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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

2012 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.

3. Progress Report:
This project aims to determine the risk of Grapevine leafroll associated virus -3 (GLRaV-3) to the grape industry in Oregon and to characterize other viruses that are present in Oregon vineyards. GLRaV-3 is transmitted by mealybugs and scale insects and is a threat to the wine industry in the Pacific Northwest. The virus is easier to detect late in the growing season, which suggests that virus titer increases over the season and possibly transmission efficiency by the vectors also increases during the season. In quantitative reverse transcription-PCR tests, it was determined that the virus titer of GLRaV-3 builds very quickly in the field and reaches its peak titer during the first generation of mealybug crawlers. This suggests that early season vector control is as important as late season control to minimize the spread of the virus. The impact of GLRaV-3 on fruit ripening was evaluated in self-rooted and grafted Pinot noir clones. In grafted clones, GLRaV-3 infection resulted in a significant decrease in sugar content of the fruit at harvest and also resulted in more uneven ripening of the fruit at harvest in terms of fruit color and firmness. We detected Grapevine fleck virus and Grapevine virus E in commercial vineyards in Oregon. The impact and distribution of these viruses in Oregon vineyards is being examined. The partial sequence of these two viruses has allowed us to develop primers that detect a broader range of viruses and will improve detection of these viruses for surveys, certification and quarantine purposes. This research was conducted in support of objective 3B of the parent project.

4. Accomplishments

Last Modified: 10/17/2017
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