Biological control of Botrytis cinerea Pers. ex. Fr. in strawberry by Paenibacillus polymyxa (isolate 18191)

Isolate 18191, obtained from mature strawberry fruit and determined as Paen ibacillus polymyxa has shown an antagonistic potential against Botrytis cin erea, the causal agent of grey mould in strawberries. Germ tube growth of c onidia of B. cinerea was strongly inhibited by the culture suspension of th e antagonist in aqueous strawberry fruit pulp suspension (1%) but germinati on rate of conidia was not affected.. The application of the culture suspen sion and the washed cells on detached strawberry leaf discs reduced conidio phore density of B. cinerea by 67 and 84%, respectively. The treatment of d etached lear discs with culture suspensions of different cell densities (1 x 10(6), 1 x 10(7), 1 x 10(8)) showed that the lowest density already reduc ed incidence of B. cinerea by 68% after 8 days incubation period. Investiga ting the influence of the temperature on the effectiveness of P. polymyxa i t was observed that the antagonist was highly effective already at 10 degre esC and reduced incidence and conidiophore density of B. cinerea by 53 and 58%, respectively. In 3-year field trials the effectiveness of P. polymyxa was in a range of 24-36% as compared to the water control.