Monday, 15 November 2004

Environmental variables that contribute to the severity of Pierce’s disease in California grapevines

Christopher J. Boisseranc, and Michael J. Costello, California Polytechnic State University, Department of Horticulture & Crop Science, San Luis Obispo, CA

Pierce’s Disease of grapevine is influenced by the interaction of host plant, disease, and insect vector, and it is suggested that environmental factors such as adjacent vegetation, proximity to riparian habitats, soil chemistry, soil biology, plant water status, and climate may contribute to disease severity. Xylella fastidiosa, the bacterium responsible for Pierce’s Disease, is a gram-negative fastidious bacterium that is an obligate parasite requiring host xylem tissue to complete its lifecycle. With the introduction of a new invasive sharpshooter species, the Glassy-winged sharpshooter, Homoladisca coagulata, Pierce’s Disease is being dispersed more efficiently than our native sharpshooters have previously, and has led to an outbreak of disease. The bacterium can co-exist within most native plant species as it completes its lifecycle in the non-living xylem tissue of the vegetation. The wine grapevine, Vitis vinifera, cannot co-exist with this bacterium, as it will cause an over accumulation of bacteria thus plugging the xylem elements and starving the plant of nutrients and water. Our goal was to attain a set of environmental variables that contribute to the severity of Pierce’s Disease when studying sites in Northern and Southern California for the 2002 and 2003 growing seasons. Given the multidimensional nature of Pierce’s Disease we used canonical correspondence analysis (CCA) to determine the most influential factors that contribute to the severity of disease expression.

Species 1: Homoptera Cicadellidae Homoladisca coagulata (glassy-winged sharpshooter)
Species 2: Homoptera Cicadellidae Graphocephala atropunctata (blue-green sharpshooter)
Keywords: Pierce's disease

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