Abstract
In the preceding papers, the authors showed that the genuine pathogen of the pine wilt disease is the phenylacetic acid-producing bacteria accompanying the pine wood nematodes. However, the difference in pathogenicity between nematode isolates (OKD-1 and OKD-3) could not be explained solely by the accompanying bacteria because weakly pathogenic isolate OKD-1 also was accompanied by the bacteria. The facts that the pine wilt disease is prevented by injection of a nervous action inhibitor to the pine trunk made the authors suppose that inherent mobility of the isolates is also important for expressing pathogenicity. In this paper, the authors have compared the mobility of the nematodes in mycelia of Botrytis cinerea grown on crushed barley grains in a microtube among a weakly pathogenic isolate OKD-1, a strongly pathogenic isolate OKD-3, and its bacteria-free nematode OKD-3-BF. The strongly pathogenic isolates OKD-3 showed larger mobility irrespective of accompanying bacteria than the weakly pathogenic isolate OKD-1. This finding suggests that the different pathogenicity of the two isolates is explained by the difference in mobility between these isolates.
