Abstract
The relationship between hydraulic conductivity in the xylem and the water status in seven-year-old Japanese black pines(Pinus thunbergii PARL.), which were inoculated with pine-wood nematodes (Bursaphelenchus xylophilus (STEINER et BUHRER) NICKLE) was studied. The water status was determined by measurement of the base xylem pressure potential (BP), and the diurnal trends of the xylem pressure potential (P) and sap flow. The pine trees which were attacked by pine wilt disease exhibited four distinct physiological changes in water status. Inoculated trees also showed an increase in resistance to water flow and a decrease in water status with the advancement of the disease. The increase in resistance to water flow was due to the aspiration of bordered pits resulting from cavitation in xylem water columns. Cavitation seemed to be related to the alteration of metabolism in living cells adjacent to the tracheids. The changes, such as the aspiration of bordered pits, the decrease in oleoresin exudation, and the degeneration of parenchyma cells often occurred beyond the region infected with the nematodes.
