EFFECT OF TEMPERATURE ON STABILITY OF COMPONENTS OF RESISTANCE TO CERCOSPORA-ARCHIDICOLA IN PEANUT

Expression of resistance to early leaf spot disease of peanut, caused by Cercospora arachidicola, varies across diverse geographic locations . Environment is known to influence expression of partial resistance i n some pathosystems and could affect stability of resistance to early leaf spot. Multiple components of resistance were studied at controlle d temperture on seven peanut genotypes selected at North Carolina Stat e University and on six genotypes selected at ICRISAT in West Africa. The genotypes were inoculated with a North Carolina field isolate of C . arachidicola and incubated under day/night temperature regimes of 24 /24, 26/20, 32/26, 38/26, and 38/32 C (the high-temperature regimes si mulate the conditions in Niger, West Africa, and the cooler regimes si mulate the conditions in North Carolina). Numbers of lesions were inve rsely related to temperature. Days after inoculation significantly inf luenced numbers of lesions and infection frequency. Regression of lesi on numbers or infection frequencies on time and temperature accounted for 90% or more of experimental variation for 12 of 13 genotypes. Valu es for most resistance components examined (number of lesions, infecti on frequency, incubation period, lesion diameter, and necrotic area di ameter) were dependent on both temperature and genotype. Several peanu t genotypes were identified that expressed stable levels of resistance to C. arachidicola across temperature regimes. The North Carolina lin e 91 PA 150, derived from the wild diploid species Arachis cardenasii, consistently was ranked as resistant for all components in all temper ature regimes. Other genotypes that ranked high in partial resistance to C. arachidicola included NC Ac 17894, PI 274194, NC Ac 18045, and 9 1 PA 131. Another group of genotypes, including GP-NC 343, NC 6, and N 92069L, were moderately resistant. PI 476033 and NC 7 were highly susc eptible at all temperatures, and N92064L varied in ranking for compone nts.