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Disease Note.

First Report of Bacterial Leaf Scorch Caused by Xylella fastidiosa on Sugar Maple and Sweetgum. J. R. Hartman, Department of Plant Pathology; University of Kentucky, Lexington 40546. U. E. Jarlfors, Department of Plant Pathology, and W. M. Fountain, Department of Horticulture and Landscape Architecture, University of Kentucky, Lexington 40546; and R. Thomas, Oldham County Cooperative Extension, LaGrange, KY 40031. Plant Dis. 80:1302. Accepted for publication 29 August 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1302B.

Bacterial leaf scorch, caused by Xylella fastidiosa, has been reported on landscape trees in coastal U.S. states from New York to Texas, and recently in bur, pin, red, and shingle oaks, and sycamore in Kentucky (I). In October 1995, the disease was identified in a mature sugar maple (Acer saccharum Marsh.) in Oldham County, KY, and in a 10-year-old sweetgum (Liquidambar styraciflua L.) in Lexington, KY. Symptoms included premature leaf browning and defoliation, and marginal necrosis of leaves. The diseased sweetgum was found near infected pin oaks, but other sweetgus nearby were unaffected. The diseased maple was growing in relative isolation from other tree species with leaf scorch and only healthy maples were nearby. The disease was confirmed by detecting the pathogen with an enzyme-linked immunosorbent assay specific for Xylella (Agdia, Inc., Elkhart, IN). Three samples of leaves with symptoms collected from diseased trees were positive while multiple samples from symptomless leaves and from symptomless trees were negative. Electron microscopy of leaf petiole tissues revealed xylem elements partially occluded with bacteria. The bacteria had characteristic scalloped or undulating cell walls. Bacterial leaf scorch is associated with death of many oaks in some Kentucky cities. This finding expands the host range for this increasingly important bacterial disease.

Reference: (1)J. R Hartman et al. J. Arboric. 21:77, 1995.