Variability Among Isolates of Rhizoctonia solani Associated with Snap Bean Hypocotyls and Soils in New York. J. J. Galindo, Graduate Research Assistant, Department of Plant Pathology, Cornell University, Geneva, NY 14456. G. S. Abawi, Associate Professor, Department of Plant Pathology, Cornell University, Geneva, NY 14456, and H. D. Thurston, Professor, Department of Plant Pathology, Cornell University, Ithaca 14853. Plant Dis. 66:390-394. Accepted for publication 26 June 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-390.

Thirty-three isolates of Rhizoctonia solani associated with snap bean hypocotyls and soils in New York and six isolates from bean leaves in Colombia, South America, varied considerably in their growth rate, sclerotia production, color of vegetative hyphae, and zonation in culture. Positive association was found between the virulence of the isolates to beans and their growth rate. Disease severity generally was greater at higher soil moisture and higher relative humidity. R. solani isolates from New York varied from weakly to highly virulent on hypocotyls. Several isolates incited damping-off, but most isolates caused only reduction in plant growth. Isolates with fast to intermediate growth rates were also able to cause leaf infection. All the isolates from Columbia were highly virulent in both hypocotyls and leaves. Virulence in bean hypocotyls and leaves differed widely among anastomosis groupings (AG) but not within each group. Eighteen of the 33 isolates of R. solani associated with bean hypocotyls and soils in New York were in AG-4, four in AG-1, five in AG-2, and none in AG-3. All six isolates from Colombia were in AG-1.

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