Inheritance and selection for resistance to Angular Leaf Spot (Phaeoisariopsis Griseola (SACC)and common bacterial blight (Xanthomonas Campestris pv Phaseoli) in yellow beans

Abstract

Angular leaf spot (Phaeoisariopsis griseo/a) and common bacterial blight (Xanthomonas campestris pv phaseo/i) are two major diseases of common bean (Phaseo/us vulgaris L.). In Africa, the two diseases account for losses of 604,600 tons per year. High levels of cultivar resistance to the two diseases would minimise yield losses, reduce production costs and facilitate the production and distribution of pathogen-free seed. The objectives of this study were; 1) To determine the inheritance of resistance to angular leaf spot (in Mexico 54) 2) Determine the inheritance of resistance to common bacterial blight in Wilk 2 and VAX 6, and 3) to incorporate resistance to the two diseases into two susceptible but popular Zambian landraces, Lusaka Yellow and Pembela. The two susceptible bean genotypes were crossed with three other cultivars resistant to angular leaf spot and common bacterial blight. Six crosses were made: two between the angular leaf spot resistant parent and the susceptible landraces, and four with common bacterial blight resistant parents. F1, F2 and back crosses to both parents were generated in bi-parental crosses. The progenies and the parents were evaluated for resistance in the screen house and field at Kabete Field Station, University of Nairobi. These were inoculated with Phaeoisariopsis griseo/a isolate 63-55 for angular leaf spot and Xanthomonas campestris pv phaseo/i to determine the inheritance of the two diseases. Lusaka Yellow showed susceptible reaction to Phaeoisariopsis griseo/a isolate 63-55, confirming its susceptibility. All plants of Mexico 54 were resistant to the same isolate. All the F1were resistant to angular leafspot indicating that resistance was dominant. There was no significant deviation from the expected 3:1 ratio for resistance to susceptible in the F2 population, confirming that resistance to angular leaf spot was monogenic and dominant. The backcross to Lusaka Yellow showed a 1:1 segregation ratio while the backcrosses to Mexico 54 were all resistant. Inoculation of Pembela with isolate 63-55 showed that all plants were susceptible. In the cross Pembela x Mexico 54, all the F1 plants were resistant. F2 progenies segregated in a 3:1 ratio for resistant to susceptible. Backcross to Pembela gave a 1:1 ratio for resistant to susceptible. All backcrosses to Mexico 54 were resistant. The results confirmed that resistance to Inheritance to common bacterial blight was found to be dominant. All the plants of Wilk 2 and VAX 6 were resistant. Those of Lusaka Yellow and Pembela were susceptible. All the F1 in the four crosses for common bacterial blight were resistant. The F2 segregated in the 3:1 ratio for resistant to susceptible. Backcross to susceptible parents showed a 1:1 ratio for resistant to susceptible. Backcrosses to resistant parents were all resistant. Both additive and non additive gene effects were important sources of variability in plant height, number of pods per plant, pod length, number of pods per pod and grain yield.