First Detection of Grapevine leafroll associated virus-7 in California Vineyards.

Grapevine leafroll is one of the most important viral diseases in grapevine and occurs wherever grapevines are grown. At least nine different Grapevine leafroll associated viruses (GLRaVs) belonging to different genera within the Closteroviridae family have been reported. Typical leafroll symptoms include downward rolling and interveinal reddening or yellowing of leaves, reduced fruit size, sugar content, and yield. Our laboratory has detected the presence of GLRaV-7 in many grapevine cuttings collected in California vineyards. During the 2005-2006 fall/winter testing season, symptomatic and asymptomatic grapevine varieties collected from different vineyards in California were tested for the detection of economically important viruses and processed for reverse transcription (RT)-PCR and ELISA. The RT-PCR assays using primers specifically designed for the detection of GLRaV-7 (C. Turturo et al., 13th ICVG [Abstr.], 2000) amplified a single band of approximately 200 bp in samples from selections of Chardonnay, Merlot, Pinot Noir, and Sauvignon Blanc cultivars. The same samples showed low or no reactivity to GLRaV-7 specific antibodies (BIOREBA AG, Reinach, Switzerland). The variability of detection by ELISA can be due to the lower sensitivity of ELISA as compared with RT-PCR and the uneven distribution of GLRaVs in grapevines (1). To confirm that the amplified DNA was GLRaV-7 specific, different isolates were sequenced and compared with the nucleotide and derived amino acid sequences obtained by Turturo et al. (13th ICVG [Abstr.], 2000). The California isolates showed 81 to 98% similarity with the Italian isolates. To our knowledge, this is the first report of GLRaV-7 in California and the United States. Our initial testing data indicates that GLRaV-7 is wide spread in California vineyards. Further studies will allow us to determine the potential effect of this virus in grapevines grown in California. Reference: (1) J. Monis, and R. K. Bestwick. Am. J. Enol. Vitic. 47:199, 1996.