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United States Department of Agriculture

Agricultural Research Service

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Research Project: An Invasive Pest and an Emerging Disease: A Dangerous Mix for West Coast Vineyards

Location: Horticultural Crops Research

2011 Annual Report

1a. Objectives (from AD-416)
1) Identify the distribution of GLRaV species throughout the season to determine if the observed increased incidence and damage results from changes in the GLRaV complex, combinations of GLRaV species, or new relationships between the pathogen(s) and its insect vectors. 2) To determine seasonal changes in the occurrence of both pathogen and vector in order to provide a better understanding of GLRaV epidemiology and leafroll incidence. 3) To investigate the impact of conventional and sustainable mealybug controls on the levels of disease incidence. 4) To develop an outreach program on GLRaVs and mealybugs.

1b. Approach (from AD-416)
Determine the etiological agent(s) of leafroll disease in vineyards where it is of critical economic importance and where it is considered of minor importance, allowing for comparison of symptoms and the development of reliable and sensitive diagnostic tools targeted to the pathogen. Furthermore, establishing rates of leafroll disease incidence and distribution of GLRaV types throughout the sampled regions will provide a baseline for future efforts in controlling the spread of these pathogens. Combined with the vineyard profile data collected, analysis of this data with tools such as ArcGIS and statistical correlations will also provide initial information on (a) the distribution and abundance of the insect vectors associated with GLRaV, and (b) relationships between mealybug species and different GLRaV types. Survey vineyard blocks in Napa and Sonoma Counties for the presence of both vector and pathogen. Use natural populations to investigate their association and link their seasonal population densities to leafroll incidence. Manipulate mealybugs on infested plants to determine acquisition efficiencies at different times of the season and when the vector is feeding on different plant parts. Compare conventional vs. sustainable controls for vine mealybug and record changes in leafroll incidence. Specialty Crops Research Initiative. Documents Reimbursablew ith UC Berkeley. Log 39181.

3. Progress Report
This research is designed to understand the relationship between mealybugs and transmission of grapevine leafroll virus 3 in vineyards in Oregon. Grapevine leafroll virus 3 (GLRaV-3) is transmitted by mealybugs that feed on grapevines. This is part of a larger Specialty Crops Research Grant that is studying this problem in the western United States and is being done in collaboration with colleagues at Washington State University, Oregon State University, U.C. Davis and U.C. Berkeley. The project involves entomologists and virologists from each of the three west coast states. In Oregon, the major grapevine leafroll viruses are GLRaV-3 and GLRaV-2. The entomologist on the project at Oregon State University is monitoring mealybug populations in these same vineyards. We are examining the titer (concentration) of these viruses in infected plants over several growing seasons and mapping the incidence of these viruses in six vineyards in Oregon over the duration of the project. In the Willamette Valley of Oregon, where mealybug populations are very low, we have not seen any year over year spread in the first two years of the project. However, in southern Oregon where mealybug populations are much higher, we have seen year over year spread of GLRaV-3. For situations where mealybug populations are high and GLRaV-3 is spreading, when is the best time to control mealybugs to reduce the transmission of the virus? If the virus titer is low early in the season, does this translate to inefficient transmission by the mealybug vector? If yes, can sprays to control mealybugs early in the season be reduced without having an impact on the transmission of GLRaV-3. We collected leaf tissue from young, mid-aged, and older leaves from five vines of Pinot noir self rooted and grafted plants infected with GLRaV-3, weekly during the growing season (June 1 through October 1) and tested these for virus before storing the extracted RNA at -80C. We have also developed a quantitative PCR test for GLRaV-3 and are in the process of evaluating the samples collected in 2010 for virus concentration through the growing season. For grapevine leafroll virus 2, there is no known vector. Other viruses related to GLRaV-2 are aphid transmitted. We have identified a vineyard with high levels of GLRaV-2 in multiple cultivars of grapevines. It is possible that all cultivars were planted with GLRaV-2 infections, but this may also provide a location where there is an active vector for GLRaV-2. Since this site is infested with Phylloxera we are investigating the possibility that Phylloxera can transmit GLRaV-2, since Phylloxera is essentially a root feeding aphid.

4. Accomplishments

Last Modified: 06/24/2017
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