Influence of Phony Disease of Peach on Stem Hydraulic Conductivity and Leaf Xylem Pressure Potential

Stem hydraulic conductivity of peach [ Prunus persica (L.) Batsch] was lower in trees with phony disease than in healthy trees. This lower conductivity occurred in 1- to 4-year stems, in five cultivars, in two pruning systems, and from June through October. Leaf xylem pressure potential was lower in trees with phony disease than in healthy trees in each of the five cultivars tested and from June through September. The reduction in pressure potential in diseased trees exceeded any variations in pressure potential with cultivar or month. The area of functional xylem stained by dye was visibly smaller in stems from diseased trees than in healthy trees. These results were all consistent with the theory that symptoms of phony disease of peach are caused by xylem blockage.