Study on the Virulence Variation of Isolated Species of Pine Wood Nematode in Several Subultures

In this study the virulence of pine wood nematode(Bursaphelenchus xylophilus) was measured with the artificial inoculation of 2-year Japanese black pine(Pinus thunbergii)and the causes for virulence variation of pinewood nematode in several subcultures were analyzed.The results showed that: the breeding rate of pine wood nematode in several subcultures was 5～6 days slower than that of pine wood nematode in primary culture;the reproductive capacity was substantially reduced and the number of proliferated pine wood nematode per culture dish was averagely 410,000.The number in primary culture was 1.24 million.Its traveling speed in the water was slow and its retention time was short,indicating the pine wood nematode in several subcultures had poor vitality and indicating the virulence of pine wood nematode greatly depended on its proliferation and vitality,when the subculture was carried out for a long time,its virulence had a sharp decline after 15 times.