Hot-Water Treatment of Pecan Scions as a Means of Phytosanitation to Reduce the Potential Introduction of Xylella fastidiosa, the Causal Agent of Pecan Bacterial Leaf Scorch, into Orchards and New Geographic Regions
Pecan (Carya illinoinensis) bacterial leaf scorch is a chronic disease of pecan that reduces yield, causes defoliation, and retards growth. The causal agent of this disease, Xylella fastidiosa subsp. multiplex, is a xylem-inhabiting bacterium that can be transmitted in pecan by grafting with infected plant tissue or by insects in the families Cercopidae and Cicadellidae that feed exclusively in the xylem. No economically effective treatment for this disease exists once a tree becomes infected, and no immune pecan cultivars have been identified. Infection is persistent and disease and yield loss will occur annually. A simple, hot-water treatment in which pecan scions are submerged in water at 46 degrees C for 30 min prior to grafting provides a means for reducing the potential introduction of X. fastidiosa into orchards through grafting without harming the viability of the scions. The recent increase in international germplasm exchange within the genus Carya, as a result of interest in pecan production outside of its native range (North America), increases the probability of pathogen and insect introductions into new geographic regions. Such introductions may result in significant changes in the health of the Carya species, as well as other non-native and native plant hosts, in these regions. Xylella fastidiosa is known to infect over 100 plant species and to cause disease in economically important crops, ornamentals, and landscape trees. The geographic distribution of X. fastidiosa, with the exception of Chinese Taipei, is currently limited to the Americas. Application of the hot-water treatment to pecan scions may not only slow the spread of X. fastidiosa in areas where it already exists, but also reduces the introduction of this pathogen into regions where it is not established. This treatment should be adopted as a standard phytosanitation treatment in regions that import pecan scion wood.