User:Seanflaherty2003/sandbox

Xylella fastidiosa is rod-shaped, and at least one subspecies has two types of pili on only one pole; longer, type IV pili are used for locomotion, while shorter, type I pili assist in biofilm formation inside their hosts. As demonstrated using a PD-related strain, the bacterium has a characteristic twitching motion that enables groups of bacteria to travel upstream against heavy flow, such as that found in xylem vessels. It is obligately insect-vector transmitted from xylem-feeding insects directly into xylem, but infected plant material for vegetative propagation (e.g. grafting) can produce mature plants that also have an X. fastidiosa disease. In the wild, infections tend to occur during warmer seasons, when insect vector populations peak. The bacterium is not seed transmitted, but instead is transmitted through "xylem feed-ing, suctorial homopteran insects such as sharpshooter leafhoppers and spittle bugs" and has been historically difficult to culture (fastidious), as its specific epithet, fastidiosa, reflects.

X. fastidiosa can be divided into four subspecies that affect different plants and have separate origins. X. fastidiosa subsp. fastidiosa is the most studied subspecies, as it is the causal agent of PD; it is thought to have originated in southern Central America, and also affects other species of plants. X. f. multiplex affects many trees, including stone-fruit ones such as peaches and plums, and is thought to originate in temperate and southern North America. X. f. pauca is believed to have originated in South America. It is the causal agent of citrus variegated chlorosis (CVC) in Brazil and also affects South American coffee crops, causing coffee leaf scorch. X. f. sandyi is thought to have originated in the southern part of the United States, and is notable for causing oleander leaf scorch.

X. fastidiosa has a two-part lifecycle, which occurs inside an insect vector and inside a susceptible plant. While the bacterium has been found across the globe, only once the bacterium reaches systemic levels do symptoms present themselves. Once established in a new region, X. fastidosa spread is dependent on the obligate transmission by xylem-sap feeding insect. Within susceptible plant hosts, X. fastidiosa forms a biofilm-like layer within xylem cells and tracheary elements that can completely block the water transport in affected vessels.

Symptoms
Significant variation in symptoms is seen between diseases, though some symptoms are expressed across species. On a macroscopic scale, plants infected with a X. fastidiosa-related disease exhibit symptoms of water, zinc, and iron deficiencies, manifesting as leaf scorching and stunting in leaves turning them yellowish-brown, gummy substance around leaves, fruit reduction in size and quality , and overall plant height. As the bacterium progressively colonizes xylem tissues, affected plants often block off their xylem tissue, which can limit the spread of this pathogen; blocking can occur in the form of polysaccharide-rich gels, tyloses, or both. These plant defenses do not seem to hinder the movement of X. fastidiosa. Occlusion of vascular tissue, while a normal plant response to infection, makes symptoms significantly worse; as the bacterium itself also reduces vascular function, a 90% reduction of vascular hydraulic function was seen in susceptible Vitis vinifera. This bacterium rarely completely blocks vascular tissue. There usually is a slight amount of vascular function that keeps the plant alive, but makes its fruit or branches die, making the specific plant economically nonproductive. This can cause a massive drop on supply of quality fruit. Smaller colonies usually occur throughout a high proportion of xylem vessels of a symptomatic plant.

X. fastidiosa is a Gram-negative, xylem-limited illness that is spread by insects. It can damage a variety of broadleaved tree species that are commonly grown in the United States. X. Fastidiosa can be found in about 600 different plant species.


 * Withering and desiccation of branches
 * Leaf chlorosis
 * Dwarfing or lack of growth of the plant
 * Drooping appearance and shorter internodes
 * Shriveled fruits on infected plants
 * Premature fruit abscission
 * gum-like substance on leaves
 * hardening and size reduction of fruit

Collaborative efforts for resolutions
In a unique effort, growers, administrators, policy makers, and researchers are working on a solution for this immense X. fastidiosa threat. No cure has been found, but the understanding of X. fastidiosa and glassy-winged sharpshooter biology has markedly increased 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; 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, developed and managed by the Public Intellectual Property Resource for Agriculture (PIPRA).

Few resistant Vitis vinifera varieties are known, and Chardonnay and Pinot noir are especially susceptible, but muscadine grapes (V. rotundifolia) have a natural resistance. Pierce's disease is found in the Southeastern United States and Mexico. Also, it was reported by Luis G. Jiménez-Arias in Costa Rica, and Venezuela, and possibly in other parts of Central and South America. In 2010, X. fastidosa became apparent in Europe, posing a serious, real threat. There are isolated hot spots of the disease near creeks in Napa and Sonoma in Northern California. Work is underway at UC Davis to breed PD resistance from V. rotundifolia into V. vinifera. The first generation was 50% high-quality V. vinifera genes, the next 75%, the third 87% and the fourth 94%. In the spring of 2007, seedlings that are 94% V. vinifera were planted.

A resistant variety, 'Victoria Red', was released for use especially in Coastal Texas.