BACTERIA ASSOCIATED WITH SUILLUS-GREVILLEI SPOROCARPS AND ECTOMYCORRHIZAE AND THEIR EFFECTS ON IN-VITRO GROWTH OF THE MYCOBIONT

Twenty seven bacterial species were isolated from both the sporocarps of Suillus grevillei and the ectomycorrhizae of Suillus grevillei-Lari x decidua. The genera Pseudomonas, Bacillus and Streptomyces were pred ominant. Several species were common to both the sporocarps and the ec tomycorrhizae. Dual culture trials between Gram-positive, Gram-negativ e, Streptomyces and five different isolates of S. grevillei showed sev eral behavior patterns depending on the bacterial group, the fungal is olate and the time. Gram-positive bacteria seldom stimulated fungal gr owth. Among Gram-negative bacteria, Pseudomonas fluorescens strain 70 and Pseudomonas putida strain 42 showed the greatest enhancement of gr owth. Streptomyces always caused significant inhibition of the fungus: Bacterial supernatants never significantly stimulated fungal growth; volatile metabolites frequently enhanced fungal growth but seldom sign ificantly. Most of the bacterial isolates produced siderophores. The r esults obtained suggest for some bacterial strains a very high fungus selectivity at the intraspecific level.