Reservoir Hosts and Vectors of Xylella fastidiosa, Causal Agent of Pierce's Disease of Grapevines, in North Carolina

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Title: Reservoir Hosts and Vectors of Xylella fastidiosa, Causal Agent of Pierce's Disease of Grapevines, in North Carolina
Author: Floyd, Leah Evelyn
Advisors: David Ritchie, Committee Member
George Kennedy, Committee Member
Turner Sutton, Committee Chair
Abstract: Pierce’s disease (PD) of grapevines is caused by the xylem-limited bacterium Xylella fastidiosa (Xf) which is transmitted by leafhoppers and spittlebugs. Leafhopper populations were surveyed in six vineyards across North Carolina’s three geographic regions, in 2006 and 2007. Populations of two phloem-feeders, Agallia spp. and Paraphlepsius irroratus were compared with populations of known PD vectors, Graphocephala versuta and Oncometopia orbona as well as other leafhoppers and planthoppers. G. versuta was the dominant species in the Piedmont and Mountain regions in 2007 and in one Coastal Plain vineyard in 2006. Agallia spp. were most common in the Coastal Plain in 2007, and in the two Mountain and Piedmont vineyards in 2006. The possibility that a phloem-feeder may transmit Xf to grapevines was examined. The clover leafhopper, A. sanguinolenta, a phloem-feeder, did not transmit Xf to grapevines and the bacterium was not detected in its mouthparts using RT-PCR analysis. A reservoir host list of Xf was developed for North Carolina. This was developed using ground vegetation surveys conducted in three vineyards in the spring and fall of 2007-08 to identify and quantify plant species growing on the vineyard floor. Plant samples were collected and tested for the presence of Xf with ELISA and PCR. Fourteen of 40 plant species surveyed tested positive with ELISA and two were confirmed with PCR. Plant hosts of Xf identified in this study that have not been previously reported are: Chamaesyce maculata, Trifolium arvense, hop clover, Trifolium spp., Geranium carolinianum, Oxalis stricta, Festuca sp., Setaria sp., Hordeum pusillum, Poa trivialis and Ranunculus sp. Plant hosts of Xf identified that were previously reported to host PD-strains of the bacterium include: Trifolium repens, Plantago lanceolata, Digitaria sp., and Cynodon dactylon. To further examine the importance of potential groundcovers as reservoir hosts, experiments were conducted to find a groundcover that the known PD vector, Graphocephala spp. does not prefer for feeding. None of the plant species tested were found to be poor reservoir hosts, with regard to G. versuta feeding preference. Additionally, the effect of the presence of fungal endophytes on the survival of G. versuta was investigated. Those present in Festuca rubra spp. rubra and Festuca rubra ssp. commutata did not affect the survival of G. versuta. We recommend removing broadleaf weeds from the vineyard floor, and studies to find a suitable groundcover should be continued.
Date: 2009-04-22
Degree: MS
Discipline: Plant Pathology

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