VIEW ARTICLE

Resistance

Components of Partial Resistance in Peanut Genotypes to Isolates of Cercosporidium personatum from the United States and Thailand. B. B. Shew, Research associate, Department of Crop Science, North Carolina State University, Raleigh 27695-7616; T. Sommartya, and M. K. Beute. (2)Visiting assistant professor, Department of Plant Pathology, North Carolina State University, Raleigh, and plant pathologist, Kasetsart University, Bangkok, Thailand; (3)Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 79:136-142. Accepted for publication 1 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-136.

Leaves were detached from 14 peanut (Arachis hypogaea) genotypes that previously were characterized as having low, moderate, or high partial resistance to Cercosporidium personatum. Detached leaf cultures were inoculated with isolates of C. personatum from diverse locations within Thailand and the United States. Lesion numbers, the percentages of lesions that sporulated 20 (%LS20) and 30 (%LS30) days after inoculation, lesion diameters, and conidial production per sporulating lesion were determined. Thai isolates of C. personatum generally caused more lesions than U.S. isolates on all genotypes. Differences among isolates for other disease components were small and varied between two trials. Stability of resistance to several disease components was evaluated with regression analysis, in which low mean disease ratings, nonsignificant deviations, and slopes near zero in the regression indicated stable resistance. Significant slopes, which indicate increasing disease with increasing isolate virulence, occurred in lesion numbers, %LS20, %LS30, and conidial production for some genotypes. Few significant deviations, which indicate significantly higher disease in specific isolate x genotype combinations, were found among moderately and highly resistant genotypes. The three most resistant genotypes varied little in overall resistance but differed in stability of resistance. KUP 24D-248W, a genotype selected in Thailand, had the most stable resistance to the isolates tested. Differences within isolates and between trials were nearly as great as differences among isolates from the diverse locations.