BIOLOGY OF THE ECTOMYCORRHIZAL GENUS, RHIZOPOGON .1. HOST ASSOCIATIONS, HOST-SPECIFICITY AND PURE CULTURE SYNTHESES

Twenty nine isolates of Rhizopogon from 20 spp. differed markedly in t heir ability to form ectomycorrhizas with Douglas fir, western hemlock and lodgepole pine in pure-culture syntheses. Within the four section s of Rhizopogon there were similarities in ectomycorrhizal appearance and range of potential hosts. Intermediate and overlapping ectomycorrh izal characters were evident in closely related species complexes. Alt hough the host-specificity of many species, based on field observation s of sporocarps, often correlated with their host range in the synthes es, some fungi formed well-developed ectomycorrhiza on hosts with whic h they appear not to be associated in the field. The specificity of ho st associations is suggested as a major contributor to the speciation and diversification of Rhizopogon in the Pacific Northwest of the USA and Canada.