Causal role of Xylella fastidiosa in oleander leaf scorch disease

A lethal leaf scorch disease of oleander (Nerium oleander) appeared in sout hern California in 1993. A bacterium, Xylella fastidiosa, was detected by c ulturing, enzyme-linked immunoassay, and polymerase chain reaction in most symptomatic plants but not in symptomless plants or negative controls. Inoc ulating oleanders mechanically with X. fastidiosa cultures from diseased ol eanders caused oleander leaf scorch (OLS) disease. The bacterium was reisol ated from inoculated plants that became diseased. Three species of xylem sa p-feeding leafhoppers transmitted the bacterium from oleander to oleander. The bacterium multiplied, moved system-ically, and caused wilting in Madaga scar periwinkte (Catharanthus rosea) and leaf scorch in periwinkle (Vinca m ajor) in a greenhouse after inoculation with needle puncture. No bacterium was reisolated from grapevine (Vitis vinifera), peach (Prunus persica), oli ve (Olea europaea), California blackberry (Rubus ursinus), or valley oak (Q uercus lobata) mechanically inoculated with OLS strains of X. fastidiosa. A 500-bp sequence of the 16S-23S ribosomal intergenic region of oleander str ains showed 99.2% identity with Pierce's disease strains, 98.4% identity wi th oak leaf scorch strains, and 98.6% identity with phony peach, plum leaf scald, and almond leaf scorch strains.