VIEW ARTICLE

Resistance

Variability of Cylindrocladium crotalariae Response to Resistant Host Plant Selection Pressure in Peanut. B. A. Hadley, Former graduate student, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture (USDA), Department of Plant Pathology, North Carolina State University, Raleigh, 27650, Present address of senior author: Biochemicals Department, Experimental Station, E. I. du Pont de Nemours and Co., Inc., Wilmington, DE 19898; M. K. Beute(2), and K. J. Leonard(3). (2)(3)Professor, and plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture (USDA), respectively, Department of Plant Pathology, North Carolina State University, Raleigh, 27650. Phytopathology 69:1112-1114. Accepted for publication 16 April 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1112.

Seventy-nine isolates of Cylindrocladium crotalariae originally obtained from plants of the resistant peanut cultivar NC 3033 and 11 isolates obtained from susceptible plant species including peanut were tested by inoculating replicates of the susceptible cultivar Florigiant and resistant cultivar NC 3033. The mean virulences of isolates from the susceptible hosts did not differ significantly from those of isolates from the resistant host. When disease data were fitted to a pathogen virulence model, however, differences were noted among isolates from the resistant host. As isolates became adapted to NC 3033, they tended to become less adapted to Florigiant. Following only one cropping cycle of the resistant host, virulence specific for NC 3033 increased in a previously nonselected pathogen population. The results indicate that a potential exists for race development in C. crotalariae even though corresponding resistance in the host appeared to be quantitatively inherited.