Bacterial Leaf Scorch Caused by Xylella Fastidiosa: A Kentucky Survey; A Unique Pathogen; And Bur Oak, A New Host

Abstract

Bacterial leaf scorch caused by Xylella fastidiosa was detected using an ELISA test from 1989 to 1993 in symptomatic pin, red, shingle, and white oak; sycamore; and red maple in 16 Kentucky cities and towns distributed statewide. The disease was also detected in southern Indiana and in Tennessee. Leaf petiole xylem elements of affected trees were partially occluded with bacteria. Examination of the causal agent by electron microscopy revealed bacteria with unusual scalloped or rippled cell walls, typical of X. fastidiosa. Bacterial leaf scorch was identified for the first time in bur oak (Quercus macrocarpa ) in Lexington, Kentucky. Symptoms included marginal leaf necrosis, premature leaf browning, and defoliation. The disease was confirmed by detecting the pathogen with an ELISA test and by electron microscopic observation of the causal agent in leaf petiole tissues. Detection of bacterial leaf scorch has now progressed from coastal states to the U.S. interior.