LATE LEAF-SPOT PROGRESSION ON PEANUT AS AFFECTED BY COMPONENTS OF PARTIAL RESISTANCE

Components of partial resistance to late leaf spot (Cercosporidium personatum) and disease progression on 14 peanut genotypes were quantified in field experiments at Marianna, Florida, during 1988 and 1989. The resistance components measured were 1) incubation period, 2) latent period, 3) maximum percentage of lesions that sporulated, 4) lesion size, 5) lesion number, 7) degree of sporulation, and 7) percent necrotic area. Lower area under the disease progress curve (AUDPC) values, reduced apparent infection rates, and lower end-of-season disease levels were observed on genotypes UF81206-1, PI 261893, US29-b3-B, and US202-b2 compared to other genotypes in the study. Both apparent infection rate and AUDPC values were highly correlated with latent period (r = -0.68 to -0.79, P less than or equal to 0.01) and maximum percentage of lesions that sporulated (r = 0.72-0.81, P less than or equal to 0.01). Latent period and maximum percentage of lesions that sporulated were the components most highly correlated with late leaf spot disease development, and these two components were highly correlated with one another (r = -0.84). Using either of these two components to evaluate peanut genotypes for resistance to late leaf spot may facilitate more rapid selection of lines with improved levels of rate-reducing resistance.