Bioassays on Leptographium wingfieldii, a bark beetle associated fungus, with phenolic compounds of Scots pine phloem

The fungicidal activity of five phenolic metabolites occurring in Scots pin e phloem (Cat, Tax, PS, PC and PSM) and of phenolic extracts from unwounded (fresh) and wounded phloem of Scots pine were measured against Leptographi um wingfieldii, a fungus associated with Tomicus piniperda. Bioassays were performed in micro-wells in a standard medium in the absence and presence o f Scots pine phloem. In both media, methanol extracts from the unwounded an d wounded phloem, PS, PSM and PC inhibited fungal growth. Tax and Cat had n o effect or stimulated fungal growth. The presence of Scots pine phloem in the liquid medium reduced the inhibitory effect of phenolic compounds. At l ow concentrations (10(-4)-10(-5) M), the fungus seemed to be able to degrad e PS, PSM and PC while, whatever the Cat and Tax concentrations, it did not seem to degrade them. These results suggest that three phenolic compounds have a potential fungitoxicity in vitro and that, in vivo, these phenols co uld play a role in the efficiency of the induced reaction to stop fungal gr owth.