Secondary metabolites and extracellular proteases contribute to the antagonistic action of indigenous Trichoderma strains against Botrytis cinerea.

The aim of this work is to evaluate different molecular strategies deployed by indigenous isolates of Trichoderma in their interaction with the phytopathogen Botrytis cinerea. In vitro antagonism assays, determination of volatile and diffusible compounds, and the relative expression of the prb1 gene, which codes for an extracellular protease, before and during the stage of direct contact between the two fungi, were carried out; the characterization of this protease was also performed. All 17 Trichoderma strains tested showed high levels of inhibition against B. cinerea growth in dual culture, with overgrowth of antagonist colonies on top of pathogen colonies being observed in most cases. Pathogen growth inhibition by antagonist-released volatile compounds ranged from 17 to 100 %, while the inhibition linked to the production of diffusible compounds ranged from 13 to 100 %. The prb1 gene was shown to be three-fold upregulates compared to growth alone before direct contact between the two fungi was established and then its transcript levels declined again at the direct contact stage. In the Trichoderma culture supernatant, the presence of elastase-type serine proteases (SP) associated with the initiation of the mycoparasitism process could be observed.