Xylella fastidiosa can cause pecan leaf scorch
Several forms of leaf scorch diseases have been observed on pecan (Carya illinoinensis) and attributed to various causes, such as nutrition deficiencies, environmental problems or fungal pathogens. So far, various fungi (Phomopsis, Pestalotia, Epicoccum, Curvularia, Fusarium) had been thought to be associated with a particular form of leaf scorch disease which was accordingly called fungal leaf scorch disease. Symptoms were characterized by necrotic areas which first appeared on the tips or margins of leaflets and progressed towards the midribs. The advancing necrosis was often delimited by a black margin and affected leaflets abscised. In 1998, Xylella fastidiosa (EPPO A1 quarantine pest) was found in association with this disease. By completing Koch’s postulates, Sanderlin and Heyderich-Alger (2000) have now shown that X. fastidiosa can cause leaf scorch in pecan orchards in Louisiana. It appears that X. fastidiosa is the primary pathogen, as the disease can develop in the absence of fungi. It is likely that fungi are secondary pathogens, or saprophytes developing on dead tissues. It was proposed to call the disease pecan bacterial leaf scorch. It is noted that, unlike other diseases caused by X. fastidiosa on other host plants, pecan bacterial leaf scorch does not lead to the death of pecan plants.
Sources
Sanderlin, R.S.; Heyderich-Alger (2000) Evidence that Xylella fastidiosa can cause leaf scorch disease of pecan.
Plant Disease, 84(12), 1282-1286.