Isolation and Identification of Antagonistic Bacteria with Common Bacterial Blight of Common Bean and Their Mechanism as Biological Control

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) and Xanthomonas fuscans subsp. fuscans (Xff), is a devastating disease threatening global common bean (Phaseolus vulgaris L.) production. Current reliance on copper-based chemicals has led to environmental toxicity and pathogen resistance, resulting in the need for sustainable alternatives. Here, we report the first biocontrol strain of Bacillus amyloliquefaciens (KY2) that is simultaneously effective against both Xap and Xff. Isolated from the rhizosphere of healthy common bean growing in a high-disease-incidence field, KY2 exhibited broad antagonism, with inhibition zones of 18.17 ± 0.58 mm and 24.00 ± 1.50 mm against Xap and Xff, respectively. Pot experiments revealed a 66.12% curative control efficacy against Xff, slightly lower than the chemical agent 12% Zhongshengmycin. Mechanistically, KY2 alleviated oxidative stress by enhancing antioxidant enzyme activity levels and reducing malondialdehyde accumulation. A transcriptome analysis further uncovered KY2-induced systemic resistance via phenylpropanoid biosynthesis and defense-related pathways. It also demonstrated adaptability to pH 4–8, 20–40 °C, and ≤6% NaCl. However, this study is limited to pot trials, necessitating future field validation to assess practical scalability. These findings establish KY2 as a novel, eco-friendly candidate for CBB management, advancing biocontrol strategies against CBB of bean.