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Different Ratios of General:Specific Virulence Variance Among Isolates of Cylindrocladium crotalariae from Different Peanut Genotypes. M. C. Black, Former research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650, Present address: Texas A&M University Agricultural Research and Extension Center, Uvalde 78801; M. K. Beute, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 74:941-945. Accepted for publication 8 March 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-941.

One hundred and forty-five isolates of Cylindrocladium crotalariae were obtained from seedlings of six peanut (Arachis hypogaea) genotypes grown in peanut-field soil. Resistant peanut cultivar NC 3033 and susceptible cultivar Florigiant were used as host differentials to compare isolate variability for virulence. There was a trend for general virulence for Cylindrocladium black rot to differ among groups of isolates from different genotypes. The overall root rot mean was highest for isolates from resistant NC 3033 and lowest for isolates from susceptible NC 6. Isolates obtained from resistant genotypes NC 3033 and NC 18231 had high variance for virulence specific to host differentials. Isolates from NC 3033 and NC 18231 had low and intermediate ratios of general:specific virulence variance, and these ratios were the two lowest among the six sources of isolates compared.