Pathology of the Pine Wilt Disease Caused by Bursaphelenchus xylophilus.

Abstract

Wilt diseases are much less common in gymnospermous species of trees than in Angiosperms. To date, only two wilt diseases of pines have been reported­ one caused by blue-stain fungi of the genus Ceratocystis (2) and the other caused by a nematode-Bursaphelenchus xylophilus. Both the fungus and the nematode wilt diseases develop after attack of trees by insects-bark beetles in the case of the fugus disease and pine sawyer in the case of the nematode disease. The pine wilt caused by the nematode, is the most serious disease of forest trees in Japan. In 1981, the annual loss of pines amounted to 2 million m3, with the death of nearly 10 million trees. This devastating epidemic of pine wilt disease has spread throughout Japan in stands of native pines-Pinus densijlora, P. thunbergii, and P. luchuensis. Areas infested by disease are estimated to have reached 650,000 ha, that is 25% of this nation's total of 2.6 million h a o f pine forest. The first occurrence of pine wilt disease in Japan dates back to 1905 when Yano (126) reported an outbreak of diseased pine trees in Nagasaki, Kyushu. Although he did not determine the cause, he described disease symptoms that correspond well with those currently induced by the pinewood nematode. Since then, infested areas have spread progressively along the coastal areas of southwestern Japan, and to inland areas of low elevation. The infestation now extends into the northern region of Honshu. The disease has been spread to remote areas by the importation of pine logs infested with the pine wood nematode.