The common bean (Phaseolus vulgaris L.) is an important crop grown widely in Uganda. It is also an important source of income for smallholder farmers particularly women. Despite its importance, production in the cool highland regions is constrained by anthracnose disease which causes losses in both the quantity and the quality of beans produced. The principal aim of this research was to elucidate on the status of dry bean anthracnose and the genetics governing its resistance. A participatory rural appraisal study was conducted to explore farmers' knowledge, experience, problems and cultivar preferences in association with managing dry bean anthracnose disease. This study revealed that anthracnose is an important constraint to production which is not controlled in any way. Although farmers have varying cultivar preferences, they use mostly home saved seed and only 1% could access improved seed. The study suggested the need for practical approaches in the provision of quality anthracnose resistant seed in consideration of farmers' preferences and the dynamics of their rural livelihoods. A study was conducted to determine the variability of the anthracnose (Colletotrichum lindemuthianum) pathogen in some of the major bean growing regions of Uganda. Use was made of a set of 12 internationally accepted anthracnose differential cultivars to identify the physiological races present. The results obtained indicated the presence of eight races with one race (767) being dominant and most aggressive. Differential cultivars AB 136 and G2333 were resistant to all the eight races, and can be utilised as potential sources of resistant genes. A germplasm collection of mostly Ugandan accessions was screened for anthracnose resistance. Using the area under disease progression curve as the tool for assessing disease severity, eleven accessions were identified that posses good levels of anthracnose resistance. The yield loss attributed to the anthracnose disease was determined on three susceptible Ugandan market-class dry bean cultivars and two resistant cultivars. The results showed that the yield of susceptible cultivars was reduced by about 40% and an almost equivalent yield was lost due to poor quality seed. In comparison, the yield lost by the resistant cultivars was not significant. The study suggested the use of resistant cultivars as the best solution in combating anthracnose resistance. Three susceptible Ugandan market class dry bean cultivars and six resistant cultivars were used for the study of the inheritance of resistance to the anthracnose pathotype 767 in a complete 9x9 diallel design. The results clearly indicated that the resistance was predominately conditioned by additive gene action. It was also established that epistatic gene action was important. More than one pair of genes displaying partial dominance were responsible for determining resistance and the maternal effect did not have an influence on resistance. Additionally, the result showed that some of susceptible cultivars combined very well with the resistant cultivars and that anthracnose resistance heritability estimates in both the narrow and broad sense were high. These results suggested that the use of simple pedigree breeding procedures such as backcross selection could be useful in improving anthracnose resistance levels in the Ugandan market class varieties. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

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.