Rickettsia-like bacteria, implicated as the casual agent of Pierce’s disease, were easily observed by electron microscopy in the xylem of muscadine grape (Vitis rotundifolia Michx.) with symptoms of Pierce’s disease. The symptoms included severe stunt, marginal leaf burn, and dieback. The bacterium was observed only in the tracheary elements of the xylem.
Differences in levels of tolerance to Pierce’s disease were found in muscadine cultivars and breeding selections. Muscadine cultivars and selections developed at Experiment, GA were generally more tolerant to the disease than those developed at Meridian, MS or Raleigh, NC, however, there were some highly tolerant cultivars from all 3 locations. Cultivars from MS were much more tolerant to the disease than were selections from that location which were never considered acceptable for release to commercial growers.