Suppression of tomato bacterial speck disease (Pseudomonas syringae pv. tomato (Okabe) Young, Dye, & Wilkie) via induced systemic resistance by Pseudomonas and Bacillus strains

Bacterial speck Pseudomonas syringae pv. tomato (Pst) (Okabe) Young, Dye, & Wilkie is a widespread disease in tomato plants. Four plant growth-promoting rhizobacterial (PGPR) strains 5(3), 68(2), 36(1), and 47(3) played a significant role (50% and higher) in reducing spot disease severity. Selected strains were identified as Pseudomonas koreensis 5(3), Bacillus mycoides 68(2), Bacillus mojavensis 36(1), and Bacillus simplex 47(3) using the MALDI Biotyper classification system. In planta assay using tomato seedlings were inoculated with the bacterial strains alone or in dual combination. Pseudomonas koreensis 5(3) (51.9%-74.29%) and Bacillus mycoides 68(2) (36.70%-65.56%) both provided a significant reduction in foliar severity caused by bacterial speck disease agent Pseudomonas syringae pv. tomato (Okabe) Young, Dye, & Wilkie. Bacillus simplex 47(3) and Bacillus mojavensis 36(1) were successful only in combined treatments. Defense enzymes Proline, Peroxidase, and Catalase were induced by PGPR strains in comparison with those of control plants. Hydrogen peroxide (H2O2) and callose deposition were evident at reaction sites induced by PGPR strains. The accumulation of callose, H2O2, and high levels of defense enzymes via the treatment of PGPRs might play a significant role in a practical, safe, and effective way to control Pseudomonas syringae pv. tomato.