F Waliyar; BB Shew; HT Stalker; TG Isleib; R Sidahmed; MK Beute
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Abstract: Expression of resistance to early leaf spot disease of peanut, caused by Cercospom arachidicola, varies across diverse geographic locations. Environment is known to influence expression of partial resistance in some pathosystems and could affect stability of resistance to eariy leaf spot. Multiple components of resistance were studied at controHed temperatures on seven peanut genotypes selected at North Carolina State University and on six genotypes selected at ICRISAT in West Africa. The genotypes were inoculated with a North Carolina field isolate of C. arachidicala and incubated underdaylnight temperature regimes of 24/24, 26/20, 32/26, 38/26, and 38/32 C (the high-temperature regimes simuEate the conditions in Niger, West Africa, and the cooier regIrnes simulate the conditions in North Carolina). Numbers of Lesions were inversely related to temperature. Days after inoculation significantly influenced numbers of lesions and infection frequency. Regression of lesion numbers ar infection frequencies on time and temperature accounted for 90% or more of experimental variation for 12 of 13 genotypes. Values far most resistance ~&~onentesx amined (number of lesion;; infection frequency, incubation period. lesion diameter. and necrotic area diameter) were dependent on both temperature and genotype. Several peanut genotypes wcre identified that expressed stable levels of resistance to C. oruchidicola across temperature regimes. The North Carolina line 91 PA 150, derived from the wild diploid species Arachis cardenusii, consistently was ranked as resistant for all components in all temperature regimes. Other genotypes that ranked high in partial resistance ta C. orochidicola included NC Ac 17894, PI 274394, NC Ac 18045, and 91 PA 131. Another group of genotypes, includ~ng GP-NC 343, NC 6, and N92069L, were moderately reststant. PI 476033 and NC 7 were highly susceptible at all temperatures, and N92064L varied in ranking for components.