Abstract
The native Japanese pines Pinus thunbergii and P. densiflora are susceptible to pine wilt disease caused by the pinewood nematode, Bursaphelenchus xylophilus, while P. taeda is more resistant than these native Japanese species. We studied symptom development in these three pines after inoculation with a virulent isolate of the pinewood nematode. Nematode populations increased throughout seedlings of both P. thunbergii and P. densiflora soon after ray parenchyma cells showed drastic histochemical changes, i.e. accumulation of catechol tannin, spread of lipids over the whole cell, and leakage of cell contents. However, in P. taeda seedlings, nematode populations remained low and histological changes occurred only near the inoculation site. These results suggest that drastic cytological changes in ray parenchyma cells may promote symptom development from an early to an advanced stage.
