Differentiation and Analysis of Xylella fastidiosa Subspecies fastidiosa Cultures Isolated from a Single Texas Vineyard using Simple Sequence Repeat Markers

Abstract

Xylella fastidiosa subspecies fastidiosa is the causative agent of Pierce’s disease of grape and has caused significant crop stress and loss in vineyards throughout Texas. While multiple techniques are available to identify subspecies of X. fastidiosa, only simple sequence repeat markers can be used for the differentiation of isolates within individual subspecies. In this research, SSR markers were utilized to demonstrate the diversity of subsp. fastidiosa isolates from within a single vineyard. The distributions of strains defined within subsp. fastidiosa were also compared to epidemiological data to clarify any relationships.

Initial results from isolation attempts indicate disease severity to have the largest impact on the success of isolation attempts with 7% of samples rated as ‘Healthy’ and 83% of samples rated as ‘Advanced’ producing successful isolations. A conventional PCR protocol employing 5 SSR markers was used to generate banding profiles for 97 isolates collected from 7 grape varieties planted in 5 blocks throughout a single Texas vineyard. SPSS statistical program was used to execute a hierarchical cluster analysis to produce a dendrogram which grouped isolates into 3 strain groups with 7% or 15% dissimilarity. Of the 3 epidemiological factors analyzed, the distribution of strains showed significant dependence on grape variety while having no dependence on disease severity or location within the vineyard.