Pinus is an important economic tree species, but pine wilt disease (PWD) seriously threatens the survival of pine trees. PWD caused by Bursaphelenchus xylophilus is a major quarantine disease worldwide that causes significant economic losses. However, more information about its molecular pathogenesis is needed, resulting in a lack of effective prevention and treatment measures. In recent years, effectors have become a hot topic in exploring the molecular pathogenic mechanism of pathogens. Here, we identified a specific effector, BxNMP1, from B. xylophilus. In situ hybridization experiments revealed that BxNMP1 was specifically expressed in dorsal gland cells and intestinal cells, and RT–qPCR experiments revealed that BxNMP1 was upregulated in the early stage of infection. The sequence of BxNMP1 was different in the avirulent strain, and when BxNMP1-silenced B. xylophilus was inoculated into P. thunbergii seedlings, the disease severity significantly decreased. We demonstrated that BxNMP1 interacted with the thaumatin-like protein PtTLP-L2 in P. thunbergii. Additionally, we found that the β-1,3-glucanase PtGLU interacted with PtTLP-L2. Therefore, we hypothesized that BxNMP1 might indirectly interact with PtGLU through PtTLP-L2 as an intermediate mediator. Both targets can respond to infection, and PtTLP-L2 can enhance the resistance of pine trees. Moreover, we detected increased salicylic acid contents in P. thunbergii seedlings inoculated with B. xylophilus when BxNMP1 was silenced or when the PtTLP-L2 recombinant protein was added. In summary, we identified a key virulence effector of PWNs, BxNMP1. It positively regulates the pathogenicity of B. xylophilus and interacts directly with PtTLP-L2 and indirectly with PtGLU. It also inhibits the expression of two targets and the host salicylic acid pathway. This study provides theoretical guidance and a practical basis for controlling PWD and breeding for disease resistance.

Pine wilt disease (PWD) is greatly serious to Pinus, and there are still no effective therapeutic measures at present. It is necessary to explore a method of early diagnosis of PWD and to study rehabilitation treatment technology for diseased plants diagnosed early. This paper searched for infected pine trees in natural pine forests according to various subtle symptoms and divided the disease development stages. Different doses of 20% emamectin benzoate were injected at different stages, and the symptom development of pine trees was observed after injection. According to different external symptoms, the stage after being infected by PWD was divided into early stage I and II, middle stage I and II, late stage. It was shown by the results that the diagnostic rate of initial diagnosis based on the symptoms of early stage II was as high as 80%. Additionally, for early stage infected pine trees, an injection of 5–10 mL of 20% emamectin benzoate can inhibit the expansion of symptoms of PWD. One year after injection of 20 mL and 10 mL of 20% emamectin benzoate, the residues measured in the lateral branches 4 m above the injection point were 0.18 mg kg⁻¹ and 0.06 mg kg⁻¹, respectively. In summary, the characteristics of early stage II are ideal for identifying early infection, it has a certain therapeutic effect on early infected pine trees by injection of emamectin benzoate.