Inhibition of Bursaphelenchus xylophilus migration at the nodes of pinus thunbergii

The effect of the nodes and their characteristics in Pinus thunbergii seedlings on the migration of the pinewood nematode, Bursaphelenchus xylophilus, were examined. We counted the number of nematodes that passed through stem-cuttings with nodes having different numbers of whorled branches (WBs) and those without nodes. Additionally, we studied the anatomical characteristics of the cortical resin canals CRCs at the nodes. We inoculated nematodes into seedlings of P. thunbergii to investigate the relationship between the number of WBs and symptom development. Fewer nematodes passed through the stem-cuttings with nodes than through the stem-cuttings without nodes, and these numbers decreased as the number of WBs increased. These results indicate that the migration of nematodes through the stem-cutting via the nodes is inhibited and the effect enhanced when WBs are more. The CRCs near the nodes were connected, and they curved at the base of the whorled branches. The number and size of the CRCs in the cross-section of nodes were smaller than those of CRCs in the cross-section of the stem away from the nodes. Such CRCs structures were promising as a factor for the inhibited the migration of the nematodes. The beginning of the foliage discoloration delayed in the seedlings with large number of WBs comparing to those with fewer WBs. This suggests that the inhibition of nematode migration at the nodes with many WBs may lead to the delay of the symptom development.