In vitro screening of native rhizobacteria and selection of Bacillus atrophaeus for the biocontrol of pepper root rot in the Gansu Province, China

The aim of the present study was to screen native cultivable rhizobacteria with potential applications for biocontrol of root rot, which results in a serious and persistent disease problem for the pepper industry worldwide and is difficult to control through chemical and agricultural means. A total of 47 bacteria were isolated from pepper rhizosphere soil by spread plate and screened by dual culture assay. In in vitro dual culture assay, the strain DX1708 showed strong antagonistic activity against Fusarium oxysporum , F . solani , F . verticillioides , Phytophthora capsici and Rhizoctonia solani . Based on cultural and morphological characterization, and 16S rRNA gene and gyr A gene phylogenetic analysis strain DX1708 was identified as Bacillus atrophaeus . Strain DX1708 demonstrated many characteristics that are beneficial for plants, such as production of α -amylase, ammonia, cellulase, indole-3-acetic acid, pectinase, protease, siderophores, and phosphate solubilization. PCR-based detection of antimicrobial lipopeptides and peptides gene revealed the presence of ten genes in B . atrophaeus strain DX1708, which code for enzymes involved in production of bacilysin, fengycin, mycosubtilin, subtilosin and surfactin. In planta application of B . atrophaeus strain DX1708 significantly decreased root rot severity compared to untreated controls under greenhouse conditions. The strain DX1708 was tested in the field during three successive years (2018–2020). The results demonstrated a significant decrease in disease severity. These results suggest that B . atrophaeus strain DX1708 could control plant diseases via direct and indirect modes of action and can be used as a potential agent for biological control.