Variability Among Isolates ofRhizoctonia solaniAssociated with Snap Bean Hypocotyls and Soils in New York

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Abstract
Thirty-three isolates of R. solani associated with snap bean hypocotyls and soils in New York and 6 isolates from bean leaves in Colombia, South America, varied considerably in their growth rate, sclerotial 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 Colombia 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. sonai associated with bean hypocotyls and soils in New York were in AG-4, 4 in AG-1, 5 in AG-2, and none in AG-3. All 6 isolates from Colombia were in AG-1.