Studies on the Resistance of Pine Trees to Pine Wood Nematode, Bursaphelenchus xylophilus

Resistance of 23 pine species and 105 provenances of 5 pine species and 13 tree species of Pinaceae other than Pinus to pine wood nem-atode were determined. The resistance of 23 pine species varied greatly. Pinus taeda, P. banksiana, P. rigida were not infected. The resistance of P. massoniana was relevant to the seedling age, one-yr old seedlings of the pine were infected, but two-yr, four-yr old seedlings and ten-yr old tree were resistant. The resistance of different provenances of one pine species usually were not significant. Almost all of the trees other than Pinus were diseased except Cedrus deodara. Environmental conditions influence the resistance of pine host obviously. Low temperature was not favourable for disease development. The pathogenicities of pine wood nematode populations from different locations and pine species to the same pine species were different, and the difference among the nematode populations from different locations was more remarkable than that among the populations from different pine species in the same location. Inoculum density and pine mortality assume positive correlation. Besides, the resistance of Pinus masso-niana was discussed.