Retardation of pine wilt disease symptom development in Japanese black pine seedlings exposed to simulated acid rain and inoculated withBursaphelenchus xylophilus

Three- or 4-year-old Japanese black pine seedlings were exposed to simulated acid rain (SAR) at pH 3 for two months, then inoculated with a virulent isolate (S 10) of pinewood nematodes. The experiments were repeated three times in 1996–1998. The exposure to SAR killed no seedlings, and retarded the development of disease symptoms in the seedlings inoculated with nematodes. In the experiments in 1996 and 1997, however, cessation of resin exudation, and primary decrease in the xylem conductivity occurred earlier in the seedlings exposed to SAR than in those exposed to tap water as a control. These results imply that acid rain at pH 3 influenced an increase in some resistance of Japanese black pine seedlings to pinewood nematode, and that this improved resistance could potentially overcome damage caused by acid rain. The exposure to SAR did not have any significant effect on the water relations of the seedlings itself, suggesting that retardation of the symptom development after the exposure to SAR could not be attributed to the improvement in the water relations. This work was supported in part by a Grants-in-Aid for Scientific Research from the Japan Forest Technical Association (JAFTA).