|Islam, Md Sajedul|
Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2012
Publication Date: 5/20/2013
Citation: Lin, H., Islam, M., Morano, L., Groves, R., Bextine, B., Civerolo, E.L., Walker, M. 2013. Genetic variation of Xylella fastidiosa associated with grape vines in two major viticulture regions in the United Sates: California and Texas. Journal of Plant Pathology. 95(2):329-337. Interpretive Summary: Xylella fastidiosa (Xf) causes Pierce’s disease in grapevine. In this study, genetic diversity and population genetic structure of Xf strains isolated from grapes in two improtant grape growing regions in the United States, California and Texas, are described. Using multiple sets of molecular markers, genetic differentiation was found in both California and Texas Xf populations. Further genetic analyses indicated local geographic structure within California populations in which significant genetic differentiation was found among strains collected in Mendocino, Sonoma, Napa, Kern and Riverside counties. In contrast, no geographic association was observed in grape or non-grape strains in Texas. The data suggest that Xf populations in California and Texas may have been originally derived from two different origins/ancestors regardless of host. However, the observation that some California Xf strains shared features of Texas strains suggests that Texas strains may have been recently introduced into California likely through introduction of the glassy-winged sharpshooter(Homalodisca vitripennis), insect vector, in Southern California.
Technical Abstract: Xylella fastidiosa (Xf) causes Pierce’s disease in grapevine. Here, genetic diversity and population structure of grape strains of Xf collected from two important grape growing regions in the United States, California and Texas, is presented. Multilocus simple sequence repeat (SSR) markers revealed high genetic diversity in California and Texas Xf populations with a grand mean haploid genetic diversity of 0.427. Partitioning of genetic diversity (heterozygosity) across 13 SSR loci found high values within the two grape growing regions with 0.460 within Californian strains, and 0.452 within Texas strains. Cluster analysis of Nei’s genetic distances and hierarchical analysis of molecular variance separated California strains from Texas strains regardless of host, and also showed significant genetic differentiation between strains collected from these two broad geographic regions. Pairwise (FST) comparisons of local level geographical structure within California populations found significant genetic differentiation among strains collected from Mendocino, Sonoma, Napa, Kern and Riverside counties. Napa County had the most genetically diverse population within California, but shared genetic similarities with both Kern and Riverside counties. In contrast, no geographic association was observed with grape or non-grape strains in Texas, although host-associated structure was observed with these strains. Bayesian modeling using STRUCTURE indicated that Xf in California and Texas may be derived from different origins, regardless of host. However, the observation that some California Xf strains shared features of Texas strains suggests that Texas strains have been recently introduced into California. This introduction seems to have initiated in the Temecula region followed by expansion to various locales within California.