Development of leaf anthracnose and its effect on yield and grain weight of sorghum in West Africa

Leaf anthracnose (Colletolrichum graminicola) development and its effect on yield and grain weight were studied for three seasons between 1990 and 1992 on two inbred sorghum cultivars exposed to natural inoculum in Mali, West Africa. Infection on the susceptible, medium-maturing (70 to 80 days to 50% flowering) cultivar IS 18696 (race caudatum) increased gradually until anthesis, then increased rapidly so that most leaves were killed at physiological maturity. Development of the disease on the moderately resistant early-maturing (<70 days to 50% flowering) cultivar IS 25105 (race guineense) was slower even after anthesis than on IS 18696, and leaves were not killed at physiological maturity. Mean disease severities for 15 plants on a 1 to 6 scale at about 50% flowering for IS 18696 were 3.1, 4.0, and 3.4 in 1990, 1991, and 1992, respectively. In contrast, disease severities for IS 25105 at 50% flowering were 2.1 in 1990 and 1991, and less than 3.3 at 11 days after 50% flowering in 1992. Areas under the disease progress curve (AUDPC) for the three years were 61, 127, and 121 for IS 18696, and 47, 112, and 122 for IS 25105. Yield loss calculated from fungicide-treated and unsprayed plots was as high as 67% in 1990, 55% in 1991, and 57% in 1992 for the susceptible cultivar IS 18696. The disease had no effect on yield for the moderately resistant cultivar IS 25105 in 1990 and 1991, and caused only 4% loss in 1992. Kernel weight losses were between 18 and 36% for IS 18696 and 15% for IS 25105 in 1991 only.