Not all Xylellas are born equal V

coffee berries being harvested

The last blog of this series on Xylella focuses on other plants susceptible to Xylella fastidiosa, i.e. on pecan trees and on coffea species. A small update on olive trees concludes the blog.

Graph showing spread of xylella in key crops
Fruit trees susceptible to Xylella fastidiosa | BIOVEXO compilation


Pecan bacterial leaf scorch (PBLS), caused by Xylella fastidiosa subsp. multiplex, can cause severe disease in some pecan cultivars, resulting in substantial yield loss. Symptoms of PBSL include tan to light brown necrotic lesions on leaflet tips that progress in a uniform pattern toward the leaflet’s base and will eventually result in premature defoliation. Xylella fastidiosa causes chronic infections from year-to-year and can live dormant, or in low concentrations, in the host without causing symptoms. Symptoms of pecan bacterial leaf scorch can present either on individual branches or systemically across the entire canopy of the tree.

PBLS has been confirmed to occur in the southern United States, including the states of Louisiana, Georgia, Texas, New Mexico, Arizona, and California. Scientific studies on PBLS have shown the pecan cultivar, ‘Cape Fear,’ to be highly susceptible to infection. No significantly resistant cultivars have been identified.

There is presently no cure for PBLS. Care should be taken not to inoculate other trees during grafting. It has been suggested recently that pecan scions should be completely submerged in water heated to 46°C for 30 minutes. This treatment is claimed to be over 90 percent effective.


Coffee leaf scorch (CLS), due to X. fastidiosa, was first identified in 1995 in Brazil and later in Latin American coffee-producing countries such as Costa Rica. Symptoms of CLS include drying of infected branches, shortening of internode regions, decreased fruit size, chlorosis, and early senescence of leaves. Plants also show irregular growth with an atypical curling appearance that gave rise to the Spanish name “crespera.” CLS affects plant productivity but rarely leads to plant death. The insect vector is the sharpshooter.

In 2012, four coffee plants with leaf scorch symptoms growing in a confined greenhouse were detected in France. One, a Coffea canephora (Robusta coffee) plant imported from Mexico, was identified as having Xylella fastidiosa subsp. fastidiosa/subsp. sandyi. The others, Coffea arabica plants imported from Ecuador, were allocated to X. fastidiosa subsp. pauca.

Xylella fastidiosa was presumptively diagnosed during a survey performed on ornamental Coffea arabica plants imported from Costa Rica and Honduras into the Netherlands in the autumn of 2014. These plants showed either mild leaf scorch symptoms, a range of “crespera”-like symptoms, or were asymptomatic.


Apart from the looming crises in the Mediterranean area, the presence of Xylella fastidiosa has been reported in olive trees showing leaf scorch symptoms in Argentina and Brazil. The two South American strains resulted differently from each other and from the Italian strain but were both classified as belonging to the subsp. pauca.

Olive leaves showing signs of xylella
Signs of xylella in an olive tree - dried, curled leaves and withered fruit

Xylella fastidiosa subsp. multiplex was also detected in olive trees grown in California. Strains of Xylella fastidiosa subsp. multiplex isolated from California olive trees are not known to cause disease on olive, although some can induce leaf-scorch symptoms on almond.

Final word

We hope you have enjoyed this series on some of the key species that can be affected by Xylella. Please follow the BIOVEXO Project on social media and help us spread the word about this threat!





And, of course, keep following our blog!


Leave a Reply

Your email address will not be published. Required fields are marked *