Biocontrol of Meloidogyne incognita by Bacillus velezensis TA-1 through induction of host resistance in tomato

Meloidogyne incognita is among the most detrimental parasitic nematodes with a wide host range causing huge economic losses annually. Biological control of M. incognita has emerged as a promising alternative in sustainable agriculture. In our previous study, Bacillus velezensis TA-1 effectively controlled M. incognita in vitro and in the field trials through direct nematocidal activities. However, it remains poorly understood for the underlying mechanisms including whether TA-1 could induce host resistance against M. incognita. In the present study, the effects of TA-1 induced resistance against M. incognita in tomato were determined. Results showed that TA-1 colonized tomato roots, with 1.23 × 10⁸ colony forming units (CFU)/g root tissues attached within 36 h, significantly reduced the number of galls in the local and systemic root systems in the split-root experiments by 44.0% and 28.1%, respectively. The bacteria also increased the basic defense responses of tomato plants, such as lignin accumulation and hydrogen peroxide (H₂O₂) content, which was associated with the enhanced activities of enzymes related to plant defense [e.g. phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO)]. Moreover, TA-1 enhanced the expressions of tomato defense response genes in the salicylic acid (PR1a and PR-P6) and jasmonic acid (PI II and MC) pathways and induced resistance against M. incognita. These results suggested that TA-1 could effectively control M. incognita through induction of tomato resistance, therefore it could be used as a promising biocontrol agent to be incorporated in the integrated management programs in tomato production.