Managing Angular Leaf Spot on Common Bean in Africa by Supplementing Farmer Mixtures with Resistant Varieties. Mukishi M. Pyndji, Programme National Legumineuses du Zaire (PNL), BP 496, Bukavu, Kivu, Zaire. Peter Trutmann, Centro Internacional de Agricultura Tropical (CIAT), Apartado Aereo 6713, Cali, Colombia. Plant Dis. 76:1144-1147. Accepted for publication 7 March 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1144.

The effectiveness of supplementing local bean (Phaseolus vulgaris) mixtures with varieties resistant to angular leaf spot, caused by Phaeoisariopsis griseola, was evaluated in the Great Lakes region of Africa. The severity of angular leaf spot was lower (P = 0.05) in farmer mixtures supplemented with 25% or more of resistant lines BAT76 or A285 in three of four seasons than in mixtures without resistant lines. Significant decreases in angular leaf spot severity were also obtained in the new mixtures when measuring both original farmer and new resistant lines. The results suggest that important foliar diseases can be controlled with modern plant breeding products in systems where varietal mixtures predominate through supplementation rather than displacement of existing genetic diversity by new varieties. However, the supplementation strategy is also limited, because its indiscriminate use in managing multiple diseases could lead to severe erosion of local genetic diversity.