Growth inhibition and induction of systemic resistance against Pythium aphanidermatum by Bacillus simplex strain HS-2

ABSTRACTBiological control of plant disease with plant growth-promoting rhizobacteria (PGPR) has increasingly become noteworthy as they provide an alternative and supplement to synthetic chemicals without environmental contamination. Numerous Bacillus species have been used for seed treatment, induction of systemic resistance and suppression of both root and foliar disease-causing organisms. As a Bacillus species, Bacillus simplex also features antifungal and plant growth-promoting activities, but its ability to induce systemic resistance remains obscure. In this study, a Bacillus simplex strain HS-2 was isolated with both in vitro and in vivo activities against Pythium aphanidermatum in tobacco. The early plant defence responses were investigated to further illuminate the mechanisms by which the strain confers plant protection. Results showed that HS-2 primed tobacco for pathogen challenge through enhancing reactive oxygen species production and callose deposition in roots, that is, establishing a system...