Genetic analysis of resistance to common bean rust disease in Uganda

Bean rust caused by Uromyces appendiculatus (Pers., Pers) Unger. is one of the major foliar diseases of common bean in Uganda. In the case of Uganda the framers’ preferred cultivars were from the Andean (small-seeded) cultivars which were susceptible to bean rust. Breeding for rust resistance is considered the most economical, practical and effective management option for this disease. The sources of bean rust resistance identified in Uganda were of the Mesoamerican (small-seeded) and Andean (large-seeded) background. However, the combination of both gene pools is often incompatible. This study determined the combining ability of resistant cultivars of both the Mesoamerican and Andean genepool present in Ugandan bean population. Six resistant cultivars were used as males while four cultivars were used as females in a North Carolina II mating design and 18 F2 families were evaluated for rust disease severity. Results indicated that there was high significant difference (P<0.01) among the female and male parents studied for rust disease severity. The parent Redland Pioneer had the lowest negative GCA value (-0.34) and was the best combiner. Conversely, the parent NABE 21 had the highest positive GCA (0.21) and was the lowest combiner. The cross NABE 21x Mexico 309 had the most negative SCA value (-0.59) followed by NABE 16xOuro Negro (-0.43). These particular crosses would be useful in breeding programmes for resistance to bean rust in Uganda