Improvement of basidiospore germination and mycelial growth of the ectomycorrhizal mushroom Rhizopogon roseolus in axenic conditions

Abstract

Rhizopogon roseolus (Corda) Th. Fr. is an economically important edible mycorrhizal mushroom. We previously developed techniques for artificial cultivation of this mushroom using mycorrhizal pine seedlings, but stable production of fruiting bodies has not been accomplished. Selection of superior strains by crossbreeding is a promising approach to increase the yield of fruiting bodies, which requires genetically diverse homokaryons. To obtain abundant homokaryons from basidiospores, we evaluated the relationship between composition of the agar medium and germination rate of basidiospores as well as vegetative hyphal growth. Five agar medium compositions were prepared as a base for MMN medium. A higher germination rate was observed on diluted MMN medium than on full-strength MMN medium. Additionally, larger colony diameters were observed on diluted MMN medium than on MMN medium. These results implied that the optimum medium for basidiospore germination positively correlated with the optimum medium for vegetative hyphal growth on axenic agar. Among the tested media, 1/5 diluted MMN agar medium was optimum for basidiospore germination and subsequent mycelial colonization of homokaryotic hyphae, showing that this medium was useful for obtaining abundant homokaryons in R. roseolus.