Screening of larch endophytic bacteria with nematicidal activity against Bursaphelenchus xylophilus and the biocontrol potential for pine wilt disease

Pine wilt disease (PWD), caused by Bursaphelenchus xylophilus (PWN), leads to severe ecological and economic losses. Current control methods rely on chemical nematicides, which pose environmental and health risks and have led to PWN resistance, reducing their field efficacy. A green and effective strategy is urgently needed. A highly effective nematicidal strain, SD30, was screened. Its fermentation broth achieved a nematicidal rate of 100% after 12 h and the same result after 24 h for the filtrate. The bacterial suspension showed a 76.60% nematicidal rate after 48 h. SD30 was identified as Bacillus thuringiensis through morphological and molecular methods. In indoor efficacy tests on Pinus massoniana, the bacterial suspension exhibited a control efficacy of 54.74%, outperforming both the fermentation broth and filtrate. When applied 7 days before inoculation, the bacterial suspension achieved a 67.00% control efficacy, more effective than when applied 3 days before, on the day, or after inoculation. The highest control efficacy (52.00%) was observed at a concentration of 3 × 107 cfu mL-1, with efficacy decreasing at higher dilutions. Indoor control efficacy on Masson pine and larch was 67.74% and 73.68%, respectively, with better results on larch. In safety evaluations, Bt SD30 showed no pathogenicity to tobacco and alfalfa, was sensitive to six antibiotics, exhibited weak hemolytic activity, and contained the virulence genes nheB, nheC and entFM. This study screened out Bt SD30 from larch, which demonstrates strong nematicidal activity and holds potential for biocontrol applications against pine wilt disease. © 2025 Society of Chemical Industry.