Grapevine susceptibility to Pierce's disease II: Progression of anatomical symptoms.

摘要

The progression of anatomical symptoms of Pierce's disease in susceptible Vitis vinifera cv. Chardonnay grapevines was studied over a time course following controlled inoculation of Y-shaped, two-shooted plants with Xylella fastidiosa. Leaf, petiole and stem tissue samples were collected from inoculated and non-inoculated shoots at 10, 14 and 18 weeks following inoculation. After 10 weeks, leaf necrosis was visible in the inoculated shoots. Leaf and petiole xylem was predominantly occluded with gums and bacteria, whereas stem xylem was occluded almost exclusively with tyloses. After 14 weeks, bacteria and gums were found in non-inoculated shoots, but tyloses were absent from these stem tissues. At 18 weeks, tylose development was observed in the xylem in stems of non-inoculated shoots. Consequently, basipetal movement of bacteria occurred from the inoculated shoot into a non-inoculated shoot. The results indicate that there is a predictable initial sequence of symptoms within infected shoots: gum and bacterial accumulation in leaves and petioles followed by tylose formation in stem tissue. This pattern is repeated with the colonization of new shoots, eventually creating a systemic presence of the disease.