New strategies for protecting pine trees from pine wilt disease

点击翻译按钮获取中文摘要

Embolism in a microtomed pine (Pinus densiflora) section was recorded by a video-monitor under a microscope during counting the acoustic emission from the section. The event numbers were increased when embolism occurred. This observation led a conclusion that the embolism was not recovered in nematode inoculated pine trees while it does in the sound tree. Thus, this irreversible embolism splits water conducts and it results in the tree death.Systemic chemicals were screened by nematode inoculation test in pine (Pinus densiflora ) seedlings. We found that a new chemical was induced resistance against the nematode induced wilting in the seedlings. In 3-year-old nursery stocks, a commercial systemic chemical was effective against the wilting, the symptom of which was reduced, e.g., only dieback of the inoculated branches, delay of wilting. The chemical had induced nematicidal stilbenoids in the base of branches but not in young shoots. Thus, the base of branches plays important role for stopping the nematode movement. Another point is variation of the stilbenoid levels in the pine population. The variation suggest that nematode resistant lines may be selected by stilbenoid level.Because we found that stilbenoid formation is one of the key strategies for preventing pine wilt diseases, stilbene synthase genes, a step of which is a rate limiting for stilbenoid formation, were cloned from Pinus densiflora and characterized. Three new genes with full coding sequence was successfully expressed in E.coli. One of them was confirmed stilbene synthase activity. Thus the clones obtained will be available to construct a transgenic pine tree that carries resistance against pine wilt diseases.