[8] While the largest outbreaks of X. fastidiosa–related diseases have occurred in the Americas and Europe, this pathogen has also been found in Taiwan, Israel, and a few other countries worldwide.

[12][13][14] A strain of X. fastidiosa responsible for citrus variegated chlorosis was the first bacterial plant pathogen to have its genome sequenced, in part because of its importance in agriculture.

[15] Due to the significant impacts of this pathogen on agricultural crops around the world, there is substantial investment in scientific research related to X. fastidiosa and the diseases it causes.

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.

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. sandyi is thought to have originated in the southern part of the United States, and is notable for causing oleander leaf scorch.

[24] 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.

On a macroscopic scale, plants infected with a X. fastidiosa-related disease exhibit symptoms of water, zinc, and iron deficiencies,[27] manifesting as leaf scorching and stunting in leaves turning them yellowish-brown, gummy substance around leaves,[27] fruit reduction in size and quality,[27] and overall plant height.

[citation needed] Severe PD symptoms include shriveled fruit, leaf scorching, and premature abscission of leaves, with bare petioles remaining on stems.

[30] Coffee Leaf Scorch (CLS) is a disease caused by the causal agent Xylella fastidiosa that is economically significant in Brazil.

[31] Citrus variegated chlorosis (CVC), another significant disease in this region caused by a strain of X. fastidiosa has been shown to infect coffee plants with CLS.

[31] X. fastidiosa was discovered in Apulia, Italy in 2013 for the first time as a destructive disease agent of olive trees and likely came from strains present in asymptomatic plant material imported from Costa Rica.

[33] X. fastidiosa occurs worldwide, though its diseases are most prominent in riparian habitats including the southeastern United States, California, and South America.

[37] The disease is endemic in Northern California, being spread by the blue-green sharpshooter, which attacks only grapevines adjacent to riparian habitats.

[40] In a unique effort, growers, administrators, policy makers, and researchers are working on a solution for this immense X. fastidiosa threat.

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,[42] developed and managed by the Public Intellectual Property Resource for Agriculture (PIPRA).

[35] The disease caused rapid decline in olive grove yields, and by April 2015, was affecting the whole Province of Lecce and other zones of Apulia,[7][48] though it had not previously been confirmed in Europe.

[49] The subspecies involved in Italy is X. f. pauca, which shows a marked preference for olive trees and warm conditions and is thought to be unlikely to spread to Northern Europe.

[49][51] The disease causes withering and desiccation of terminal shoots, distributed randomly at first but then expanding to the rest of the canopy[51] resulting in the collapse and death of trees.

[51] The most severely affected olives are the century-old trees of local cultivars Cellina di Nardò and Ogliarola salentina.