Bacillus subtilis and Bacillus amyloliquefaciens are useful tools in integrated control of grey mould in table-grape vineyards

The increasing interest on Biological Control Agents (BCAs) and natural products is linked to an increasing awareness on environmental and human health risks associated with the usage of synthetic chemicals. A deeper knowledge on the application of spray schedules based on the use of BCAs against plant pathogens might help in establishing their most properly and timely usage in Integrated Pest Management strategies. During 2013 and 2014, two field trials were carried out in table-grape vineyards located in Southern Italy. Different spray schedules were compared and the two Bacillus subtilis strain QST713 (Serenade Max, Bayer CropScience) and Bacillus amyloliquefaciens D747 (Amylo-X, Biogard BCB) were tested against grey mould either alone or in alternation or mixture with fungicides. Dynamics of BCA's populations was monitored by TaqMan-based nested qPCR assays. Both BCAs did not show satisfactory efficacy when used alone. However, their alternations with synthetic fungicides showed good levels of effectiveness in containing grey mould infections on bunches (prevalence lower than 22% during 2013 and 52% during 2014, at harvesting time), not different from reference chemical strategies (12% and 51% in the two years), as compared to the untreated check (up to 89%). No significant difference was observed between the two strategies in which BCAs applications preceded or followed fungicide sprays. Interestingly, the usage of BCAs contributed to reduce the occurrence of fungicide resistance in the pathogen’s populations and fungicide residues in grapes, an issue more and more required by big retailers operating on international markets. BCAs quantification showed comparable population dynamics in both trials, with both Bacillus strains able to survive on grape berries surface under the typical hot and dry summer climatic conditions in Apulia region, as well as at lower temperatures and higher humidity occurring at the end of the growing season in vineyards covered by plastic sheets to delay harvesting time until late Autumn. For both BCAs, density values of around 105 cells per mm2 of grape surface were reached soon after application and it generally decreased few days later to 103 cells per mm2. BCAs can be an effective integration to the use of fungicides in grey mould management, preventing the appearance and spread of fungicide-resistant B. cinerea strains, and reducing chemical residues in table grape.