In vitro and in vivo screening of antagonistic bacterial strains from vineyards to controlBotrytis cinereain grapevine tissues

Botrytis bunch rot, caused by Botrytis cinerea, is an important fungal disease of grapevine with high economic importance in wine grape production and postharvest storage of table grapes. Biological control by antagonistic bacteria is a promising strategy for reducing the common use of synthetic fungicides to control this pathogen. A total of 45 bacterial strains, isolated from grapevine tissues in 'Bordeaux' vineyards were screened in vitro for their potential antifungal activity against two major vineyard subpopulations of B. cinerea, i.e., transposa and vacuma. These two transposon genotypes differ significantly in virulence on grape berries. The inhibitory effects of the bacterial strains on the mycelial growth were tested in vitro for detecting the potential production of diffusible metabolites and volatile organic compounds. Furthermore, ten strains among the most effective ones were selected and evaluated in vivo on detached grapevine host organs: leaf discs and grape berries. We showed that some of the bacterial strains strongly inhibited B. cinerea mycelial growth under in vitro conditions, and also significantly reduced rot severity in vivo. The results suggest the potential to control postharvest gray mold by some of the bacterial strains tested.