Relationship Between Components of Resistance and Disease Progress of Early Leaf Spot on Virginia-Type Peanut

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Abstract
Early leaf spot (caused by Cercospora arachidicola) was monitored in isolated field plots of 20 Virginia-type peanut (Arachis hypogaea) lines in 1982-1984. Increases in the percentage of diseased leaflets and percent defoliation fit the Gompertz model more closely than the logistic or monomolecular models. Rates of increase in leaf spot incidence and defoliation as well as areas under disease progress curves (AUDPCs) varied among peanut genotypes. Peanut genotypes with larger AUDPCs had faster rates of disease increase. Florigiant, NC 2, and selected lines from crosses of NC 5 .times. Florigiant and crosses of NC 2 .times. NC 5 were more susceptible to early leaf spot than the other entries tested. GP-NC 343 and a selected line from GP-NC 343 .times. NC 5 exhibited the lowest disease levels. Disease levels at 103-110 days after planting contributed most to AUDPCs. AUDPCs were more highly correlated with latent period, percent lesions sporulating, spore production, and time to defoliation than were infection and defoliation rates. The maximum percentage of lesions that sporulated was the resistance component most highly correlated with disease progress in the field.