IMPACT OF HOST PLANT XYLEM FLUID ON XYLELLA FASTIDIOSA MULTIPLICATION, AGGREGATION, AND ATTACHMENT

• Author(s): Cooksey, Donald; Toscano, Nick; Bi, Jian; Dumenyo, Korsi; Martinez, Rufina;
• Abstract: Research in Temecula Valley indicated that the proximity of citrus groves to vineyards has influenced the incidence and severity of Pierces disease (PD), Xylella fastidiosa (Xf), in grapes. Although the glassy-winged sharpshooter (GWSS) feeds on and moves back and forth between Temecula citrus groves and vineyards, there are no visible Xylella fastidiosa (Xf) symptoms in the citrus. This implies that citrus trees are resistant or tolerant to the Xf but may be a reservoir to harbor the pathogen for GWSS acquisition while grape vines are susceptible. We investigated the mechanisms of host plant resistance/susceptibility by examining the impact of xylem fluid of grapefruit, orange, lemon and grape on Xf multiplication, aggregation and attachment as well as the related xylem fluid chemistry. Our laboratory experiments revealed that xylem fluid of grapefruit, orange and lemon caused an aggregation of Temecula PD cells to form large white clumps while grape xylem fluid did not cause visible clumping, but created a visible thick biofilm. The numbers of Xf cells in grapefruit xylem fluid treatment were significantly higher at 6, 8 and 9 days after culture compared with those in grape xylem fluid treatment. The numbers of Xf cells in orange or lemon xylem fluid tests were generally lower than those in grape xylem fluid treatment. Citrus xylem fluid significantly inhibited Xf biofilm formation compared to grape xylem fluid. The content of total amino acids in grape xylem fluid was near 9-fold higher than that in grapefruit xylem fluid. Sugar contents were 1.4- to 5.5-fold higher in grape xylem fluid than those in grapefruit xylem fluid. Peroxidase and total thiol levels were also higher in grape xylem fluid than in citrus xylem fluid. Our results indicate that the differences between citrus and grape plants in their responses to Xylella may be due to differences in their xylem fluid chemistry.
• Publication Date: Dec 2004
• Journal: 2004 Pierce's Disease Research Symposium