MECHANISMS OF PIERCE'S DISEASE TRANSMISSION IN GRAPEVINES: THE XYLEM PATHWAYS AND MOVEMENT OF XYLELLA FASTIDIOSA. PROGRESS REPORT NUMBER TWO: GREEN ISLANDS AND MATCHSTICKS

• Author(s): Matthews, Mark; Rost, Thomas; Stevenson, Joshua;
• Abstract: During this period our focus was the comparative xylem anatomy of a resistant species, Muscadinia rotundifolia cv Cowart and a susceptible species, Vitis vinifera cv Chardonnay. When infected by Xylella fastidosa both species produced tyloses (parenchyma ingrowths into tracheary elements) and gums; M. rotundifolia tended to have fewer tyloses. The resistant species also had narrower vessels, but otherwise xylem anatomy was similar to V. vinifera. Fluorescently tagged beads were loaded into both species. Beads traveled through the stem xylem in both, but did not move into petioles in these experiments. Tyloses were first apparent 24 hours after pruning in both species and most vessels were blocked in both after eight days of pruning. This suggests that the mechanism to form tyloses in both species is similar, although the resistant species tended to show fewer tyloses in response to Xf. Two symptoms, green islands and matchsticks are reported in this study. Green islands formed as a result of incomplete initiation of the phellogen. In regions of the stem where a phellogen and subsequent periderm arose, immediately exterior tissue was cut off, causing it to brown. In regions of the stem where no periderm is formed, the exterior tissues remained green. Consequently, the stem is mottled with both green living epidermis and brown dying epidermis as determined by the presence or absence of an underlying periderm. Matchsticks formed when the leaf lamina separated from the petiole, and the petiole remained attached to the stem. Lamina broke off from the petioles consistently in a fracture zone where xylem from the petiole anastomoses into the five major veins of the leaf. No separation layer was found to explain this pseudoabscission.
• Publication Date: Dec 2004
• Journal: 2004 Pierce's Disease Research Symposium