Response of Resistant, Tolerant, and Susceptible Grapevine Tissues to Invasion by the Pierce's Disease Bacterium,Xylella fastidiosa

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Abstract
Microtechniques were used to quantify occlusion of leaf veins of grapevines inoculated with Xylella fastidiosa. Bacteria and pectins were responsible for most occlusions in xylem vessels of inoculated Vitis vinifera ''French Colombard'' (susceptible to Pierce''s disease) and V. rotundifolia ''Carlos'' (tolerant) and ''Noble'' (resistant). The average percentage of vessels in leaf veins colonized by the bacterium and occluded by pectins was greatest in French Colombard. Occlusion by tyloses occurred to a similar extent among all cultivars. The average percentage of vessels occluded by gums and tannins was greatest in Noble, and similar between French Colombard and Carlos. The majority of pectins, bacteria, and tyloses occluded leaf vein vessels partially. In general, fewer occlusions were observed in buffer-inoculated (control) plants than in pathogen-inoculated plants.