Survey of Xylella fastidiosa Infection in Prunus Germplasm in Gainesville, FL, USA

Abstract

The pathogen Xylella fastidiosa is a xylem-restricted, gram-negative bacterium that is known to cause diseases of many cultivated plant species. Recent outbreaks of X. fastidiosa diseases in Europe have brought attention to the impact of this pathogen, especially to perennial crops. Among the Prunus genus, X. fastidiosa is known to have a wide range of hosts, including plum, almond, peach, cherry, and apricot. Infected trees have reduced fruit quality, possibly resulting in unmarketable fruits, as well as reduced lifespan. There are no curative management options for X. fastidiosa diseases in Prunus; therefore, development of resistant or tolerant cultivars through breeding represents an efficient option to reduce the impact of this pathogen. In this context, the main objective of this study was to determine the occurrence of X. fastidiosa in germplasm of the Stone Fruit Breeding Program at the University of Florida located in Gainesville, FL, USA, under natural infection conditions. A total of 43 individuals representing 10 different genotypic groups within the Prunus genus were tested for the presence of X. fastidiosa. Additionally, we report a novel and easy sampling method using sawdust collected from tree trunks for the detection of this pathogen in Prunus and the development of an endogenous control for improving the diagnosis of this pathogen using real-time polymerase chain reactions. Our results showed a high incidence of X. fastidiosa in the germplasm tested, with more than 65% of the samples positive for the presence of the bacterial pathogen. However, X. fastidiosa was not detected in most of the P. mume samples tested, whereas almost all the P. mume × P. armeniaca hybrids were positive. Negative individuals were also identified in P. avium, P. campanulata, P. umbellata, and P. salicina × P. ceracifera. These trees have been planted in the field, exposed to natural infection for 4 to 11 years, and are considered to show field resistance. Finally, primers and probes based on the Prunus COX gene developed in this study can be used as an internal amplification control to enhance the interpretation of results of X. fastidiosa detection assays using sawdust samples.