Biology of the ectomycorrhizal genus, Rhizopogon

Abstract

SUMMARY Twenty nine isolates of Rhizopogon from 20 spp. differed markedly in their ability to form ectomycorrhizas with Douglas fir, western hemlock and lodgepole pine in pure‐culture syntheses, Within the four sections of Rhizopogon there were similarities in ectomycorrhizal appearance and range of potential hosts. Intermediate and overlapping ectomycorrhiza! characters were evident in closely related species complexes. Although the host‐specificity of many species, based on field observations of sporocarps, often correlated with their host range in the syntheses, some fungi formed well‐developed ectomycorrhiza on hosts with which they appear not to be associated in the field. The specificity of host associations is suggested as a major contributor to the speciation and diversification of Rhtzopogon in the Pacific Northwest of the USA and Canada.

Biology of the ectomycorrhizal fungal genus, Rhizopogon

“…Smith (1964) erected four sections (Villosuli, Fulviglebae, Amylopogon, and Rhizopogon) based on macro-and microscopic features and chemical testing. Molina & Trappe (1994) found a strong correlation between these sections and host specificity in a comprehensive ectomycorrhizal pure culture synthesis experiment with 29 isolates representing 20 species of Rhizopogon on three conifer species (Pseudotsuga menziesii, Tsuga heterophylla, and Pinus contorta). Section Villosuli was almost exclusively ectomycorrhizal with Pseudotsuga, section Rhizopogon affiliated strongly with Pinus, and sections Fulviglebae and Amylopogon were intermediate and able to form ectomycorrhizas with several genera in Pinaceae.…”

“…Several field studies and seedling bioassays have shown the widespread prevalence and ecological importance of Rhizopogon (Molina & Trappe, 1994). In Pacific Northwest forests dominated by Pseudotsuga menziesii (Douglas fir), several section Villosuli species occur on seedlings as well as on young and ancient trees (Trappe, 1965 ;Zak, 1971 ;Alvarez & Linderman, 1983 ;Castellano, 1987 ;Borchers & Perry, 1990 ;Massicotte et al, 1992Massicotte et al, , 1994Miller et al, 1992 ;Smith et al, 1995).…”

“…Massicotte et al species and five genera (Massicotte et al, 1994). Constant associations of Rhizopogon sporocarps with specific conifer genera also bear out this pattern of host specificity in natural and exotic forests worldwide (Molina & Trappe, 1994).…”

“…In past studies, ectomycorrhizas have been synthesized between several Pinus species and different Rhizopogon species (see Molina & Trappe, 1994, for a complete listing) ; R. luteolus, R. roseolus and R. rubescens have received the most attention. In most of these studies, however, the morphological and anatomical descriptions of RhizopogonjPinus are general in nature, and focus on mantle colours, textures and layering, and the presence and extent of Hartig net development (Modess, 1941 ;Bjo$ rkman, 1947 ;Fontana & Centrella, 1967 ;Pachlewski & Pachlewska, 1968, 1974Froidevaux & Amiet, 1975 ;Molina & Trappe, 1982Massicotte et al, 1994 ;Molina et al, 1997).…”

“…The greatest assemblage of species occurs in western North America, particularly in the Pacific Northwest where Pinaceae species serve as ectomycorrhizal hosts. Indeed, the diversity of hosts and forest habitats in this region is likely to have contributed significantly to the speciation of Rhizopogon (Smith & Zeller, 1966 ;Molina & Trappe, 1994).…”