Screening native Bacillus strains as potential biological control agents against ginger bacterial wilt and for promoting plant growth

Abstract

Bacterial wilt, caused by Ralstonia solanacearum, is a destructive disease that causes significant loss in ginger productivity. This disease is notoriously difficult to control by chemical measures, prompting the exploration of biological control as a more sustainable and effective alternative strategy. In our research, we aimed to develop effective microbial agents to combat R. solanacearum-induced bacterial wilt in ginger. Initially, 307 Bacillus-like strains were isolated from ginger rhizosphere soil. Among these, ten strains exhibited significant antibacterial activity after extensive in vitro screening, with Bacillus-like isolate F18 being the most effective. Further tests in a co-culture assay revealed six isolates, notably L70, that significantly reduced the pathogen's fitness. To further assess their effectiveness, six isolates of L3, L72, L73, F18, HC-5, and L70 were then subjected to a hydroponics assay, where they substantially lowered disease incidence in ginger seedlings, especially strains F18, HC-5, and L73. These three strains were identified as Bacillus velezensis, exhibiting beneficial traits such as IAA production, siderophore secretion, and phosphate and potassium solubilization. Additionally, they also harbored genes related to the production of the dipeptide bacilysin and the polyketides macrolactin, bacillaene and difficidin. In greenhouse experiments, these three B. velezensis strains, particularly F18 and HC-5, demonstrated remarkable efficacy in controlling bacterial wilt. Tubers soaked in these biocontrol agents showed reduced disease severity and pathogen population. Moreover, the treatments promoted ginger growth, notably in tuber fresh weight, with HC-5 showing the greatest improvement. Conclusively, this study suggests a highly efficient strategy for biologically controlling ginger bacterial wilt, with B. velezensis strains HC-5, L73, and F18 emerging as promising biocontrol agents.