Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2004
Publication Date: 9/11/2004
Citation: Huang, Q., Brlansky, R.H., Barnes, L., Li, W.N., Hartung, J.S. 2004. First report of Oleander leaf scorch caused by Xylella fastidiosa in Texas. Plant Disease. 88:1049. Interpretive Summary: Xylella 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, oak and is reported on oleander in California and Florida. Recently, we observed leaf scorch symptoms in oleanders in various locations in Texas. In order to determine whether X. fastidiosa was the causal agent of the disease, we first utilized an antibody-based method and the result of the test was positive, indicating the presence of the bacterium in the affected oleanders. We then isolated a slow-growing bacterium from the affected plant sample, and the bacterium was shown to cause the leaf scorch disease in oleanders when mechanically inoculated to the plants. The bacterium was re-isolated from inoculated plants that became diseased. This is the first time that X. fastidiosa has been found to cause oleander leaf scorch disease in Texas. 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 on oleander in California and Florida. Recently, leaf scorch symptoms were observed in oleanders at various locations in Texas. The symptomatic varieties from Moody Gardens in Galveston, Texas reacted positively in ELISA, and colonies characteristic of X. fastidiosa were isolated from the symptomatic varieties. Fluorescing bacteria were also found in symptomatic varieties by membrane entrapment immunofluorescence (MEIF). ELISA and MEIF tests, as well as bacterial isolations from asymptomatic varieties were negative. Mechanical inoculation of oleanders with X. fastidiosa cultured from diseased oleanders caused oleander leaf scorch disease and the bacterium was re-isolated from inoculated plants that became diseased. Symptomatic samples from a residential area west of Galveston and from Harlingen, Texas were tested positive for X. fastidious by MEIF. Other ELISA-positive samples were obtained from symptomatic oleanders from Austin, San Antonio and El Campo, Texas. Our report is the first to show the causal role of X. fastidiosa in oleander leaf scorch in Texas, and the presence of the disease in different locations in Texas, thus extending the geographic range of this important bacterial disease.