Evaluation of Resistance to Cercospora Leafspot in Peanut Germplasm Potentially Useful in a Breeding Program1

Abstract

Sixteen peanut lines representing diverse germplasm were evaluated in the greenhouse and field for resistance to Cercospora leafspot caused by C. arachidicola Hori. In greenhouse tests, Spantex and Starr developed consistently fewer lesions than NC 3033 and AC 3139 following leaf inoculation with C. arachidicola. In field evaluations, with naturally occurring inoculum, the reverse was true. Defoliation of the lines was compared in chlorothalonil sprayed and nonsprayed field plots. ‘NC 3033’, ‘NC 5’ and ‘AC 3139’ were more resistant to defoliation than ‘Starr’, ‘Tennessee Red’, ‘Spantex’, ‘Argentine’ and ‘Spancross’. Spancross had an intermediate number of lesions at all sample dates but had the highest defoliation. Plants grown continuously in the greenhouse tended to develop more lesions than did plants grown outside for 2 weeks before inoculation. The reduction in lesion number was most striking on NC 3033.A disease index indicative of the interaction between number of lesions per leaf and precent defoliation showed that NC 3033, NC 5 and AC 3139 were more resistant than Spantex, Argentine, Starr and Tennessee Red in field tests. The defoliation ratio technique was very reliable in field tests and had less variability than counting number of lesions or lesion size. Visual estimation of percent leaves infected, however, was a rapid, efficient method for evaluation when large number of plants per entry are available. Entries most useful as parents in breeding for resistance to Cercospora leafspot are NC 3033, NC 5, and AC 3139.