AUTHOR=Jia Shu , Song Ce , Dong Hai , Yang Xujie , Li Xinghai , Ji Mingshan , Chu Jin 

TITLE=Evaluation of efficacy and mechanism of Bacillus velezensis CB13 for controlling peanut stem rot caused by Sclerotium rolfsii

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1111965

DOI=10.3389/fmicb.2023.1111965

ISSN=1664-302X

ABSTRACT=<p>Peanut stem rot, caused by <italic>Sclerotium rolfsii</italic>, considerably affects crop productivity. Application of chemical fungicides harms the environment and induces drug resistance. Biological agents are valid and eco-friendly alternatives to chemical fungicides. <italic>Bacillus</italic> spp. are important biocontrol agents that are now widely used against several plant diseases. This study aimed to evaluate the efficacy and mechanism of a potential biocontrol agent <italic>Bacillus</italic> sp. for controlling peanut stem rot caused by <italic>S. rolfsii</italic>. Here, we isolated a strain of <italic>Bacillus</italic> from pig biogas slurry that considerably inhibits the radial growth of <italic>S. rolfsii</italic>. The strain CB13 was identified as <italic>Bacillus velezensis</italic> on the basis of morphological, physiological, biochemical characteristics and phylogenetic trees based on the 16S rDNA and <italic>gyrA</italic>, <italic>gyrB</italic>, and <italic>rpoB</italic> gene sequences. The biocontrol efficacy of CB13 was evaluated on the basis of colonization ability, induction of defense enzyme activity, and soil microbial diversity. The control efficiencies of <italic>B. velezensis</italic> CB13-impregnated seeds in four pot experiments were 65.44, 73.33, 85.13, and 94.92%. Root colonization was confirmed through green fluorescent protein (GFP)-tagging experiments. The CB13-GFP strain was detected in peanut root and rhizosphere soil, at 10<sup>4</sup> and 10<sup>8</sup> CFU/g, respectively, after 50 days. Furthermore, <italic>B. velezensis</italic> CB13 enhanced the defense response against <italic>S. rolfsii</italic> infection by inducing defense enzyme activity. MiSeq sequencing revealed a shift in the rhizosphere bacterial and fungal communities in peanuts treated with <italic>B. velezensis</italic> CB13. Specifically, the treatment enhanced disease resistance by increasing the diversity of soil bacterial communities in peanut roots, increasing the abundance of beneficial communities, and promoting soil fertility. Additionally, real-time quantitative polymerase chain reaction results showed that <italic>B. velezensis</italic> CB13 stably colonized or increased the content of <italic>Bacillus</italic> spp. in the soil and effectively inhibited <italic>S. rolfsii</italic> proliferation in soil. These findings indicate that <italic>B. velezensis</italic> CB13 is a promising agent for the biocontrol of peanut stem rot.</p>