|A scientific and community Internet resource on plant diseases caused by the bacterium Xylella fastidiosa|
Introduction to Pierce's Disease
Pierce's disease (PD), a lethal disease of grapevine, is caused by the bacterium Xylella fastidiosa and is spread by certain kinds of leafhoppers known as sharpshooters. Pierce's disease is only known from North America through Central America and has been reported from some parts of northwestern South America. It is present in some California vineyards every year, with the most dramatic losses occuring in the Napa Valley and in parts of the San Joaquin Valley. During severe epidemics, losses to PD may require major replanting. In Florida and other southeastern states, PD has precluded commercial production of European varieties, but some muscadine grapes and hybrids of American wild grape species with European grapes (Vitis vinifera) are tolerant or resistant to PD.
Pierce's disease, named after N.B. Pierce, seems to be restricted to portions of North America with mild winters. The disease is less prevalent where winter temperatures are colder, such as at higher altitudes, farther inland from ocean influences, and at more northern latitudes. It has been found in all southern states that raise grapes commercially; from Florida to California, and in Mexico and Central America. In the southeastern states, from Florida through Texas, PD is the single most formidable obstacle to the growing of European-type (Vinifera) grapes. Since the mid-1970s, many other strains of Xylella fastidiosa have been discovered, and almost all of these cause leaf scorching of woody perennials such as American elm, maple, mulberry, or plum. In some plants, such as peach and alfalfa, the bacterium slows and stunts plant's growth.
Xylella also causes other diseases in other plants and regions.
|The first evidence of PD infection usually is a drying or "scorching" of leaves (see picture on top of page). The leaves become slightly yellowed (chlorotic) along the margins before drying, or the outer leaf may dry suddenly while still green. Typically, the leaf dries progressively over a period of days to weeks, leaving a series of concentric zones of discolored and dead tissue. About mid-growing season, when foliar scorching begins, some or all of the fruit clusters may wilt and dry up. "Scorched" leaves detach from the distal end of the petiole (leaf stem) rather than from the base of the petiole, leaving the bare petioles attached to canes, often well after normal leaf fall. The bark on affected canes often matures unevenly, leaving islands of mature (brown) bark surrounded by immature (green) bark or the reverse.|
Summer and Fall Symptoms
Xylella fastidiosa bacteria
|One of the key features of grape strains of X. fastidiosa is that grape strains infect a wide range of plant species (Freitag 1951). Recent studies (Hill and Purcell 1995) have shown that the fate of X. fastidiosa can vary greatly from one plant species to another. The bacteria can move internally from cell to cell in blackberry as in grape, but not within California mugwort. All of these plants are important breeding plants of the blue-green sharpshooter in Northern California.|
|Multiplication of Xylella fastidiosa in four plant species|