Screening and Regulatory Mechanisms of Inter-Root Soil Nematicidal Bacteria of Pinus massoniana

Abstract

Pine Wilt Disease (PWD), caused by the pathogenic nematode Bursaphelenchus xylophilus, is a systemic infectious disease commonly referred to as the “cancer” of pine trees. This devastating disease has gained this analogy due to its ability to rapidly spread within pine populations, leading to substantial losses in forest resources. The primary objective of this study is to investigate the bioprotective potential and underlying mechanisms of action exhibited by rhizosphere microorganisms associated with Masson pine (Pinus massoniana) in the context of controlling the pine wilt nematode. In this experiment, using high-throughput sequencing, significant differences were observed in the rhizosphere soil microbial communities among healthy Masson pine, standing dead trees, and diseased Masson pine. Furthermore, it was found that these microbial communities exhibited distinct community structures at different levels. This study successfully isolated and screened three strains of highly effective nematophagous bacteria from the rhizosphere soil. The identified strains were Lysinibacillus capsici, Bacillus Paramycoides, and Delftia tsuruhatensis. After applying the bacterial suspensions and fermentation extracts of these three strains to the roots of two-year-old Masson pine seedlings, followed by inoculation with pine wilt nematodes after a four-day period, distinct defense responses were observed in the Masson pine. Notably, the activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD) were significantly increased, leading to a substantial reduction in the incidence of pine wilt disease. Based on the changes in defense enzyme activities, it can be concluded that the fermentation extract of the Lysinibacillus capsici strain exhibits effective nematocidal effects and induces resistance. The significant biological control efficacy and induction of host defense activity indicate the potential application value of this strain and its metabolites as a biocontrol agent for pine wilt disease.