Characterization of Rhizoctonia spp. isolates collected from Phaseolus vulgaris in Puerto Rico

Thirteen isolates collected from soil samples, infected seeds, hypocotyls, leaves and pods of common beans (Phaseolus vulgaris) grown in the northwestern, southern and western areas of Puerto Rico were identified as Rhizoctonia solani (Rs), and one as binucleate Rhizoctonia sp. (Rb). All isolates were characterized by the nuclear condition of the hyphae cell and the anastomosis technique. Seven Rs isolates (54%) were classified into anastomosis group AG 4, and six (46%) were assigned to AG 1. The microsclerotic Rb isolate did not anastomose with any of the AG testers. The AG 4 isolates produced only microsclerotia. Five AG 1 isolates (36%) were macrosclerotic, and one was microsclerotic. The Rs isolates and the Rb isolate differed in mycelia radial growth after 48 h of incubation at 28 degrees C on acidified potato dextrose agar. The sexual stage of the isolates was not observed throughout this research. Storing dried beet (Beta vulgaris L.) seeds colonized by R. solani for at least a year at 4 degrees C in the dark seems to be a reliable method to ensure viability and virulence of the pathogen.