Influence of Suillus luteus on Fusarium damping-off in pine seedlings

The role of the ectomycorrhizal (Myc) fungus Suillus luteus as a biological control agent against damping off caused by Fusarium verticillioides (Fo) and Fusarium oxysporum (Fm) on Scots (Pinus sylvestris L.) and Stone pine (Pinus pinea L.) was studied in a greenhouse experiment. The vegetative mycelium of S. luteus in a vermiculite/peat carrier was added to potting substrate before inoculation with Fo or Fm spores (macro and microconidia). Also, seedlings were inoculated only with the Myc, Fo, Fm or water for treatment comparisons. The seedling disease index (SDI) of seedlings varied significantly among pine, Fusarium and Myc treatments. Scots pine seedlings inoculated with F. verticillioides and F. oxysporum had a reduced SDI when co-cultured with S. luteus. Damage in Stone pine seedlings inoculated with F. oxysporum was significantly reduced in the presence of Myc fungus, but no reduction of disease symptoms was observed when inoculated with F. verticillioides. Mycorrhizal formation in co-cultures with F. verticillioides was low and absent in co-cultures with F. oxysporum, although S. luteus inoculation resulted in a greater antagonism against this latter pathogen. The protective effect of S. luteus against damping-off by Fusarium species was not related to the percent of mycorrhizal apexes in the roots of Stone and Scots pine seedlings. Key words: Forest nurseries, ectomycorrhiza, Suillus luteus, damping off, Fusarium oxysporum, Fusarium verticillioides, biological control, Pinus species.