Effects of bacterial strains isolated from the ectomycorrhizal roots of Laccaria parva on sporocarp production by the fungus in vitro

Abstract

Abstract The effects of bacteria isolated from ectomycorrhizas on sporocarp production of Laccaria parva were examined in vitro. Three bacterial strains of Bradyrhizobium were selected on the basis of their affinity for L. parva LL02 in previous confrontation tests: a positive or a negative strain that significantly increased or decreased hyphal extension areas, and a neutral strain that did not have significant effects on them. Mycelia of LL02 and a suspension of each bacterial strain were inoculated onto a surface-sterilized pine seedling in a glass bottle and then incubated for 3 mo in an illuminated incubator. Plant biomass did not differ significantly among the treatments, but the level of ectomycorrhizal colonization was low in the treatment inoculated with a negative strain (Neg treatment). The frequency with which mature sporocarps occurred was higher in treatments inoculated with positive (Pos treatment) or neutral strains (Neu treatment) compared with control and Neg treatments. The ratio of biomass accounted for by mature sporocarps was low in control and Neg treatments, and high in Pos and Neu treatments. These results indicate that bacteria colonizing ectomycorrhizas affect the production of sporocarps and that the affinity between fungi and bacteria is likely to underlie this interaction.