Biology of the ectomycorrhizal genus, Rhizopogon

Abstract

SliMMARYSeedlings of Abies grandis, Alnus rubra, Pinus ponderosa, Picea sitchensis, Pseudotsuga menziesii and Tsuga heterophylla were grown in monoculture and dual culture in the greenhouse and inoculated with spore slurries of 20 isolates representing 15 species of ectomycorrhizal hypogeous fungi {11 Rhizopogon species, Alpoz'a diplophloeus, Truncocolumella citrina, Melanogaster euryspermus and Zetleromyces gilkeyae). The primary objectives were to assess and compare the pattern of bost specificity between symbionts and to study the influence of neighbouring plants on ectomycorrhiza development. None of the fungai species had broad host range affinities. A variety of specificity responses were exhibited by the different fungal taxa, rangmg from genus-restricted to intermediate host range. In monoculture, nine species oi Rhizopogon (R. arctostaphyli, R. ellenae, R. flavofibrillosus, R. occidentalis, R. rubescens, R. smithii, R. suhcaerulescens, R. truncatus and R. vulgaris) formed ectomycorrhizas on Pinu.'! ponderosa whevess three Rhizopogon species {R. parksii, R. vinicolor and R. suhcaerulescens) formed ectomycorrbizas on Pseudotsuga menziesii. Truncocolumella citrina associated with Pseudotsuga menziesii and Alpozia diplophloeus with Alnus ruhra. Melanogaster euryspermus and Z. gilkeyae did not form ectomycorrhizas with any hosts. None of the fungi tested developed ectomycorrhizas on Ahies grandis, Tsuga heterophylla or Picea sitchensis in monoculture. In dual culture, the same nine Rhizopogon species that formed abundant ectomycorrhizas on Pinus ponderosa formed some ectomycorrhizas on secondary hosts such as Ahies grandis., Tsuga heterophylla, Pseudotsuga menziesii and Picea sitchensis. Similarly, Truncocolumella citrina formed abundant ectomycorrhizas on Pseudotsuga menziesii and low levels on the secondary hosts Abies grandis, Tsuga heterophylla and Picea sitchensis. Rhizopogon parksii and R. vinicolor only formed ectomycorrhizas on Pseudotsuga menziesii, and Alpova diplophloeus only formed ectomycorrhizas on Alnus rubra. The specificity pattern obtained by using this dual-culture approach is contrasted with previous pure-culture synthesis data and is discussed in terms of potential interplant linkages and community dynamics.

Biology of the ectomycorrhizal fungal genus, Rhizopogon

“…These patterns were confirmed in a large scale spore inoculation test involving 13 Rhizopogon H. B. 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 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). Several section Villosuli species also co-occur with Pseudotsuga menziesii in exotic plantations in Europe (Gross et al, 1980 ;Jansen & de Vries, 1989 ;Parlade!…”

“…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). An exception is the thorough description of Rhizopogon luteolusjPinus sylvestris by Uhl (1988) and Rhizopogon subcaerulescensjTsuga heterophylla by Agerer et al (1996).…”

“…As a compromise between artificial axenic and natural field conditions, Massicotte et al (1994) used spore inoculation to synthesize Rhizopogon ectomycorrhizas on glasshouse seedlings reared in a peat moss and vermiculite substrate which provided a well aerated substrate with seedling tops exposed to an open air environment, and included the presence of other soil microbes. This synthesis approach produced abundant ectomycorrhizal roots which were easily extracted and cleaned for sectioning and microscopic examination.…”

“…This synthesis approach produced abundant ectomycorrhizal roots which were easily extracted and cleaned for sectioning and microscopic examination. The current study uses ectomycorrhizas synthesized by Massicotte et al (1994) for two objectives : to provide detailed anatomical descriptions of different Rhizopogon species on Ponderosa pine using light and scanning electron microscopy (SEM) ; to compare isolates from the different Rhizopogon sections for anatomical similarities of the ectomycorrhizas formed. It was not the aim of this study to provide detailed descriptions that could be used in identifying morphotypes in field-collected samples.…”