INTERSTERILITY GROUPS IN THE PLEUROTUS-OSTREATUS COMPLEX FROM THE CONTINENTAL UNITED-STATES AND ADJACENT CANADA

Mating compatibility studies using strains from 170 North American col lections in the Pleurotus ostreatus complex reveal three intersterile species of oyster mushrooms in the United States and Canada. Initial p airings among monokaryotic single spore isolates were performed to det ermine the number of intersterile groups. Dikaryon-monokaryon pairings using monokaryotic tester strains were then used to screen additional dikaryotic cultures of the oyster mushroom. Pairings of tester strain s from Europe indicate that two European taxa, P. ostreatus and Pleuro tus pulmonarius, are also widely distributed in North America. A third intersterility group occurring primarily on aspen in North America wa s intersterile with all other known species, and is described as a new species, Pleurotus populinus. All three species differ from one anoth er in their morphology, growth characteristics, geographic distributio ns, and host ranges. Other than mating compatibility tests, however, n o single type of character was found to be completely reliable for dis tinguishing these species in the field or under laboratory conditions. Furthermore, morphological characters used to distinguish European sp ecies of the P. ostreatus complex were not useful when applied to corr esponding mating-compatible groups from North America.