Exploration of epiphytic bacteria of stone fruit trees for biocontrol of Pseudomonas syringae pv. syringae

Bacterial canker of stone fruits caused by Pseudomonas syringae pv. syringae (Pss) is one of the most important diseases of fruit trees worldwide. Despite its significant economic impact, chemical control methods using copper compounds remain often ineffective. Biological control provides a powerful and environmentally friendly alternative to synthetic pesticides. This study sought to isolate and identify epiphyte bacteria from the tissue surface of leaves and shoots of stone trees and investigate their antagonistic effects against pathogenic Pss in laboratory and greenhouse conditions. In vitro analysis of the antagonistic activity of 122 epiphytic bacterial strains showed that 36.78% of strains could produce inhibition zone diameter from 20 to 50 mm towards Pss. Also, some strains produced antibiotic and volatile organic antimicrobial compounds. The antagonist strains were identified as Pseudomonas sp., Acinetobacter sp., Stenotrophomonas sp. and Pantoea agglomerans due to the physiological and biochemical characteristics and the partial 16SrRNA gene sequence. In vivo tests, the antagonistic Pseudomonas sp. strain 145c and Acinetobacter sp. strain 147b reduced the disease severity of bacterial canker of stone fruit on two-year-old peach trees by 94.80% compared to the positive control. This study demonstrates that epiphytic bacteria from stone fruit trees exhibit strong potential for controlling Pss. These strains have the potential to serve as significant biocontrol agents.