Nematicidal activity of <italic>Peribacillus frigoritolerans</italic> Rhs-L31 on <italic>Bursaphelenchus xylophilus</italic> and control effect against pine wilt disease

To explore the nematocidal activity and biocontrol potential of strain Rhs-L31 against Bursaphelenchus xylophilus, the strain Rhs-L31 was identified by morphology and 16S rDNA sequence analysis. The nematocidal activity, reproductive inhibition ability of the strain Rhs-L31 against B. xylophilus and effect on lipid droplet morphology in B. xylophilus bodies were determined by the treatment of fermentation broth and fermentation filtrate. The control effect of Rhs-L31 fermentation broth on Pinus tabuliformis seedlings and the effects of Rhs-L31 fermentation broth on the activities of related defense enzymes in P. tabuliformis were evaluated by pot experiment. The results showed that strain Rhs-L31 was preliminarily identified as Peribacillus frigoritolerans. Fermentation broth and fermentation filtrate exhibited strong nematocidal activity against B. xylophilus and the corrected mortality was both as high as 100 % at 24 h after treatment. The corrected mortality of B. xylophilus was 76.90 % and 72.60 % at 24 h after treatment with Rhs-L31 fermentation broth and fermentation filtrate diluted five times, respectively. Fermentation broth and fermentation filtrate significantly reduced the reproduction coefficient and egg number of B. xylophilus. Oil red O staining showed that Rhs-L31 fermentation broth and fermentation filtrate could destroy the lipid droplet morphology in B. xylophilus; pot experiments showed that fermentation broth injection treatment could significantly reduce the occurrence of pine wilt disease, and the control effect was 52.08%-83.33% for 14-35 days after treatment. Rhs-L31 fermentation broth could significantly reduce the density of B. xylophilus in P. tabuliformis seedlings, and the density of B. xylophilus in the prevention group was significantly lower than that in the control group. Rhs-L31 enhanced the activities of polyphenol oxidase, catalase, superoxide dismutase and peroxidase in P. tabuliformis seedlings against B. xylophilus. The results revealed that strain Rhs-L31 had potential for biocontrol of pine wilt disease, which could provide a reference for the development of efficient and green prevention and control technology of pine wilt disease.