Compound fermentation supernatants of antagonistic bacteria control Rhizoctonia cerealis and promote wheat growth

Abstract

Abstract Background Wheat sheath blight, caused by Rhizoctonia cerealis, is a popular fungal disease that causes serious harm to wheat production. Biological control can offer the safe and effective method to control wheat diseases. Results In this study, antagonistic bacteria XZ20-1 and XZ38-3 were isolated and identified as Bacillus amyloliquefaciens and Bacillus velezensis, respectively, and all produced cellulase, protease, amylase and siderophore. To improve antifungal activity, fermentation supernatants of antagonistic bacteria Pseudomonas fluorescens RB5 (previously isolated and stored in the laboratory), B. amyloliquefaciensns XZ20-1 and B. velezensis XZ38-3 were combined and the optimal compound ratio (2:6:4) was quickly screened out through the improved triangle coordinate diagram method. The inhibition rate of compound fermentation supernatants (CFS) reached 61.01%, which was 22.51, 17.05 and 21.42% higher than that of single strain, respectively. The further stability analysis showed that compound fermentation supernatants were relatively stable to pH, temperature, ultraviolet and light. Effect of CFS on pathogen cells through fluorescent microscopy using different stains revealed the mechanism, which CFS can cause cell membrane permeability changed, accumulation of ROS and DNA fragmentation. In the pot experiments, the control efficacy of CFS was 83.05%. Moreover, plant height, root length and fresh weight, chlorophyll and soluble protein of wheat seedlings in CFS treatment groups were more than those in the control group. Conclusions This work screened out the optimal compound ratio of fermentation supernatants by the improved triangular coordinate diagram method firstly and revealed the action mechanism and provides an effective microbial agent for controlling R. cerealis and promoting wheat growth.