Effectiveness of Bacillus subtilis (isolate 25021) in controlling Botrytis cinerea in strawberry

Bacillus subtilis (isolate 25021), originally isolated front mature strawberry fruits, effectively controlled Botrytis cinerea, the causal agent of grey mould in strawberries, in laboratory and field investigations. Germ tube growth of conidia of B. cinerea was strongly inhibited by the culture suspension of the antagonist in aqueous strawberry fruit pulp suspension (1 %), although the germination rate of conidia was not affected. The culture suspension and the washed cells reduced conidiophore density of B. cinerea by 70.7 % and 75.2 %, respectively, on detached strawberry leaf disks. The mode of action of B. subtilis isolate 25021 seems to be based on heat labile substances, since the activity of the culture filtrate was lost after autoclaving. In 3-year field trials (1997-1999), the effectiveness of B. subtilis treatments carried out during bloom to reduce grey mould incidence in fruits was in a range of 16 to 40 % as compared to the water control.