Twenty populations of Bursaphelenchus mucrunatus collected from China, Japan, Canada, Korea, France and Norway were tested for pathgenicity to 2-year-old seedling of Pinus thunbergii. The populations were divided into three groups according to the pathogenicity. The strongest pathogenicity was observed in BmFr, BmCGHH, BmCFJ2 and BmFJ3. Their mortality rates was more than 85% and RHS index was over 100. The second group included BmCZZ, BmCHN, BmCWY1, BmCWY2, BmCWY4, BmCNJ, BmCSC1, BmCSC2, BmCGHP, BmCJX, BmCYY and BmCan, which had strong potential pathogenicity. The third group included BmJan, BmK1, BmK2 and BmH which were zero both in mortality rate and RHS index. The duration of life of black pine seedling was the shortest with BmFr population inoculation. The result of treatment with PEG and drought after inoculation with B. mucronatus indicated that drought-stress conditin could significantly increase mortality rate of the seedlings.
