Floral and Nursery Plants Research Unit, U.S. National Arboretum, USDA, ARS, Beltsville, MD 20705
University of Florida, Citrus Research Center, Lake Alfred 33850
Texas A&M University, College Station 77845
Fruit Laboratory, USDA, ARS, Beltsville, MD 20705
Bacterial leaf scorch caused by Xylella fastidiosa has been reported on oleander in California (3) and Florida (4). In June 2002, leaf scorch symptoms including chlorotic mottling of leaves, necrosis on leaf tips or whole leaves, defoliation, and shortened internodes were observed in oleander plants at various locations in Texas, including Galveston, Harlingen, Austin, San Antonio, and El Campo. The symptomatic varieties Calypso, Commandant Barthelemy, Lane Taylor Sealy, Little Red, Mrs. George Roeding, Mrs. Runge, Scarlet Beauty, and Petite Salmon, as well as symptomless varieties, Turner's Shari D and Sugarland from Moody Gardens in Galveston, Texas were sampled. All samples were tested for the presence of X. fastidiosa using enzyme-linked immunosorbent assay (ELISA) and bacterial isolation according to the methods of Huang and Sherald (2). All symptomatic varieties reacted positively in ELISA, and colonies characteristic of X. fastidiosa were isolated from all eight symptomatic varieties 10 to 15 days after incubation at 28°C. The colonies were confirmed to be X. fastidiosa using polymerase chain reaction (PCR) (2). ELISA tests and bacterial isolations from the symptomless Shari D and Sugarland varieties were negative. Membrane entrapment immunofluorescence (MEIF) (1) using the antibody CREC 26 to X. fastidiosa was also done on three of the symptomatic varieties and one asymptomatic variety obtained from Moody Gardens, and fluorescing bacteria were found only in the three symptomatic varieties. Symptomatic samples of Petite Salmon, one pink variety and one red variety obtained from a residential area west of Galveston, and a red oleander in Harlingen, TX, also tested positive with MEIF. Other ELISA-positive samples were obtained from symptomatic oleanders from Austin, San Antonio, and El Campo, TX. The X. fastidiosa bacteria isolated from the variety Lane Taylor Sealy were used to inoculate three red oleander plants by making an 8-cm-long vertical cut into the stem and then in 15 locations injecting approximately 15 μl of a X. fastidiosa suspension (108--9 cells per ml). The cut area was wrapped with Parafilm after inoculation, and the plants were kept at 29°C in a greenhouse. Three healthy red oleanders were inoculated with periwinkle wilt liquid medium for controls. Approximately 3 months after inoculation, chlorotic mottling along the edges of leaves was observed in the oleanders inoculated with X. fastidiosa, and the bacterium was reisolated from symptomatic leaves as described above. No symptoms were observed on the control plants, and bacterial isolation from the control plants was also negative. To our knowledge, this is the first report to show the causal role of X. fastidiosa in oleander leaf scorch and the presence of the disease in different locations in Texas, extending the geographic range of this important bacterial disease.
References: (1) R. H. Brlansky et al. Plant Dis. 74:863, 1990. (2) Q. Huang and J. L. Sherald. Curr. Microbiol. 48:73, 2004. (3) A. H. Purcell et al. Phytopathology 89:53, 1999. (4) R. L. Wichman and D. L. Hopkins. Plant Dis. 84:198, 2000.