Use of Bacillus velezensis SDTB022 against tobacco black shank (TBS) and the biochemical mechanism involved

Abstract

Induced resistance (IR) is a defense against diseases that stimulate the overexpression of related resistance genes in plants to enhance their defense capabilities against multiple pathogens. We identified strain SDTB022 which has good biocontrol effects and was stored in our laboratory as Bacillus velezensis based on physiological and biochemical tests and the 16S rRNA, gyrA and gyrB genes. We found that SDTB022 had a poor direct inhibitory effect against the mycelial growth of Phytophthora parasitica var. nicotianae, the causal agent of tobacco black shank (TBS). Interestingly, B. velezensis SDTB022 promoted plant growth in the greenhouse and increased plant yield and disease defense responses in the field. After treatment with SDTB022, the activities of defense enzymes in tobacco, such as polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia-lyase (PAL), significantly increased. However, the MDA content in tobacco decreased. In addition, quantitative real-time PCR results showed that the tobacco PR1a, PR3 and PR5 genes were upregulated, the PDF1.2 gene was downregulated, and SA-dependent signal transduction pathways induced systemic acquired resistance and disease resistance throughout the entire plant. These results indicate that the PGPR strain B. velezensis SDTB022 can effectively control TBS disease by inducing tobacco resistance. B. velezensis SDTB022 can possibly be used as a biological pesticide against TBS disease in modern agriculture.