Rutin, the phenolglycoside from eucalyptus root exudates, stimulates Pisolithus hyphal growth at picomolar concentration

Ectomycorrhizal hyphal growth is shown to be stimulated by a phenol compoun d isolated from Eucalyptus globulus ssp. bicostata root exudates, highlight ing the importance of phenolics in host-fungal interaction. HPLC analysis allowed separation and identification of phenolic compounds f rom Eucalyptus seedling tissues and root exudates. The activity of the flav onol, rutin, was tested on a range of mycorrhizal and saprophytic fungi. Rutin stimulated Pisolithus hyphal growth by more than twofold, and the fun gus responded significantly to concentrations as low as 1 pM; only a few st rains responded. Rutin from Eucalyptus globulus ssp. bicostata root exudates is a flavonoid signal for Pisolithus, and is the first such flavonoid signal identified. A rutin gradient could contribute to orientating hyphal elongation toward th e root tip thereby favouring mycorrhizal infection, and might also influenc e the interaction between fungi in the rhizosphere.