Antifungal activity of the volatile compound isovelleral produced by ectomycorrhizal Russula fungi against plant-pathogenic fungi

Fruiting bodies of ectomycorrhizal fungi were collected from different areas of Tottori Prefecture, Japan, during 2011-2015, and 18 species were identified by morphological characteristics and molecular analysis. Volatile compounds were extracted with acetone from fruiting bodies, and after concentration, the aqueous residue was extracted with n-hexane. The antifungal activities of the volatile extracts were assayed by inhibition of conidial germination of a phytopathogenic fungus, Alternaria brassicicola; the volatiles from Russula aff. anthracina, R. chloroides and R. senecis completely inhibited conidial at 1 ppm (w/v), the maximum concentration diffused as vapor. In addition, volatile compounds from R. aff. anthracina had remarkable antifungal activity against seven phytopathogenic fungi when tested at vapor concentrations of 0.2 ppm (w/v). The conidia of A. brassicicola did not germinate even after the removal of the volatile compounds, indicating that the active compound had fungicidal activity. The volatile compounds were isolated from the extracts of R. aff. anthracina, and isovelleral was identified as the major antifungal compound. Isovelleral was also detected in the extracts of R. chloroides and R. senecis and had significant antifungal activity against conidial germination of A. brassicicola at a vapor concentration as low as 0.05 ppm (w/v). This is the first report that isovelleral, the volatile compound produced by Russula spp., has antifungal activity against phytopathogenic fungi.