Biocontrol activity of anti-salinity Bacillus mesonae H20-5 against Bacterial wilt in different tomato cultivars

•Bacillus mesonae H20-5 suppressed bacterial wilt in ‘Mairokku’ of tomato plants.•Strain H20-5 accumulated polyphenol and lawsone in ‘Mairokku’ after inoculation.•Strain H20-5 induced salinity tolerance in the tested cultivars. Bacterial wilt caused by Ralstonia solanacearum and soil salinity are critical problems associated with the cultivation of tomato plants in Korea. In our previous study, we demonstrated the alleviation of salinity stress by Bacillus mesonae H20-5 in tomato plants. In this study, we investigated the effects of strain H20-5 on disease suppression and salinity stress in two different cultivars, which are susceptible (‘Juiken’) and moderately resistant (‘Mairokku’) to bacterial wilt. The results showed that H20-5 exhibited antibacterial activity against R. solanacearum, where the strain significantly suppressed bacterial wilt only in moderately resistant (‘Mairokku’) but not in susceptible cultivar (‘Juiken’). Moreover, only H20-5-treated moderate resistant cultivar (‘Mairokku’) plants observed an increase in the expression levels of defense-related genes, phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO), and accumulated polyphenols and lawsone after R. solanacearum inoculation. In contrast, under salinity condition, the H20-5-treated two cultivars mitigated the decrease in plant growth and pigment content, and regulated the concentration of the major divalent cation Mg2+. These findings demonstrated that B. mesonae H20-5 could alleviate salinity stress in cultivars regardless of their resistance to R. solanacearum; however, the biocontrol activity was seemingly dependent on cultivar resistance by strongly enhancing resistance related responses, such as regulating expression of PAL and PPO, and accumulating polyphenol and lawsone in the moderately resistant cultivar (‘Mairokku’) compared to susceptible cultivar (‘Juiken’). Therefore, the strain H20-5 could improve the resistance of the cultivar against R. solanacearum, whereas it alleviated salinity stress regardless of the resistance of tomato cultivars.