Anaerobic soil disinfestation rather than Bacillus velezensis Y6 inoculant suppresses tomato bacterial wilt by improving soil quality and manipulating bacterial communities

Continuous cropping leads to high incidence of soilborne diseases such as bacterial wilt caused by Ralstonia solanacearum, which poses a risk to agricultural production. Anaerobic soil disinfestation (ASD) and plant growth-promoting rhizobacteria (PGPR) are considered environmentally friendly methods to control bacterial wilt. However, the underlying mechanism of the improvement of soil health and the inhibition of bacterial wilt after ASD treatment and PGPR inoculation needs further exploration. This study evaluated the effect of ASD treatment on soil improvement at pre-planting of tomato, and the effect of ASD treatment combined with the application of Bacillus velezensis Y6 (BV) on soil quality, R. solanacearum abundance, and bacterial communities at 90 days before harvesting of tomato. The results showed that ASD treatment reduced R. solanacearum abundance in soil by 17.6% at pre-planting and 18.7% at 90 days before harvesting, but BV inoculation did not influence R. solanacearum abundance. ASD and ASD+BV treatments effectively reduced the occurrence of bacterial wilt, improved soil nutrient status and increased soil microbial activity at 90 days before harvesting. Principal co-ordinate analysis showed that the soil bacterial community was significantly influenced by ASD treatment both at pre-planting and at 90 days before harvesting. Further investigation found that ASD contributed to the enrichment of beneficial flora (Bacillus and Streptomyces). Moreover, pH was an important environmental factor affecting the abundance of R. solanacearum in soil. Co-occurrence network analysis showed that ASD treatment significantly increased network connection of bacterial communities and the proportion of beneficial microorganisms (Proteobacteria and Firmicutes), leading to complex soil bacterial co-occurrence networks both at pre-planting and at 90 days before harvesting. Collectively, these results indicate that ASD treatment, but not microbial inoculation can enhance tomato plant resistance to bacterial wilt by improving soil quality and modulating the soil bacterial community.