INTERSTERILITY GROUPS IN COLLYBIA-SUBNUDA

Two intersterility groups occur within Collybia subnuda. The two inter sterility groups retain a low level of intercompatibility in vitro. Th ey are similar morphologically and have nearly identical intergenic tr anscribed spacer rDNA sequences. Intersterility group 1 is usually fou nd on oak leaf litter, while intersterility group 2 is usually found a ssociated with oak wood. Collection records and the results of interco llection pairing among single-spore isolates indicate that the two int ersterility groups are sympatric throughout the Appalachian Mountains and into New York. Both intersterility groups produce binucleate basid iospores in low frequency, and thus have the potential for secondary h omothallism. A mechanism for sympatric evolution of heterothallic Basi diomycetes is proposed, but neither a sympatric nor allopatric origin for the C. subnuda ISGs is advocated.