Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2003
Publication Date: May 13, 2004
Citation: Huang, Q. First Report of Xylella Fastidiosa Associated with Leaf Scorch in Black Oak in Washington, DC. Journal of Plant Disease. v:88, pp:224. Interpretive Summary: We recently observed a disorder in black oak with symptoms similar to those seen in Xylella fastidiosa-infected leaves of red oak. X. fastidiosa is a slow growing, xylem inhabiting, nutritionally fastidious and insect-transmitted bacterium. It has a very wide host range, affecting over 30 plant families including both mono- and dicotyledonous plants. The bacterium is associated with bacterial leaf scorch and decline in many economically important landscape trees and shrubs including elm, sycamore, maple, oleander, and 17 species of oak including bur, pin, scarlet, shingle and white oaks. It also causes significant economic losses in many agriculturally important plants including grape (Pierce's Disease) and citrus (Citrus Variegated Chlorosis) in the United States and Brazil, respectively. In order to determine whether X. fastidiosa was present in the affected black oak, we utilized an antibody-based method and the result of the test was positive, indicating the presence of the bacterium in the affected black oak specimen. We also isolated a slow-growing bacterium from the affected plant sample, and the bacterium was confirmed to be X. fastidiosa using a DNA-based method. This is the first time that X. fastidiosa has been found associated with a black oak tree. Our work will be of value primarily to plant pathologists and entomologists interested in diseases caused by X. fastidiosa.
Technical Abstract: Bacterial leaf scorch caused by Xylella fastidiosa has been reported in 17 species of oak including bur, pin, red, scarlet, shingle and white oaks. Recently, a leaf scorch symptom characterized by marginal necrosis of leaves bordered by a darker brown band was observed in a mature black oak (Quercus velutina Lam.) at the U.S. National Arboretum in Washington, D.C. Leaf petiole extracts of the black oak reacted with an antiserum specific for X. fastidiosa in an enzyme-linked immunosorbent assay. A slow-growing bacterium was cultured from leaf petioles of the affected black oak tree on periwinkle wilt plates. When the cultured bacterium was subjected to polymerase chain reaction (PCR) with primers specific for X. fastidiosa, a 472-bp PCR product was detected. The PCR product was confirmed to be the predicted X. fastidiosa product by sequencing and sequence comparison with the reported genomic sequence of X. fastidiosa. Enzyme-linked immunosorbent assay and bacterial isolation from leaf petioles of a nearby symptomless white oak (Q. alba L.) tree were negative. This is the first report of X. fastidiosa associated with leaf scorch in black oak in the United States, thus expanding the host range of the bacterium in economically important landscape tree species.