Evaluating the Effect of Rootstock on the Susceptibility of Chardonnay to Pierce's Disease Expression.

Pierce's Disease is a lethal disease of grapevine (Vitis spp.) that limits viticulture in the southern parts of North America. It is considered to be the primary reason for the failure of both the European bunch grape (V. vinifera L.) and the American bunch grape (V. labrusca L.) in the southeastern United States (Hewitt 1958, Hopkins 1977, Loomis 1958). It is also a persistent threat to the California viticulture industry in which cyclical epidemics have destroyed vineyards and have caused severe economic losses to grape growers (Hopkins and Adlerz 1988, Hewitt 1942, Pierce 1892). The disease, which is transmitted by xylem-feeding insects such as sharpshooters and spittle bugs (Hewitt 1942, Hewitt 1945), was thought to be viral in origin until it was described as a rickettsia-like bacterium inhabiting the xylem (Auger et al. 1974, Goheen et al. 1973, Hopkins and Mollenhauer 1973). The casual agent is now described as a gram-negative bacterium related to Xanthomonas species, but belonging to a new genus and species Xylella fastidiosa (Xf) (Wells et al. 1987). Newton B. Pierce was the first viticulturist to document and characterize the disease he referred to as `The California Vine Disease' in an 1892 U.S. Department of Agriculture Bulletin. The disease subsequently became known as Pierce's Disease (PD) in honor of his early and extensive research of the disease. In order to trace the origins of the disease in California, Pierce documented the history of vine cultivation in California. He speculated that the first introductions of V. vinifera, the European bunch grape commonly used for wine, table grape, and raisin production, occurred around the middle of the 18th century when Spanish missionaries from Baja and Mexico brought V. vinifera `Mission' to the southern California region. He also noted that Mission and other cultivars were grown successfully for many years prior to the first outbreak of the California Vine Disease. The first records of California vine decline due to PD date in the 1880's. The discovery and characterization of the disease in the Santa Ana Valley in 1884 was the beginning of an epidemic that spread throughout much of southern California and forced the viticulture industry to relocate to other parts of the state (Pierce 1892). By 1895, PD was responsible for destroying more than 30,000 acres of productive vineyards in the southern California area. The disease was reported at this time in the Napa and Sacramento Valleys, but it did not become epidemic in these areas until later (Hewitt et al. 1942). Hewitt et al. (1942) documented a second major epidemic of PD that took place in the San Joaquin Valley between 1937-1944 (Winkler et al. 1974). Subsequently, cyclical epidemics of PD have threatened the grape industry in the coastal valleys of northern California, in the Central Valley where most of the viticulture industry is located, and in Temecula Valley (Goheen et al. 1973). PD is widely distributed in the United States Gulf Coastal Plain area, and it is the principal factor responsible for the failure of V. vinifera grapes in the southeastern United States (Hewitt 1958). Several Vitis species, indigenous to this region, resist or tolerate Xf, leading to speculation that this is PD's region of origin. PD may have been introduced to California in grape wood from this region (Hewitt 1958). It is speculated that the disease may have arrived with shipments of American Vitis species that were to be tested and used for their phylloxera resistance or tolerance. The phylloxera epidemic in California directly preceeded the discoveries of PD. However, Xf has subsequently been recovered from a variety of host plants, over 100 species, 70 genera, and 27 families (Frietag 1951, Hopkins and Adlerz 1988, Purcell and Saunders 1999, Raju et al. 1983, Raju et al. 1980). The disease agent could have been introduced and reintroduced several times at different localities in California, but its widespread presence in plants native to California suggests that it has been present in the state for a very long time. In addition, there are a variety of native sharpshooter insects in California that can spread Xf. Currently, PD continues to cause large economic losses to grape growers, even in viticultural regions that are not experiencing epidemics. The North Coast PD Task Force estimated that growers in Napa and Sonoma counties collectively lost over 33 million dollars to PD since 1994 (http://danr.ucop.edu/news/speeches/PDintroduction.html). In addition to these chronically infected areas, a recent PD outbreak that began in Temecula Valley has the potential to spread at alarming rates due to the introduction of a new vector, Homalodisca coagulata, the glassy-winged sharpshooter (Sorensen and Gill 1996). Management strategies have thus far proved to be only marginally effective in lessening the severity of PD. The investigation of alternate strategies is necessary and on-going.