Adoption of Best Management Practices for Grapevine Leafroll and Red Blotch Diseases: A Survey of West Coast Growers

Grapevine leafroll disease (GLD) and red blotch disease (RBD) threaten the sustainability of the U.S. wine grape industry. To understand the factors influencing the adoption of disease management practices, we surveyed wine grape industry professionals in California, Oregon, and Washington (n = 154). Economic factors were the fundamental cost of implementing management practices and the ability to sell products from diseased vines (salability). Respondents who encountered reduced salability were more likely to adopt virus testing, replace infected vines, and view these practices as economically favorable. Salability was a strong driver for adoption among Californian respondents but less so in Washington, where wineries appeared more willing to accept infected products. Respondents who had acquired technical knowledge of disease ecology were more likely to adopt management practices and to perceive them as economical. Conversely, when there was a lack of knowledge of GLD ecology, notably that mealybugs transmit the pathogen, adoption was reduced, and practices were considered less economical. Factors affecting adoption were broadly generalizable across diseases. However, knowledge of GLD ecology was more strongly associated with adoption, likely reflecting the remaining knowledge gaps in RBD related to vector ecology and field spread. An emphasis on grower knowledge acquisition and the development of economical disease management practices can improve adoption of best management practices for viral diseases of grapevine. [Graphic: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license

Meeting the Challenge of Viral Disease Management in the US Wine Grape Industries of California and Washington: Demystifying Decision Making, Fostering Agricultural Networks, and Optimizing Educational Resources

Leafroll and red blotch are two of the most consequential viral diseases threatening the sustainability of the wine grape industry. To promote uptake of management practices, there is a critical need to understand the motivating factors for decision makers and optimize the dissemination and acquisition of knowledge. From 2019 to 2020, we conducted semi-structured interviews with 42 wine grape industry professionals (“decision makers”) in the Western United States, from California (n = 32) and Washington (n = 10). The interview questions explored the perceptions and experiences of these decision makers as they learned about disease ecology, interacted with their immediate and extended community, and adopted management practices. Utilizing qualitative thematic analysis, we identified nine economic, knowledge, and social-behavioural factors along with 24 sub-factors. These factors illustrated the interplay between knowledge, communication, economics, labour, government subsidies, regulatory practices, and collaborative efforts that influence adoption. The quality of knowledge dissemination emerged as a critical aspect. Using the interview data along with a quantitative survey (n = 145), we also explored how growers use 14 educational resources to learn about grapevine viruses. Using these findings, extension educators can optimize their activities to disseminate knowledge on grapevine viral disease management. In total, this study provides context for the agricultural industry, research scientists, extension educators, and other supporting partners of the financial, interpersonal, and technical issues that must be overcome to successfully manage grapevine viral diseases

Characterization of grapevine leafroll-associated virus 3 genetic variants and application towards RT-qPCR assay design

Grapevine leafroll-associated virus 3 (GLRaV-3) is the most widely prevalent and economically important of the complex of RNA viruses associated with grapevine leafroll disease (GLD). Phylogenetic studies have grouped GLRaV-3 isolates into nine different monophyletic groups and four supergroups, making GLRaV-3 a genetically highly diverse virus species. In addition, new divergent variants have been discovered recently around the world. Accurate identification of the virus is an essential component in the management and control of GLRaV-3; however, the diversity of GLRaV-3, coupled with the limited sequence information, have complicated the development of a reliable detection assay. In this study, GLRaV-3 sequence data available in GenBank and those generated at Foundation Plant Services, University of California-Davis, was used to develop a new RT-qPCR assay with the capacity to detect all known GLRaV-3 variants. The new assay, referred to as FPST, was challenged against samples that included plants infected with different GLRaV-3 variants and originating from 46 countries. The FPST assay detected all known GLRaV-3 variants, including the highly divergent variants, by amplifying a small highly conserved region in the 3' untranslated terminal region (UTR) of the virus genome. The reliability of the new RT-qPCR assay was confirmed by an enzyme linked immunosorbent assay (ELISA) that can detect all known GLRaV-3 variants characterized to date. Additionally, three new GLRaV-3 divergent variants, represented by four isolates, were identified using a hierarchical testing process involving the FPST assay, GLRaV-3 variant-specific assays and high-throughput sequencing analysis. These variants were distantly related to groups I, II, III, V, VI, VII and IX, but much similar to GLRaV-3 variants with no assigned group; thus, they may represent new clades. Finally, based on the phylogenetic analysis, a new GLRaV-3 subclade is proposed and named as group X