Grapevine Leafroll Disease, a General Detail Study and Evaluation

Grapevine leafroll disease causes poor color development in red grape varieties and non-uniform maturation of fruit in Vitis vinifera. It also has been reported to cause delay in fruit maturation from 3 weeks to a month and crop losses of as much as 20-40%. To date 9 different viruses, named Grapevine leafroll associated virus (GLRaV) types 1 to 7, 9, and a newly discovered virus from a Carnelian clone which tentatively has been named GLRaV-Carnelian are proven to be associated with leafroll disease. This project was planned to study the effects of these GLRaV types 1 to 5, -7 and -9 and their combination of two on Cabernet Franc grafted on 9 different rootstocks including AXR #1, Mgt 101-14, 110R, 3309C, 5BB, 420A, Freedom, St. George 15 and St. George 18. In this experiment 20 replicates for each treatment will be used. Total of 6578 Cabernet Franc plants on 9 different rootstocks were produced by bench grafting. In 2009-2010, 3841 vines were inoculated with individual viruses or the combination of two per. Remaining 1186 plants will be inoculated in 2011. Seven acres of land in the Department of Plant Pathology Field Station at UC Davis has been prepared for planting by installing the drip irrigation pump and drip irrigation lines, leveling and setting up the trellis and planting 3841 virus-inoculated and healthy control plants. In 2010-2011, we continue the time course study choosing two months interval for testing the plants for virus titer. The viruses used in this experiment included GLRaV types 1-5 and GLRaV-2RG. The samples were tested by reverse transcriptase polymerase chain reaction (RT-PCR) and real time RT-PCR using TaqMan probe (qPCR) and the results were compared. The data showed that both methods were able to detect the viruses in the samples regardless of the time of collection. In general, the titer of the viruses selected in this investigation was higher in February and lowest in early growing season in the month of April.