisting of three replications. Ten elite cowpea breeding lines (L1-L10) and a control check Bechuana White (BW) were planted at inter-row and intra-row spacings of 1 m and 0.3 m, respectively, in two rows of 6 m length. Round-up (isopropylamine salt of glyphosate) and Dual (S-metalachlor) at the rate of 3 L/ha and 0.5 L/ha, respectively, were used to control weeds at planting. Insecticide Karate (lambda-cyhalothrin) and Aphox (pirimicarb) at the rate of 1 L/ha and 500 g/ha were applied to control aphids, pod borers and other insects. Initial soil sampling was done at the depth of 0-20 cm to determine soil pH, organic matter, nitrate, ammonium, phosphorus and soil particle size. Agronomic data collected included number days to 50% flowering, number of days to 90% maturity, canopy width, plant height, peduncle length, number of pods per plant, pod length, hundred seed weight, fodder and grain yield. The collected data were subjected to analysis of variance using SAS software to determine the performance of the cowpea genotypes across the two locations and seasons. Means showing significant differences were separated using Duncan Multiple Range Test at the probability level of 5%. Data for number of days to 90% maturity, grain and fodder yields were further subjected to stability analysis through GGE biplot using Genstat software application. The results showed statistical differences for most of the studied traits as affected by genotype, location, seasonal effects and their interactions. Among the genotypes, average number of days to 50% flowering ranged from 53 to 60 days, while number of days to 90% maturity ranged from 89 to 96 days, with line L9 being the earliest to flower and mature. Tall plants were given by Line L5 (48.94 cm), followed by L7 (48.72 cm) and L10 (48.35 cm). Breeding line L7 recorded long peduncles with a mean of 36.37 cm. Number of pods per plant had a range of 16.00 to 25.52, while pod length varied from 14.46 to 17.63 cm, with line L7 having the highest number of pods per plant with long pods. Line L3 produced least number of pods per plant and shorter pods. Local check BW produced more number of seeds per pod as compared to all the breeding lines with a mean of 12.89 seeds/pod. One hundred seed weight varied from 15.67 g to 22.70 g among the genotypes. Grain yield among the genotypes ranged from 1441.20 to 2595.20 kg/ha with the best yielder being line L7, which was followed by line L2 (1928.00 kg/ha), L10 (1891.70 kg/ha) and Local variety BW (1858.70 kg/ha). The least grain yield was observed for line L8. Among the locations, Towoomba had significantly higher grain yield than Syferkuil with mean values of 1604.20 and 1982.20 kg/ha respectively. Significantly higher grain yield was recorded in 2016/17 season with a mean value of 1854.80 kg/ha than 2015/16 season (1732.30 kg/ha). Fodder yield ranged from 1934.20 to 3611.00 kg/ha, with line L3 being the highest yielder and it was followed by line L10 with an average of 3022.00 kg/ha. Local check BW produced the least fodder yields. The GGE biplot showed that lines L2, L9 and L4 matured earlier than all other lines including local variety BW and were stable across locations and seasons in terms of maturity. The biplot identified breeding lines L7, L2, L10 and Local check BW as the highest grain yielders but only line L7 and L2 were stable across the two locations and seasons. Lines L4, L10, L3, and L2 were the highest fodder yielders but only line L2 was stable across locations and seasons. Therefore, breeding lines L7 and L2 are recommended for both grain and fodder yield in both locations. Key words: cowpea, elite, breeding line, location, seasons, grain yield and stability.