Bacillus velezensis SYL-3 suppresses Alternaria alternata and tobacco mosaic virus infecting Nicotiana tabacum by regulating the phyllosphere microbial community

Abstract

The occurrence of plant diseases is closely associated with the imbalance of plant tissue microecological environment. The regulation of the phyllosphere microbial communities has become a new and alternative approach to the biological control of foliar diseases. In this study, <i>Bacillus velezensis</i> SYL-3 isolated from Luzhou exhibited an effective inhibitory effect against <i>Alternaria alternata</i> and tobacco mosaic virus (TMV). The analysis of phyllosphere microbiome by PacBio sequencing indicated that SYL-3 treatment significantly altered fungal and bacterial communities on the leaves of <i>Nicotiana tabacum</i> plants and reduced the disease index caused by <i>A. alternata</i> and TMV. Specifically, the abundance of <i>P. seudomo</i>, <i>Sphingomonas</i>, <i>Massilia</i>, and <i>Cladosporium</i> in the SYL-3 treatment group increased by 19.00, 9.49, 3.34, and 12.29%, respectively, while the abundances of <i>Pantoea</i>, <i>Enterobacter</i>, <i>Sampaiozyma</i>, and <i>Rachicladosporium</i> were reduced. Moreover, the abundance of beneficial bacteria, such as <i>Pseudomonas</i> and <i>Sphingomonas</i>, was negatively correlated with the disease indexes of <i>A. alternata</i> and TMV. The PICRUSt data also predicted the composition of functional genes, with significant differences being apparent between SYL-3 and the control treatment group. Further functional analysis of the microbiome also showed that SYL-3 may induce host disease resistance by motivating host defense-related pathways. These results collectively indicate that SYL-3 may suppress disease progression caused by <i>A. alternata</i> or TMV by improving the microbial community composition on tobacco leaves.