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Xylella fastidiosa (Xf) causes diseases in many agricultural, horticultural, and landscape crops, including Pierce's disease (PD) of grapevines. PD has been a serious problem in scattered table, wine and raisin grape growing regions throughout California, as well as in Texas for more than 100 years. In this study, we evaluated the genetic variation in diversity and structure of Xf associated with PD of grapevines in California and Texas using simple sequence repeat (SSR) markers. The analysis revealed a high level of genetic diversity across the populations of Xf isolated from the grapevines from different viticulture locations or counties in California and Texas. Overall genetic diversity of Xf was detected comparatively high in Texas (0.835) than that in California (0.662). Hierarchical analysis of molecular variance (AMOVA) showed a significant genetic structure of Xf population between California and Texas. UPGMA clustering analysis and the Bayesian clustering algorithm using STRUCTURE consistently placed California and Texas Xf populations into two major genetic groups with no clear population structure within each state. [ABSTRACT FROM AUTHOR]

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is the primary insect vector of the xylem-limited plant pathogen Xylella fastidiosa fastidiosa Wells (Xanthomonadales: Xanthomonadaceae), the bacterium that causes Pierce's disease of grape, Vitus sp. Because it is mobile and polyphagous, the glassy-winged sharpshooter is key to Pierce's disease outbreaks in California, Florida, and Texas. Adult age structure and X. fastidiosa foregut infectivity rates of glassy-winged sharpshooter from nine Texas vineyards in summer 2007 were assessed from archived samples. The ages of individuals were determined by measuring the red pigmentation of forewing intersections. Presence or absence of X. fastidiosa was determined in the foregut of pathogen-positive insects by quantitative PCR. Larger amounts of the associated pathogen in insects from two vineyards sampled in 2005 and 2006 were observed. No significant differences in average insect age among vineyards or collection dates were found in those years. However, significant differences in average pathogen load among multiple vineyards and collection dates were observed. [ABSTRACT FROM AUTHOR]