Bioassay methods for the detection of antifungal activity by Pseudomonas antimicrobica against the grey mould pathogen Botrytis cinerea

Antagonism against the grey mould pathogen Botrytis cinerea by Pseudomonas antimicrobica was demonstrated in vitro and in vivo. Cell-free filtrates showed activity against B. cinerea growing on Potato Dextrose Agar (PDA) in a media-dependent manner with the most distinct antagonism being produced in Czapek Dox Broth (CDB). Cell-free filtrates of CDB-grown cultures also significantly reduced conidial germination of B. cinerea. An assays based on the inhibition of conidial germination was compared with two assays measuring the antagonism of mycelial growth on PDA. The conidial germination bioassay was more sensitive in the detection of this antifungal activity than the Petri dish bioassay while a bioassay using Microdetection plates did not detect antagonism due to the small loading capacity of the latter. The conidial germination bioassay was modified for detection of antibiosis on the surface of strawberry leaves. Significant reductions in percentage conidial germination were recorded on the surface of leaves of both micropropagated and glasshouse grown strawberry plants when the antifungal compounds of Ps. antimicrobica were applied to the leaf tissue with the conidia. In addition, antifungal compounds were also detectable when conidia were applied to leaf tissue which had previously been sprayed with cells of Ps. antimicrobica. These tests indicate that Ps. antimicrobica would be a suitable biocontrol agent for the control of B. cinerea.