Bacillus amyloliquefaciens Ba13 induces plant systemic resistance and improves rhizosphere microecology against tomato yellow leaf curl virus disease

Abstract

The control effect of Bacillus against tomato yellow leaf curl virus (TYLCV) disease has not been reported. It is not clear whether adjustment of the rhizosphere microbial community structure by beneficial microbes applied as biocontrol agents is related to their role in increasing resistance of plants to viral diseases. Therefore, the objective of this study was to investigate the control effect and mechanism of Bacillus amyloliquefaciens Ba13 against TYLCV disease. Two treatments including control and Ba13 treatment followed by natural infection with whiteflies were conducted. We measured plant growth, physiological parameters, disease severity, and leaf virus quantity and also assayed resistance-related gene expression, defense enzyme activity, and rhizosphere microbial community structure. Strain Ba13 lowered the infection rate, disease severity, and leaf virus quantity in tomato plants, with the control rate of 48–52%. Root development and shoot biomass markedly improved in tomato following Ba13 treatment. Ba13 elevated expression of pathogenesis-related PR1, PR2, and PR3 genes, and enhanced activities of phenylalanine ammonia lyase, polyphenol oxidase, peroxidase, β-1,3 glucanase, and chitinase in tomato leaves. Cultivation-dependent microbiological analysis showed that Ba13 increased the bacteria-to-fungi ratio and the number of beneficial microbes while decreasing the number of pathogenic fungi in the rhizosphere. Further analysis revealed the potential of a dominant rhizosphere bacterium, B. velezensis B3, to promote plant growth and improve systemic resistance in tomato. B. amyloliquefaciens Ba13 can enhance plant resistance against TYLCV disease through direct induction of systemic resistance and also by increasing the number of beneficial microbes in the rhizosphere, thereby achieving control of TYLCV disease.