The Effect of Bacillus subtilis and Bacillus velezensis on the Antioxidative Responses of Tomato Plants Facing Pseudomonas syringae pv. tomato DC3000 Infection

Tomato (Solanum lycopersicum), a globally significant crop, is highly susceptible to bacterial speck disease caused by Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). In this paper, we studied the effect of plant growth-promoting bacteria (PGPB) Bacillus subtilis MGMM36 and Bacillus velezensis MGMM30 on tomato resistance to Pst DC3000 under greenhouse conditions. Seed pre-treatment with either B. subtilis or B. velezensis improved plant viability (60% and 50% survival, respectively, compared to 25% in plants infected with Pst DC3000 alone) and mitigated pathogen-induced damage. B. subtilis provided stronger protection compared to B. velezensis: plants treated with B. subtilis showed a 20% reduction in shoot length (SL), a 10% reduction in root length (RL) and a 15% reduction in leaf area (LA) compared to the control. However, plants treated with B. velezensis exhibited a 30% decrease in SL, a 25% decrease in RL and a 22% decrease in LA. Furthermore, in infected plants grown from seeds previously treated with PGPB, no increase in CAT (SICAT), SOD (SISOD) and PTO gene expression was observed, in contrast to untreated plants. Both B. subtilis and B. velezensis increased the expression of the PR1 gene, restoring it to levels found in uninfected control plants. These findings underscore the potential of two strains of Bacillus spp. as sustainable biological agents to enhance disease resistance and promote tomato growth, with the aim of practical application for pesticide reduction and environmental protection.