Abstract
For the effective selection of pine wilt disease-resistant Pinus thunbergii trees, we implemented three strong inoculation tests of the seedlings with pine wood nematodes (PWNs). In the first test, we studied the environmental conditions associated with increased mortality after inoculation. The inoculation was performed in a greenhouse under high temperature and the pot-grown seedlings were subjected to moisture stress. Under these conditions, the survival rate following inoculation with 10,000 Shimabara, a highly virulent PWN isolate, was approximately 3%. In the second test, we attempted to increase the mortality by increasing the number of PWNs in an inoculation. When we inoculated seedlings with 10,000 or 20,000 Shimabara, the survival rate following inoculation with 20,000 PWNs was half than that with 10,000 PWNs. The third test examined the association between the increased resistance of undamaged population and their inoculation history. We repeatedly inoculated undamaged seedlings with PWN in subsequent years and selected the undamaged seedlings. The selected populations were inoculated with 20,000 Ka-4, which is another highly virulent PWN isolate. Withering of seedlings with a history of many inoculations progressed slowly, and their survival rates increased. The withering process was in line with the previous reports on resistant P. thunbergii varieties. We concluded that this method is effective for the selection of resistant P. thunbergii.
