FATE OF XYLELLA FASTIDIOSA IN ALTERNATE HOSTS

• Author(s): Purcell, Alexander; Hashim, Jennifer; Wistrom, Christina;
• Abstract: Investigations of the fate of the Pierces disease bacterium Xylella fastidiosa (Xf) in alternate hosts from which sharpshooters might acquire Xf identified bacterial hosts among vineyard weeds, cover crops, field crops and adjacent vegetation common to vineyards in Californias San Joaquin Valley. Work for the past year focused on completing additional replications of 15 high-priority weeds to compare mechanical and insect vector inoculation efficiencies, and to determine the fate of bacterial populations over a nine-week period after inoculation with Xf. Four things are required for a plant to be a good source of Xylella for vector acquisition: it must be an attractive food host to sharpshooters, develop Xylella infections frequently when fed on by infective insects, allow systemic growth of the bacteria beyond the inoculation site, and support population growth above 1,000,000 cfu of Xf per gram of plant tissue. Although insect survival varied considerably between replications, it averaged 77% on all plants for two days. Ten of the 35 weed species examined were colonized by Xf more than 50% of the time in greenhouse studies when plants were maintained in ideal conditions for bacterial growth. Sixteen species supported Xylella populations above 1,000,000 cfu/g, thirteen had populations between 1,000,000 and 10,000 cfu/g, and three had populations below 10,000 cfu/g. Finally, 13 species had Xf recovery immediately distal to the inoculation site in greater than half of successfully inoculated plants. The plants that had greater than 60% insect survival during inoculation, more than 50% of sites inoculation sites infected in greenhouse tests, that supported bacterial populations of 1,000,000 cfu/g or larger, and had systemic Xf movement beyond the inoculation site in more than half the infected inoculation sites were: black nightshade, common sunflower, annual bur-sage, morning glory, poison hemlock and fava bean.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium