Host Specificity of Pecan Strains of Xylella fastidiosa subsp. multiplex.

Pecan (Carya illinoinensis) bacterial leaf scorch disease, caused by Xylella fastidiosa subsp. multiplex, causes defoliation and reduces terminal growth and nut yield. The pathogen is transmitted to pecan by xylem-feeding spittlebugs and leafhoppers and through graft transmission in the clonal propagation of cultivars. Xylella fastidiosa subsp. multiplex has a broad host range, infecting numerous hardwood tree species and some herbaceous species. There is evidence of additional host specialization within subsp. multiplex. Data presented here support the existence of host specialization with X. fastidiosa that infect pecan. In this study, mechanical inoculation was used to inoculate several plant species that are naturally infected by subsp. multiplex, including sycamore, red maple, purple-leafed plum, and blueberry with strains of X. fastidiosa from pecan. Hosts of three other subspecies were also inoculated with the pecan strains: grapevine (subsp. fastidiosa); oleander (subsp. sandyi); and mulberry (subsp. morus). Pecan was also inoculated with a strain of the pathogen from sycamore (subsp. multiplex) and a strain from grapevine (subsp. fastidiosa). In greenhouse tests, inoculum prepared from X. fastidiosa obtained from naturally infected pecan almost exclusively infected pecan. In addition, the subsp. multiplex strain from sycamore generally did not infect pecan, and the subsp. fastidiosa strain from grapevine did not infect pecan. The inability of the pecan strain to readily infect other hosts commonly located in the vicinity of pecan orchards affects the management recommendations for the disease in commercial pecan production by allowing management practices to focus on pecan orchards and insect vectors.