Pathogenicity and attraction to host extracts of Canadian pinewood nematodes: studies with Scots pine, western larch, and black spruce seedlings

Abstract

Two isolates of the pinewood nematode, Bursaphelenchusxylophilus (Steiner and 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, Pinussylvestris L., western larch, Larixoccidentalis Nutt., and black spruce, Piceamariana (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 tannin 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 conifers: the Japanese isolate 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, ethyl 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.