THE DEVELOPMENT OF PIERCES DISEASE IN XYLEM: THE ROLES OF VESSEL CAVITATION, CELL WALL METABOLISM AND VESSEL OCCLUSION

• Author(s): Labavitch, John; Matthews, Mark; Rost, Thomas; Greve, Carl; Kirkpatrick, Bruce; Price, Neil;
• Abstract: This proposal is directed toward discovering the plant responses to infection that are fundamental to the progression of Pierces Disease (PD) in grapevine. The disease is caused by the growth of the bacterium Xylella fastidiosa (Xf) in the xylem vessels of stems, petioles and leaf blades. The disease progresses rapidly, causing severe water deficits in infected shoots and vine deathoften within two years. However the progression of the disease and the mechanism(s) by which the disease produces water deficits and death in infected tissues have not been well established. The prevailing notion is that vessels become occluded with bacteria or products of metabolism. However, it is unclear how the bacterium moves among vessels, whether vessels cavitate upon introduction of the bacterium by the insect vector or during artificial inoculation, and whether the bacterium must enter vessels in order to cause disease symptoms. The bacterium is reported to be larger than the openings in pit pore membranes. Thus, it is likely that cell wall digestion is necessary for movement of the bacteria through the vine. This digestion may be a key component of disease progression. Based on work that we have done (VanderMolen et al., 1983) with the Fusarium oxysporum vascular wilt pathogen that also causes blockage of its plant hosts vascular system, we anticipate a linkage between cell wall metabolism, xylem occlusion, vine water stress and leaf abscission. If the disease develops in a manner similar to fusarium wilt, the plant may respond to oligosaccharide signals (Melotto et al., 1994; Ryan and Farmer, 1991) produced upon digestion of its own cell walls and, consequently, vessels that have not been infected with bacteria may nevertheless become occluded. Therefore the occluding material could be of grapevine origin and component of the plant defense responses to infection. There also is reason to suspect that each vessel cavitates upon bacterial entry, rendering the vessel unable to transport water (Schultz and Matthews, 1986 and 1993; Zimmerman, 1983). Thus cavitation may be the fundamental cause of impaired water transport and leaf death. The proposed work will establish whether the vessels become occluded with material of bacterial or Vitis origin. It will also determine the role of vessel occlusion and cavitation on the progression of PD.
• Publication Date: Dec 2001
• Journal: 2001 Pierce's Disease Research Symposium