|Islam, Md Sajedul|
|Walker, M. Andrew|
Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 11/30/2010
Publication Date: 12/6/2010
Citation: Lin, H., Morano, L., Islam, M., Civerolo, E.L., Walker, M. 2010. Genetic structure of Xylella fastidiosa within two important grape growing regions in the United States: California and Texas. CDFA Pierce's Disease Control Program Research Symposium, December 15-17, 2010, San Diego, California. p.112-117. Interpretive Summary: Xylella fastidiosa (Xf) causes Pierce’s disease in grapevine. In this study, we report genetic diversity and population genetic structure of grape Xf strains between two important grape growing regions in the United States, California and Texas. Using multiple sets of molecular markers, differences were found in both in California and Texas populations. Further genetic analyses indicate local level geographical structure within California populations; significant genetic differentiation was found among isolates from Mendocino, Sonoma, Napa, Kern and Riverside counties. On the other hand, no geographic association was observed in grape or non-grape strains in Texas. Our data suggests that Xf populations in California and Texas may be originally derived from two different origins regardless of host. However, the discovery of some Texas alleles in California may reflect recent introduction of Texas strains into California, possibly through movement of the insect vector, glassy-winged sharpshooter (Homalodisca vitripennis), into Southern California (Temecula region).
Technical Abstract: Xylella fastidiosa (Xf) causes Pierce’s disease in grapevine. Here, we report on the genetic diversity and population genetic structure of grape Xf strains between two important grape growing regions in the United States, California and Texas. Using multilocus microsatellite markers, high genetic diversity of Xf was observed in California and Texas populations with a grand mean haploid genetic diversity of 0.427. Partitioning of genetic diversity (heterozygosity) across all 13 microsatellites (SSR) loci found high values within the two grape growing regions with 0.460 within California isolates, and 0.452 within Texas isolates. Cluster analysis of Nei’s genetic distances and hierarchical analysis of molecular variance separated Californian isolates from Texan isolates regardless of host, and also showed significant genetic differentiation between the isolates collected from these two broad geographic regions. Pairwise (FST) comparisons of local level geographical structure within Californian populations found significant genetic differentiation among isolates collected from Mendocino, Sonoma, Napa, Kern and Riverside counties. However, some populations from the most genetically diverse Napa County differed from each other, and shared genetic similarities with Kern or Riverside counties. On the other hand, no geographic association was observed with grape or non-grape strains in Texas, although host-associated structure was observed. Bayesian modeling using STRUCTURE software indicated that Xf in California and Texas may be derived from different origins regardless of host. However, identification of strains with up to 17% Texan origin in some California counties lead us to hypothesize the introduction of Texan strains into California. This introduction seems to have initiated in southern California (Temecula region) followed by range expansion throughout different regions in California.