Nine-month persistence of Bursaphelenchus xylophilus in living Abies sachalinensis and Picea jezoensis seedlings and nematode reproduction in stem sections

Bursaphelenchus xylophilus causes pine wilt disease in susceptible pine species. To determine whether B. xylophilus persists in forests containing Abies sachalinensis and Picea jezoensis, we performed inoculation experiments using ten or 15 seedlings of A. sachalinensis, P. jezoensis, Pinus densiflora and P. thunbergii. Inoculation of 15 000 B. xylophilus caused 20 and 7% mortality in A. sachalinensis and P. jezoensis seedlings, respectively, in the nursery, indicating low susceptibility of A. sachalinensis and a lack of susceptibility of P. jezoensis. By contrast, B. xylophilus caused 40 and 70% mortality in P. densiflora and P. thunbergii, respectively. Bursaphelenchus xylophilus was recovered at extremely low densities from stems of externally asymptomatic seedlings of the first two tree species 9.5 months after inoculation. Inoculation of B. xylophilus on excised stem sections of A. sachalinensis and P. jezoensis seedlings showed a greater increase in population density in the bark than xylem after 3 weeks, whereas that on P. densiflora stem sections showed no difference in nematode density between the two tissues. The results suggest that B. xylophilus may persist in forests containing A. sachalinensis and P. jezoensis, when there are insect vectors with affinity for the nematode.