Ectomycorrhizal formation and plantation performance of Douglas-fir nursery stock inoculated with Rhizopogon spores

Abstract

Basidiospores of seven species of hypogeous, ectomycorrhizal fungi were inoculated on four conifer species in a bare-root nursery. Inoculation with either Rhizopogonvinicolor Smith or Rhizopogoncolossus Smith succeeded with two provenances of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). For R. vinicolor, the high spore-application rate produced the most mycorrhizae on the greatest number of seedlings. For R. colossus, the high spore-application rate produced the most mycorrhizae on the greatest number of seedlings of seed source 062, whereas the medium rate did better with seed source 252. Stem height and root collar diameter of seedling did not differ significantly between treatments and controls. Douglas-fir seedlings inoculated or not inoculated with spores of R. vinicolor were outplanted in southwestern Oregon. After 2 years, inoculated seedlings had significantly greater survival, stem height, root collar diameter, and biomass than noninoculated seedlings. Although new feeder roots of both noninoculated and inoculated seedlings were colonized by indigenous fungi, R. vinicolor persisted on the old root systems of inoculated seedlings and colonized new feeder roots.