Pierce's Disease of Grapevines: Indentifying The Primary Vectors In The Southeastern United States

Abstract

In the past 10 years the winegrape industry in the Southeastern United States has experienced rapid growth. However, further expansion may be inhibited by Pierce's disease (PD), caused by the bacterium Xylella fastidiosa that is transmitted from reservoir hosts to grapevines by sharpshooters and spittlebugs. Epidemiological studies were conducted to identify the primary vectors of X. fastidiosa to grapes in the Southeast by surveying sharpshooter populations in the eastern Piedmont and Coastal Plain of North Carolina where PD is most threatening, identifying potential sharpshooter vectors by PCR assays, conducting greenhouse experiments with potential vectors to determine transmission ability, and performing phylogenetic analyses of X. fastidiosa PCR products to provide information on what populations of X. fastidiosa sharpshooters in NC are carrying. In 2004 and 2005, leafhoppers were trapped in three vineyards in the eastern Piedmont and one vineyard in the northeastern Coastal Plain. Four insects have been identified as most abundant, Oncometopia orbona, Graphocephala versuta, Paraphlepsius irroratus, and Agalliota constricta. Specimens of O. orbona, G. versuta, and P. irroratus were tested for the presence of X. fastidiosa using a vacuum extraction method and nested PCR. Over the two seasons 27% of the O. orbona, 24% of the G. versuta, and 33% of the P. irroratus trapped were positive for X. fastidiosa. Transmission experiments were conducted with field-caught O. orbona and G. versuta. One hundred sixty-six vines used in transmission experiments were assayed for the presence of X. fastidiosa by ELISA. Bacterial DNA from an additional sample (n = 6) of symptomatic plants was subjected to two-step PCR to confirm ELISA results. Data indicate both G.versuta and O.orbona transmit X. fastidiosa to grape. Phylogenetic analysis of X. fastidiosa DNA from insects and sequences obtained in silico using Neighbor-Joining of 1000 bootstraps resulted in one most parsimonious tree with three populations grouping by host. SNAP workbench analyses collapsed sequences into to 12 haplotypes and Hudson's ranked Z statistic showed no population subdivision between insect hosts.