First Report of Pierce's Disease of Grape Caused by Xylella fastidiosa in Oklahoma.

Bacterial leaf scorch caused by the bacterium Xylella fastidiosa was first identified in Oklahoma in American elm (Ulmus americanus L.) in the summer of 2004 (2). Subsequently, additional infections of other shade trees and ornamentals including oak (Quercus spp.), mulberry tree (Morus spp.), and sycamore (Platanus occidentalis) have been identified through sample submission to the Oklahoma State University, Plant Disease and Insect Diagnostic Laboratory. As of July 2008, no grape (Vitis spp.) samples positive for infection by X. fastidiosa were identified in Oklahoma. In August of 2008, leaves of four grape vines (Vitis labrusca 'Concord') grown in a home gardener's backyard located in Canadian County, OK were found to be exhibiting chlorosis and green fading colors with marginal browning. These symptoms included an undulating appearance with red-brown bands between the green and scorched areas. Vines exhibited 'matchstick' symptoms where the leaves dropped from the plant, but the petioles remained attached. All symptoms were consistent with those of Pierce's disease (3). Leaves from all four symptomatic vines and leaves from asymptomatic grapes (V. vinifera, unknown cultivar) from the Oklahoma Botanical Gardens located at Oklahoma State University, Stillwater were sampled. Genomic DNA was extracted from all samples with the DNeasy Plant Mini Kit (Qiagen, Germantown, MD). Samples were tested for the presence of X. fastidiosa by real-time PCR with Xylella genus-specific primers XfF1/XfR2 and dual-labeled TaqMan probe XfP2 (4). Infected tissue from a symptomatic oak tree was used as a positive control. Genomic DNA samples extracted from all four symptomatic grape vines and the symptomatic oak tree were PCR positive. Samples from the asymptomatic grape vine were PCR negative. Subsequent analysis was performed on the four symptomatic grape vine samples. X. fastidiosa-specific primers BBXFOUTF1 and BBXFOUTR1 were used to PCR amplify the gyrB gene (2). The amplification product was purified with the QuickClean 5M PCR Purification Kit (GenScript Corporation, Piscataway, NJ) and was subjected to automated sequencing (Oklahoma State University Recombinant DNA/Protein Resource Facility). BLASTN alignment (1) of the 340-bp sequences from the four symptomatic grape samples revealed 99 to 100% homology with the gyrB gene from a Pierce's disease strain of X. fastidiosa, 'Temecula' (GenBank No. AF534960). Remaining petiole tissues from the samples used above were subjected to serological tests for X. fastidiosa by ELISA (Agdia, Inc. Elkhart, IN). These tests confirmed the presence of X. fastidiosa in symptomatic grape tissue. To our knowledge, this is the first report of X. fastidiosa associated with grape and the first report of Pierce's disease in Oklahoma. This suggests that the geographic range for Pierce's disease should be extended to include central Oklahoma. References: (1) S. F. Altschul et al. J. Mol. Biol. 215:403, 1990. (2) B. R. Olson et al. Plant Dis. 90:108, 2006. (3) R. C. Pearson et al. Compendium of Grape Diseases. The American Phytopathological Society, St. Paul, MN, 1998. (4) N. W. Schaad et al. Phytopathology 92:721, 2002.