アカマツ (Pinus densiflora Sieb. et Zucc) の生態生理学的特性とマツ材線虫病発現の関係

Aerial photographs taken in the southern part of Okayama Prefecture, western Japan, were analyzed and a tree census was conducted for elucidating the relationship between the incident of pine wilt disease and site conditions. Pine wilt damage tended to be less in areas with dry conditions, such as the upper part of a slope and granite rock areas. It was suggested that the drought resistance of pine trees, caused by longterm water stress, was thought to be one of the important factors in resistance to pine wilt disease. Therefore, we examined the charactreristics of water relations of pinus densiflora Sieb. et Zucc. growing in different soil drying and avoided losing water because of the decrease in the leaf pressure potential derived from the high-elastic cell walls and because of the increase in the hydraulic resistance of the branch. Moreover, the P.densiflora under chronic water stress had a high capacity for photosynthesis. The physiological activity of P.densiflora under chronic water stress stayed high even after the inoculation by nematode. It was suggested that P. deinsiflora growing under longterm water stress could resist the influence of the extensive water deficit caused by the shortage of precipitation and by pine wilt disease, and could delay the development of pine wilt disease owing to the drought resistance.