Differential induction of grapevine resistance and defense reactions against Botrytis cinerea by bacterial mixtures in vineyards

Previous experiments showed that seven bacteria identified as Acinetobacter lwoffii (PTA-113 and PTA-152), Bacillus subtilis (PTA-271), Pantoea agglomerans (PTA-AF1 and PTA-AF2) and Pseudomonas fluorescens (PTA-268 and PTA-CT2) induced systemic resistance in grapevine against Botrytis cinerea. Based on these findings, we investigated biocontrol capacity of different mixtures under vineyard conditions over three consecutive years. Treatments with bacterial mixtures were shown to induce systemic resistance against B. cinerea on year 2. Efficacy and duration of such a disease control seemed to be reinforced on year three without renewal of bacterial treatments. Accordingly, the effectiveness of induced resistance varied with mixture type of bacteria and was accompanied by a stimulation of chitinase and β-1,3 glucanase activities in both leaves and berries. Interestingly, treatments with mixtures containing both selected strains of P. agglomerans (PTA-AF1 + PTA-AF2) appeared as the most effective in triggering systemically the plant defense reactions and reducing the symptoms of grey mould disease.