FATE OF XYLELLA FASTIDIOSA IN ALTERNATE HOSTS

• Author(s): Purcell, Alexander; Hashim, Jennifer;
• Abstract: This project investigated the fate of the Pierces disease bacterium Xylella fastidiosa (Xf) in alternate hosts from which sharpshooters might acquire Xf by feeding. We identified additional bacterial hosts among vineyard weeds, cover crops, field crops and adjacent vegetation common to vineyards in Californias San Joaquin Valley. Field studies conducted at the Kern County Agricultural Center in Bakersfield tested the survival of Xf in field conditions for five weed and cover crop species known to be systemic hosts of Xf. The rapid and striking emergence of Pierces disease of grape in the General Beale Road project area in Bakersfield during summer 2001 showed the damage that can be done by the glassy-winged sharpshooter (GWSS). Identification and eradication of plants that are bacterial hosts is important where the insect vector has large populations and feeds on many different plants. Xf survives and multiplies in an unusually large number of plants (Freitag 1951; Hopkins 1988), and sharpshooters collected distant from agricultural habitats can be infectious with Xf (Freitag and Frazier 1954). Previous studies of Xf in four plant species established that Xf multiplies in plants at the inoculation site but moves systemically within the plant in only some plant species (Hill and Purcell 1995b). Lab and field studies of Xf in 33 species of riparian plants commonly found in Napa Valley revealed that most plants were propagative but non-systemic hosts of the bacterium and suggested that Xylella eventually disappears from non-systemic hosts (Purcell and Saunders 1999). Research during 2000 and 2001 (funded by Kern-Tulare Glassy-winged Sharpshooter-Pierces Disease Task Force), identified 7 species of weeds as systemic high- and mid-population hosts of Xf and that 12 other weed species were infrequently infected, supported low Xf populations, or had limited bacterial movement beyond the site of insect feeding. We tested 13 additional plant species as hosts of Xf this year. Recent studies of the effects of temperature on Xf growth in culture or in grapevines indicated that Xf slowly dies instead of multiplying at temperatures below 10oC or above 34oC (Feil and Purcell 2001). To determine how well field plants support the growth of Xf during winter and summer, we followed the population changes of Xf in systemic weed or cover crop hosts of Xf grown in Kern County in a protective cage (to exclude vector transmission) in two cool season and two warm season trials.
• Publication Date: Dec 2002
• Journal: 2002 Pierce's Disease Research Symposium