Selective isolation of bacterial antagonists of Botrytis cinerea

Most potential fungal antagonists have been identified only after exhaustiv e non-selective screening. Bacteria antagonistic to Botrytis cinerea were s elected using a simple method based on techniques developed for trace enric hment studies, where a crude cell wall preparation from B. cinerea was used as a selective substrate and bacteria were isolated based on growth on cel l wall agar media. Most of the 52 bacterial isolates that were obtained fro m the surface of 'organically grown' strawberry fruit and could grow on B. cinerea wall media in culture showed some ability to inhibit the growth of the fungus. Potato dextrose agar seeded with B. cinerea spores (10(4) ml(-1 )) were challenged with each of these bacterial isolates at concentrations of 10(9) and 10(6) colony forming units ml(-1). Eleven of the 52 isolates i nitially recovered, subsequently demonstrated strong antagonism in vitro an d were selected for additional screening tests on strawberry fruit. All 11 isolates reduced grey mold rot incidence on fruit in storage. Three of the best isolates were tested in limited held trials, and also reduced grey mol d rot on fruit under field conditions.