Comparative analysis of vineyard-associated bacteria and their antagonistic activity against Botrytis cinerea

Aim To isolate bacteria from grapevine leaves and vineyard soil and evaluate their putative modes of action against the fungus Botrytis cinerea which causes grape bunch rot. Methods and Results In this study, we isolated 188 bacteria from soil and leaves, collected from two vineyards in Stellenbosch. Dual culture assays were used to screen the isolates against three Botrytis cinerea strains. Nine isolates (8 Bacillus species and 1 Pantoea agglomerans) with ≥60% antifungal activity against the three B. cinerea strains were identified and further characterized. The antifungal activity declined at low pH with only 6 of the isolates displaying antifungal activity at pH 5. All strains produced chitinase while only five produced glucanase as part of their antifungal activity. The cell-free supernatants of B. nakamurai B4001 and B4022 strongly inhibited spore germination and mycelial growth of B. cinerea strains. The strong antifungal activity was linked to the lipopeptide families of iturins, surfactins, and fengycins. Conclusions This study shows that inter- and intra-specific variability in Bacillus spp. antifungal activity against B. cinerea is largely attributed to divergence in lipopeptide composition profiles. Most importantly, among the iturin families, a higher potency in bacillomycin D producing strains compared to iturin A producers was evident.