Xylella fastidiosa

Xylella fastidiosa, a bacterium in the class Gammaproteobacteria, is an important plant pathogen that causes phoney peach disease in the southern United States, Bacterial Leaf Scorch, oleander leaf scorch, and Pierce's disease, and citrus variegated chlorosis disease (CVC) in Brazil.

Pierce's disease

Pierce's disease (PD) was discovered in 1892 by Newton B. Pierce (1856–1916; California's first professional plant pathologist) on grapes in California near Anaheim. The disease is endemic in northern California, being vectored by the blue-green sharpshooter, which only spreads the disease to grapevines that are adjacent to riparian habitats. It became a real threat to California's wine industry when the glassy-winged sharpshooter (GWSS), native to the southeast United States, was discovered in the Temecula Valley in California in 1996. The GWSS spreads PD much more extensively than other vectors do. It triggered a unique effort from growers, administrators, policy makers and researchers to work together in finding a solution for this immense threat. No cure has yet been found,^[1] but the understanding of Xylella fastidiosa and glassy-winged sharpshooter biology has increased much since 2000, when the California Department of Food and Agriculture, in collaboration with different universities, such as University of California, Davis; University of California, Berkeley, and University of California, Riverside, and University of Houston-Downtown started to focus their research on this pest. The research explores the different aspects of the disease propagation from the vector to the host plant and within the host plant, to the impact of the disease on California's economy. All researchers working on Pierce's disease meet annually in San Diego in mid-December to discuss the progress in their field. All proceedings from this symposium can be found on the Pierce's disease website,^[2] developed and managed by the Public Intellectual Property Resource for Agriculture (PIPRA).^[3]

There are no resistant Vitis vinifera varieties, and Chardonnay and Pinot noir are especially sensitive, although muscadine grapes have a natural resistance.^[1] Pierce's disease is presently found in the southeastern United States and Mexico. Also it uas reported by Luis G. Jiménez-Arias in Costa Rica, and Venezuela,^[4] and possibly in other parts of Central and South America. There are isolated hot spots of the disease near creeks in Napa and Sonoma in northern California.^[1]

Currently, work is underway at U.C. Davis to breed PD resistance into Vitis vinifera. The first generation was 50% high quality vinifera genes, the next 75%, the third 87% and the fourth 94%. In the spring of 2007, seedlings that are 94% vinifera were planted.^[5]

When a vine becomes infected, the bacterium causes a gel to form in the xylem tissue of the vine, preventing water from being drawn through the vine. Leaves on vines with Pierce's disease will turn yellow and brown, and eventually drop off the vine. Shoots will also die. After one to five years, the vine itself will die. The proximity of vineyards to citrus orchards compounds the threat, because citrus is not only a host for the sharpshooter eggs, but it is also a popular overwintering site for the insect. Likewise, oleander, a common landscaping plant in California, serves as a reservoir for Xylella.

Highly virulent outbreaks of the disease are being reported on olive trees across the Lecce province, Southern Italy, with hundreds plants already wilting and dying.

Oleander leaf scorch

Nerium oleander infected with Xylella fastidiosa in Phoenix, Arizona

Oleander leaf scorch is a disease of landscape oleanders (Nerium oleander) caused by a strain of X. fastidiosa which has become prevalent in California and Arizona, USA starting in the mid 1990s. This disease is transmitted by a type of leafhopper (insect ) called the Glassy-winged sharpshooter (Homalodisca coagulata).

Genome sequencing

The genome sequencing of X. fastidiosa was realized by a pool of over 30 research labs in the State of São Paulo, Brazil, and funded by this State's Science Foundation (FAPESP).^[6]

Notes

References