Archivio Journal of Plant Pathology

Abstract:

The bacterial antagonists (Bacillus subtilis GB03, B. subtilis QST713, B. subtilis Y1336 and Pantoea agglomerans P10c) and plant defense activators (acibenzolar-S-methyl (ASM), fosetyl aluminium (F-Al), potassium phosphites (PH) and prohexadione-Ca (ProCa)) were evaluated individually and in combination for efficacy in controlling fire blight in Morocco. Under laboratory conditions, on detached blossoms of apple and pear, only biocontrol treatments based on P. agglomerans P10c and their mixture with B. subtilis QST713 showed a significant reduction in the incidence of the disease when compared to other treatments. Under field conditions, both the above mixture of biocontrol agents as well as all other strains were tested alone or combined with plant defense activators using a split-split-plot design. The treatments were applied on the trees at timings based on their modes of action. Results showed that, when used alone, P. agglomerans P10c, B. subtilis QST713, their mixture (1:1), B. subtilis GB03 and B. subtilis Y1336 reduced blossom infection under field conditions by 66, 63.8, 61.7, 64.2, and 53% respectively. For plant defense activators this reduction was 61.5, 56.6, 50 and 49% for ASM, ProCa, F-Al and PH, respectively. On shoots, it ranged from 40 to 80% for biocontrol agents, but for plant defense activators it varied from 46 to 96.5%. Two individual applications of ProCa were the most effective treatment for reducing shoot blight incidence. The combination of plant defense activators and biocontrol agents allowed the highest protection rate against blossom and shoot blight ranging from 76 to 98.2%. The greatest protection was insured by B. subtilis QST713, P. agglomerans P10c or their mixture combined with ASM or ProCa.