Abstract
Pinus thunbergii (susceptible to pine wilt) and P. taeda (resistant species) seedlings were inoculated with one of the following three Bursaphelenchus isolates; one pathogenic (B. xylophilus) and two nonpathogenic (B. xylophilus and B. mucronatus) isolates. The effect of water extracts from the nematode-inoculated seedlings on the nematodes' movement was tested in relation to the dynamic resistance induced in the host. In every water extract from seedlings of either pine species, the movement of all isolates was inhibited, however, the inhibition to pathogenic isolates diminished later on. The results indicate that some substance(s) responsible for the inhibition of nematode movement was produced in the stems of the inoculated pine seedlings. The substance was denatured as the disease progressed, and movement of the pathogenic isolate became free from inhibition, while that of two nonpathogenic isolated did not. Regardless of the nematode isolate inoculated, extracts from P. taeda were somewhat more suppressive to nematode movement than those from P. thunbergii, although the differential manner of inhibition against the three nematode isolates was similar. Nematode migration and proliferation in stems of the seedlings, decline of water content and resin exudation of the stems were confirmed only when susceptible pine seedlings were inoculated with the pathogenic isolate.
