Variation in Aggressiveness and Virulence Among Isolates ofCercospora arachidicola

Abstract Forty-three isolates of Cercospora arachidicola, incitant of early leaf spot of peanut, were collected from peanut fields in Florida, Georgia, North Carolina, and Texas. Variation in aggressiveness among these isolates using the susceptible peanut cultivar Spanco was examined in greenhouse tests. Variation (P ≤ 0.05) among the isolates was observed for the parameters of incubation period (IP), the reciprocal of the latent period (an estimate of sporulation rate), and number of lesions per leaflet (LN). Additionally, as a group, the isolates from Texas were more aggressive in terms of having a shorter latent period and greater number of lesions per leaflet than isolates from other states. When a subset of eight isolates, which differed in aggressiveness based on IP and LN, were tested on Spanco and three early leaf spotresistant breeding lines (TX957910–5, TX957910–27, TX957910–68), the breeding lines were resistant to all isolates and, except for lesion diameter, no host genotype-by-isolate inter...