PATTERNS OF XYLELLA FASTIDIOSA INFECTION IN PLANTS AND EFFECTS ON ACQUISITION BY INSECT VECTORS

• Author(s): Lindow, Steven; Purcell, Alexander; Wistrom, Christina;
• Abstract: We are studying the effect of host plant tolerance on insect vector acquisition of Xylella fastidiosa (Xf) from plants tolerant, moderately susceptible, and highly susceptible to Xf infection. We are observing Xf population and distribution in tolerant and susceptible plants, and its relationship to xylem anatomy, symptom development, and bacterial acquisition by sharpshooters. Since host plant resistance is an important component in the long-term goal of curing PD, it is important to know how resistant plants affect PD spread in areas permanently infested with sharpshooter vectors. We also address the short-term goal of controlling PD spread by comparing grape cultivars in their ability to provide inoculum for vine-to-vine spread of Pierces disease. Anatomical comparisons of three cultivars, Sylvaner, Cabernet Sauvignon and Pinot Noir showed that all three varieties had similar numbers, lengths and distributions of vessels. The only significant difference was that tolerant Sylvaner had ~ 20 % more rays than the more susceptible Cabernet Sauvignon or Pinot Noir (n = 25, P = 0.01) in canes of similar age, length and diameter. In all four alternate hosts, morning glory (Ipomoea purpurea), mugwort (Artemisia douglasiana), sunflower (Helianthus annuus) and annual bur-sage (Ambrosia acanthicarpa), the longest vessels measured were less than 13 cm long, while in grapes the longest vessels averaged 62 cm. Though alternate hosts had various vascular morphologies and stem lengths, all had shorter vessels than grapes. Blue-green sharpshooters failed to efficiently inoculate wild-type Xf and green fluorescent protein-expressing (GFP) Xf into both grapes and alternate hosts; only one of 44 grapes inoculated with BGSS became infected. In order to generate GFP-Xf infected plants for microscopy, we are mechanically inoculating alternate hosts and grapes. Ongoing work focuses on refining microscopic techniques to visualize small numbers of Xf in plant stems, and generating large numbers of Xf infected grapevines to serve as new sources for sharpshooter bacterial acquisition.
• Publication Date: Dec 2004
• Journal: 2004 Pierce's Disease Research Symposium