Accumulation of compatible solutes in Penicillium frequentans grown at reduced water activity and biocontrol of Monilinia laxa

The biocontrol fungus Penicillium frequentans was grown on potato dextrose broth of either - 0.4 MPa water potential (unstressed) or reduced water pot ential (stressed) media modified with glycerol to -7.0 MPa. The endogenous compatible solutes and sugars were quantified after 5, 10 and 15 days growt h. Glycerol was the main compatible solute accumulated at reduced water pot ential, with a concomitant decrease in erythritol and mannitol, and the sug ar; glucose. Maximum accumulation of glycerol occurred in 5-day-old culture s, with the content in P. frequentans biomass produced at reduced water pot ential being about 180 times higher than that produced in unmodified medium (-0.4 MPa). There It as no enhanced accumulation of the desiccation protec tant trehalose. Homogenisation of cultures, for spray applications of the f ungus, resulted in a partial loss of the solutes accumulated in the fungal biomass. P. frequentans controlled peach brown rot (Monilinia laxa) on peac h twigs, with the disease index being significantly smaller when treated wi th the antagonist produced at reduced water potential. However both inoculu m types were able to reduce the length of lesions to a similar extent. This suggests that the inoculum of the antagonist produced in medium with freel y available water (-0.4 MPa) becomes rapidly adapted to the dry environment in the phyllosphere counteracting the possible initial advantage of the in oculum produced at reduced water potential ( - 7.0 MPa).