Advances in research of pathogenic mechanism of pine wilt disease

Pine wilt disease, caused by the pinewood nematode, Bursaphelenchus xylophilus, is the most serious disease of pine tree with great economic losses. So far it is not clear why the pine trees turn wilting, though several hypotheses about the pathogenicmechanism of pine wilt disease have been presented, such as phytotoxins causing death of pine trees; cellulases hydrolyzing celluloses of pine tree; terpenoids causing cavitation and water column breakage of pine tree, etc. Recently, it was found that certain bacteria, symbiotically associated with the pinewood nematode, may play some roles in the pathogenicity of the disease. Since the pine wilt disease is a complex interrelationships among beetle, pine tree, fungi, bacterium and nematode, all the pathogenic factors are not mutually exclusive, which means a variety of factors make pine tree for death, rather than a single factor. Pinewood nematode and bacteria produce phytotoxins and cellulases, which cause the defense of pine tree and stimulate the production of terpenoids to form cavitation, break water columns and finally make pine trees wilting. Pinewood nematode is involved in the production of phytotoxins, cellulases and terpenoids; therefore it is a vital and indispensable factor for pine wilting disease.   Key words: Pinewood nematode, Bursaphelenchus xylophilus, pathogenic mechanism, terpenoid, cavitation, cellulase, phytotoxin, bacteria.