Two isolates of the pinewood nematode, Bursaphelenchus xylophilus (Steiner und Buhrer), from Canada (an r form from Ontario and an m form from Quebec) and one from Japan (an r form) were inoculated into Scots pine, Pinus sylvestris L., western larch, Larix occidentalis Nutt., and black spruce, Picea mariana (Mill.) B.S.P. to determine the pathogenicity of this nematode and to observe changes in its numbers as well as the effect it had on seedling water and tanning content. Attractiveness of water, ethyl ether, and ethyl acetate stem extracts of these conifers to the pinewood nematode was also determined. The r form of the pinewood nematode was pathogenic on all three confers: the Japanese islate killed more Scots pine and the Ontario isolate, more black spruce. The Quebec isolate was as pathogenic as the other two isolates to western larch, weakly pathogenic to black spruce, and nonpathogenic to Scots pine. In general, there was a positive relationship between nematode population buildup and seedling mortality. No clear relationship was found between the water content of seedling stems and changes in nematode populations. Tannin content of stems increased following inoculation with pinewood nematode, but whereas correlation values between tannin content and nematode numbers were positive and significant, they were small. Although all three isolates were attracted to all host extracts, regardless of solvent used, ethly acetate extracts were generally more attractive. The Japanese and Ontario isolates, which originated from pines, showed no particular affinity for Scots pine extracts; however, the Ontario isolate, which was especially attracted to black spruce extracts, was also most pathogenic to black spruce.
