Bursaphelenchus xylophilus

Bursaphelenchus xylophilus, commonly known as pine wood nematode or pine wilt nematode (PWN), is a species of nematode that infects trees in the Pinus genus of coniferous trees and causes the disease pine wilt. While native to North America, it spread in the early 20th century to Japan and in the latter half of the century to other areas of Asia, including China, Taiwan, and Korea, as well as to Europe, including Portugal and Spain. Pine mortality in Japan was first reported by Munemoto Yano (矢野宗幹) in Nagasaki prefecture in 1905. The nematode was first discovered in the timber of longleaf pine (Pinus palustris) in Louisiana, United States. Steiner and Burhrer reported that the nematode was a new species, and they named it Aphelenchoides xylophilus in 1934. In 1969, Japanese plant pathologists Tomoya Kiyohara (清原友也) and Yozan Tokushige (徳重陽山) discovered many unfamiliar nematodes on dead pine trees around the Kyushu islands in Japan. Then, they experimentally inoculated the nematode to healthy pine and other conifer trees and observed them. The healthy pine trees were killed—especially Japanese red pine (Pinus densiflora) and Japanese Black pine (P. thunbergii). However, Jack pine (P. banksiana), Loblolly pine (P. taeda), Sugi redwood (Cryptomeria japonica), and Hinoki cypress (Chamaecyparis obtusa) trees were able to survive. In 1971, the researchers concluded that the nematode was the pathogen was the primary contributor to the high mortality of Japanese pine trees. In 1972, Yasuharu Mamiya (真宮靖治) and Kiyohara incorrectly claimed that the nematode was a new species, which they named Bursaphelenchus lignicolous. A 1981 reclassification united the American and Japanese forms as B. xylophilus. Pine wilt nematode epidemics have occurred in Japan, particularly during warm, dry summers. In the late 1970s and 1980s, the nematode was observed to have spread to other countries of Asia outside of Japan, including China, Taiwan, and Korea, and later observed in Europe, including Portugal and Spain.