Breeding dry bean for resistance to bacterial brown spot disease conditions in South Africa.
Salegua, Venancio Alexandre.
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Bacterial brown spot (BBS) disease is a major disease in dry beans in South Africa causing yield losses of up to 55%. The overall goal of the research was to improve dry bean production through identifying high yielding and stable cultivars, with resistance to the BBS disease, classifying or detecting mega environments for dry bean production and to conduct prebreeding trials that will provide information that will contribute to BBS disease breeding in South Africa. Four hundred and twenty three Andean Diversity Panel (ADP) dry bean genotypes were screened for grain yield and BBS disease resistance in three regions. The plants were inoculated with three isolates of BBS strains or inoculum at 21, 28 and 36 days after planting. Disease severity was rated at 7, 14 and 21 days after the first infection and the relative area under disease progress curve (RAUDPC) was calculated. The analysis of variance revealed significant differences (P<0.001) in grain yield and BBS severity for genotype, environment and genotype by environment interaction (GEI). Genotypes were classified as resistant, moderate resistant and susceptible based on BBS severity and RAUPDC. The study identified 21.0% of the genotypes as resistant and 41.6% as moderately resistant to BBS disease. The RAUDPC was significantly (P<0.001) negatively associated with grain yield (r= -0.55). The small seeded genotypes showed lower RAUDPC than the medium and the large seeded, and genotypes with an indeterminate growth habit showed lower RAUDPC than those with a determinate growth habit. Genotypes ADP-0592, ADP-0790, ADP-0120 and ADP-0008 were selected for both resistance to BBS disease resistance and high seed yield across three environments. The best genotypes had grain yield above 1.45 t ha-1 across sites, and above1.85 t ha-1 at individual sites, and had grain yield above the grand mean (0.87 t ha-1) and the best performing cultivar (1.13 t ha-1), and mean BBS severity below the grand mean (39.85) and the best performing cultivar (31.67). These genotypes can be useful sources of genetic resistance for future dry bean improvement.