关键词: 松材线虫病, 移动扩散, 早期诊断, 主干施药治疗, 修枝治疗

Abstract:

Objective: This study aims to reveal the relationship between the infestation and movement of Bursaphelenchus xylophilus in pine trees under natural environmental conditions and the symptomatic manifestation of the disease and treatment effect, and to explore the feasibility of implementing rehabilitation treatment at different stages of pine wilt disease, so as to provide scientific basis for the establishment of early diagnostic and treatment technology of pine wilt disease. Method: Ten-year-old Pinus massoniana was taken as the research object, and the top of the first-grade lateral branches was manually inoculated with pine wood nematode AMA3 (10 000/plant). Samples were taken at different symptomatic periods, and nematode densities at each site were determined by isolating and counting nematodes for analyzing the dynamics of nematode movement at different symptomatic periods and assessing the treatment effect of pruning the infected branches. At the same time, 21-year-old P. densiflora and P. thunbergii, which were naturally infected, were used for the study. The suspected infected twigs were collected, and morphological and molecular tests were used to confirm the diagnosis of pine trees at different symptomatic stages. For the diagnosed pine trees at different stages of infection, the control effects were analyzed using both single treatment (application of 34.1% emamectin benzoate stem injection granules solely to the trunk) and combined treatment (pruning of diseased twigs + application on the main trunk). Result: 1) Pre-episode stage: the pine tree was all green, nematodes were gathered near the inoculation point, there were no nematodes in the trunk, and the flow of turpentine was normal. Early stage I: the needles of inoculated twigs began to lose their green colour, nematodes moved from the inoculation point of the first level of lateral branches to the lower part of the plant, and there were almost no nematodes in the trunk, and the secretion of turpentine was slightly reduced. Early stage II: the needles of inoculated twigs became reddish-brown, the nematodes moved towards the main stem, there were a few nematodes in the main stem, and the secretion of turpentine was significantly reduced. Intermediate stage: the single inoculated twig withered, nearby twig needles discoloured, turpentine basically stopped secretion, and nematodes multiplied in the main trunk, and rapidly moved. Late stage: the whole plant needles withered more than 50% or the whole plant discoloured, no turpentine secretion, nematodes spread to the whole plant. 2) By pruning inoculated branches before the onset of disease, infected pines were able to eventually become symptom-free. Pruning at early stage I to mid-stage was able to delay the onset of disease in pines to varying degrees; and pruning at late stage was completely ineffective. 3) The survival rate of infected plants in the early stage of the disease was 100% with the combined treatment, and 50%~80% in the intermediate stage. Comparative tests at the mid-stage further revealed that the combination treatment was significantly better than single-agent treatment alone. Conclusion: There is a close relationship between the movement of B. xylophilus within pine trees and external symptoms, and the distribution characteristics of B. xylophilus are distinct at different stages of infection. During the early and mid-stages of infection in pine trees, the use of a combined treatment regimen yields significant therapeutic effects on diseased trees. This phenomenon provides practical application support for early diagnostic methods and treatment rehabilitation strategies for pine wilt disease.

Key words: pine wilt disease, mobile spread, early diagnosis, main stem application treatment, pruning treatment