VIEW ARTICLE

Research.

Harvested Grape Clusters as Inoculum for Pierce's Disease. ALEXANDER H. PURCELL, Department of Environmental Science, Policy and Management, University of California, Berkeley 94720-3112. STUART SAUNDERS, Department of Environmental Science, Policy and Management, University of California, Berkeley 94720-3112. Plant Dis. 79:190-192. Accepted for publication 21 October 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0190.

Harvested fruit clusters from grapevines with Pierce's disease (PD) did not serve as sources from which an efficient insect vector (the blue-green sharpshooter, Graphocephala atropunctata) acquired the causal bacterium Xylella fastidiosa. Sharpshooters fed for 6 hr on fruit clusters harvested from PD-infected vines, then were tested twice for X. fastidiosa by exposure to healthy grapevines. Clusters were tested as possible sources 1,7, 14, and 21 days (stored at 4 C) after being harvested from vines confirmed as having PD. None of 420 surviving blue-green sharpshooters or 84 green sharpshooters (Draeculacephala minerva) from all tests trans-mitted the bacterium to grape, but 88% of 49 blue-green sharpshooters and 24% of 37 green sharpshooters surviving from these tests and then given a 6-hr access on diseased grapevines subsequently transmitted X. fastidiosa to grape. Isolations of X. fastidiosa from cluster stems and rachises were successful in only 5 of 24 samples I day after harvest. Concentrations of X. fastidiosa isolated from stems of diseased clusters were about 10-100 times lower than typical concentrations in grape petioles or leaf veins, decreased each week, and were not recovered after storage for .1 wk. Post-harvest fumigation with sulfur dioxide did not affect rates of recovery of X. fastidiosa from grape cluster stems.