Inhibitory effect of endophyte bacteria on Botrytis cinerea and its influence to promote the grapevine growth

A grapevine pathogen, Botrytis cinerea, produces characteristic gray mold symptoms on leaves and/or stems within 7 days following the inoculation. In this study we used a plant growth-promoting rhizobacterium, Pseudomonas sp. strain PsJN, which demonstrates an induction of plant growth in parallel with an antagonistic effect on in vitro growth and development of B. cinerea. The simultaneous in vitro co-culture of B. cinerea and bacterium did not stop the spread of fungus. However, when the fungus was introduced 2 days after bacterium inoculation, a clear inhibition of B. cinerea appeared around the zone of Pseudomonas inoculation. When in vitro bacterized plantlets were challenged with B. cinerea, the symptoms of gray mold failed to develop compared to nonbacterized controls. Microscopic observation of B. cinerea mycelium from the zone of contact between the fungus and with Pseudomonas sp. on the potato dextrose agar plate shows a growth disruption of fungal mycelium, coagulation, and leakage of protoplasm. The antagonist had no effect on the polygalacturonase activity of B. cinerea, meaning that the bacterium is not acting directly on the polygalacturonase of the fungus. It seems that the PsJN inhibits the growth of B. cinerea by disrupting cellular membranes and inducing cell death.