Root-irrigation with Bacillus velezensis TX2 induces systemic resistance to soft rot disease via jasmonic acid and salicylic acid dependent pathways in Colocasia esculenta

Pectobacterium carotovorum (Pcc) is the causative organism of bacterial soft rot disease, one of the most hazardous diseases affecting Colocasia esculenta (L.) Schott. Currently, chemical fungicides are still useful in controlling soft rot disease, but their constant usage not only makes bacteria more resistant but also poses risks to the ecosystem. Plant growth-promoting rhizobacteria (PGPRs), however, provide an alternative for disease control and sustainable development. In this investigation, we obtained an isolate of Bacillus velezensis (TX2) from the soil of the taro rhizosphere. In C. esculenta, TX2 root-irrigation was then shown to stimulate auxin production and plant growth. More interestingly, it was discovered that taro developed resistance to Pcc following this TX2 root-irrigation treatment. Through whole genome sequencing, we found 13 homologous genes related to biosynthesis of plant growth-promoting and resistant secondary metabolite. Furthermore, TX2 application was confirmed to enhance the expression of resistant marker genes PDF1.2, PR1 and PR2 by transcriptomic analysis as well as qRT-PCR verification. The concentrations of JA, JA-Ile, and SA were also raised significantly in taro plants with the application of TX2. Collectively, our results showed that TX2 enhances taro plant resistance to soft rot by strengthening the SA and JA pathways and may serve as a promising biocontrol agent.