Bacillus velezensis CC09: A Potential 'Vaccine' for Controlling Wheat Diseases

Biocontrol bacteria that can act like a vaccine, stimulating plant resistance to pathogenic diseases, are still not fully elucidated. In this study, an endophytic bacterium, Bacillus velezensis CC09, labeled with green fluorescent protein, was tested for its colonization, migration, and expression of genes encoding iturin A synthetase within wheat tissues and organs as well as for protective effects against wheat take-all and spot blotch diseases. The results showed that strain CC09 not only formed biofilm on the root surface but was also widely distributed in almost every tissue, including the epidermis, cortex, and xylem vessels, and even migrated to stems and leaves, resulting in 66.67% disease-control efficacy (DCE) of take-all and 21.64% DCE of spot blotch. Moreover, the gene cluster encoding iturin A synthase under the control of the p(itu) promoter is expressed in B. velezensis CC09 in wheat tissues, which indicates that iturin A might contribute to the in-vivo antifungal activity and leads to the disease control. All these data suggested that strain CC09 can act like a 'vaccine' in the control of wheat diseases, with a single treatment inoculated on roots through multiple mechanisms.