Presentation: Grapevine Red Blotch and Leafroll Viruses: Biology, Ecology, and Management

Marc Fuchs, Cornell University

The committee asked the speaker to address the following topics/questions during this webinar:

• What is the status of virus-vector interaction research for GRBD (and GLD if relevant), and what are the major questions that need to be addressed?
• Describe GRBV transmission biology by Spissistilus festinus.
• Provide your perspective on GRBV transmission ecology by S. festinus in different vineyard ecosystems.
• Are there regional differences or even site differences in the epidemiology of red blotch and leafroll in California?
• Provide an update on your research aimed at controlling vector-borne viruses impacting wine grapes. Provide your perspective on the potential and acceptance of biotechnological approaches for virus and vector control.
• Identify areas where significant progress could be made toward understanding vector biology/ecology and developing effective control strategies. What barriers need to be overcome?
• Discuss the role of the NCPN in grapevine certification program in New York and the challenges that the program has encountered.
• Share your perspective on grower adoption of management strategies and similarities and differences across virus-vector systems.

Q&A

Welcome and Introductions; Overview of Open Session

Anna Whitfield, Committee Chair

Epidemiology of Grapevine Virus Diseases and Plant Disease Management

Neil McRoberts, Professor of Plant Pathology, University of California, Davis; Director, Western Plant Diagnostic Network

• Describe the spatial and temporal spread of red blotch and leafroll in California; Are there regional patterns within California and beyond the borders of California?
• How do biotic and abiotic factors, such as climate variations and viral mixed infections, contribute to the epidemiology of grapevine leafroll and red blotch, and how can they be integrated into modeling efforts for a more comprehensive understanding?
• Considering the dynamic nature of plant diseases, especially in vineyards, what challenges and considerations are involved in modeling the long-term effects of grapevine leafroll and red blotch, and how reliable are current models in making predictions for future disease prevalence and spread?
• Provide your insight into growers’ perspective/understanding of red blotch and leafroll disease, including economic and social perspectives relevant to these diseases, willingness to adopt new technologies, and areawide management (barriers to adoption).
• Identify knowledge gaps in the biology and epidemiology of grapevine leafroll and red blotch that need to be addressed to provide understanding of the spread and control of these diseases.
• What are the key challenges with regard to extension? How is information translated, and what research areas have the greatest potential for payoff in disease and vector control?
• What are the barriers to the adoption of management tactics by growers?

Grapevine Red Blotch and Leafroll Disease Management

Monica Cooper, Director & ANR Advisor (Viticulture), UC Cooperative Extension, Napa County

Topics/questions to be addressed:

• Describe the significance of red blotch and leafroll diseases to wine grape and table grape production in California.
• Are there regional differences or even site differences in importance and severity of red blotch and leafroll in California?
• Describe challenges to areawide pest management programs and considerations to keep in mind for future efforts.
• What areas of red blotch and leafroll research and possible intervention points show promise for providing solutions for these vector-borne viruses? Describe challenges and

• considerations to keep in mind for future efforts (e.g., wine quality, social perception of technologies, grower concerns, etc.).
• What are the barriers to the adoption of management tactics by growers?
• Discuss any other aspects of red blotch and leafroll that you feel are important for the committee to take into consideration.

Grapevine Breeding for Disease/Vector Resistance

Peter Cousins, Grape Breeder, Winegrowing Research, E. & J. Gallo Winery

Topics/questions to be addressed:

• Significance of red blotch and leafroll diseases to wine grape production in California.
• Status of grapevine breeding for virus and vector resistance: best models and progress with red blotch and leafroll disease.
• What are the major technical barriers to progress in grape breeding for virus and/or vector resistance, and how could we overcome these barriers? How important is the inoculation method when screening for resistance to viruses?
• Describe challenges to grapevine breeding for virus resistance and considerations to keep in mind for future efforts (e.g., wine characteristics, social perception of technologies, grower concerns, etc.).
• Discuss any other aspects of red blotch and leafroll that you feel are important for the committee to take into consideration.

Welcome and Introductions; Overview of Open Session

Anna Whitfield, Committee Chair

Grapevine Red Blotch Virus and Vectors

Frank Zalom, Distinguished Professor of Entomology, Agricultural Experiment Station Entomologist and Extension Specialist, University of California, Davis

Mysore Sudarshana, Research Biologist, USDA-ARS Crops Pathology and Genetics Research, Davis, California

Topics/questions to be addressed:

• Status of virus-vector interaction research and what are the major questions that need to be addressed?
• Discuss GRBV transmission biology by Spissistilus festinus.
• Discuss GRBV transmission ecology by S. festinus in different vineyard ecosystems.
• Chemigation: What is the grapevine uptake efficiency? When is the optimal time for chemical application? What does the future of red blotch and leafroll vector chemical control look like?
• Progress toward identification of additional (or all possible?) red blotch vectors and key challenges.
• Identify areas where significant progress could be made toward understanding virus-vector biology and developing effective control strategies. What barriers need to be overcome?
• What are the most promising new technologies for vector control and challenges to be overcome for their application?
• Discuss any other aspects of red blotch and leafroll that you feel are important for the committee to take into consideration.

Impacts of GRBV on Grapes and Wine Composition

Anita Oberholster, Cooperative Extension Specialist in Enology, University of California, Davis

Topics/questions to be addressed:

• Provide an update on your research studying the effect of red blotch virus on grape and wine composition.
• Describe progress toward mitigating grapevine red blotch virus impact on final wine composition. How does the industry mitigate red blotch impact?
• Discuss the important biotic and abiotic factors that may further complicate the effect of red blotch on grapes and wine and cultivar responses to virus.
• Discuss any other aspects of red blotch and leafroll that you feel are important for the committee to take into consideration.

New Technologies for Virus Control

Protoplast-Mediated Gene Editing for Disease Resistance

David Tricoli, Manager, Plant Transformation Facility, University of California, Davis

Topics/questions to be addressed:

• Provide an update on your research studying the effect of red blotch virus on grape and wine composition.
• Describe progress toward identification of targets for gene editing for virus resistance.
• Describe progress toward efficient gene editing in grapevines.
• Identify areas where significant progress could be made toward developing effective control strategies. What knowledge gaps barriers need to be overcome?
• Provide your perspective on the potential and acceptance of biotechnological approaches for virus and vector control.
• Discuss any other aspects of red blotch and leafroll that you feel are important for the committee to take into consideration.

Grapevine Virus-Based RNA Interference (RNAi) Approaches to Target Grapevine Leafroll-Associated Viruses

Yen-Wen Kuo, Assistant Professor of Plant Pathology, University of California, Davis

Topics/questions to be addressed:

• Describe your progress toward new virus and/or vector control using grapevine virus-based RNA interference (RNAi) approaches to target grapevine leafroll-associated viruses.
• Provide an update on your research aimed at controlling vector-borne viruses impacting wine grapes.
• Discuss the progress and potential for vector insect-specific viruses to control vectors and/or viruses.
• Identify areas where significant progress could be made toward developing effective control strategies. What knowledge gaps and barriers need to be overcome?
• Provide your perspective on the potential and acceptance of biotechnological approaches for virus and vector control.
• Discuss any other aspects of red blotch and leafroll that you feel are important for the committee to take into consideration.

Grapevine Phytosanitary Regulations and the California Grapevine Registration and Certification Program

Maher Al Rwahnih, Director, University of California, Davis, Foundation Plant Services

Topics/questions to be addressed:

• Provide your perspective on the significance of red blotch and leafroll diseases to wine grape and table grape production and relative importance to the industry.
• Describe the status of grapevine phytosanitary regulations (in general), the status of the California certification program, challenges, and strategies that are working well and areas for improvement. Describe certification, protocols, and quarantine strategies implemented at the state level and policies and protocols for bringing in planting materials from outside of California.
• How is the planting material supply chain (from Foundation Plant Services to Nurseries to Growers) working?
• Describe the major barriers to progress in the implementation of phytosanitary measures to address virus issues in wine grapes; provide your opinion on strategies to overcome these barriers.
• How do international collaborations and agreements impact the implementation and enforcement of grapevine phytosanitary regulations?
• How do economic considerations and the financial impact of implementing phytosanitary measures influence the decision making of grape growers?
• Are there specific regions or grape varieties that are more vulnerable to the economic and qualitative impacts of red blotch and leafroll diseases?
• What are the major gaps in diagnostics for these viruses?
• What additional tool(s) and knowledge would be helpful for Foundation Plant Services with their efforts on clean plant production and to help growers implement phytosanitary standards?
• Are there specific knowledge gaps that, if addressed, could significantly improve the efficiency and accuracy of clean plant production programs?

Welcome and Introductions; Overview of Open Session

Anna Whitfield, Committee Chair

Q&A on Grapevine Leafroll Disease (GLD) and its Management in South Africa

Gerhard Pietersen, Senior Researcher, Patho Solutions; Committee

The committee asked the speaker to address the following topics/questions in their pre-recorded presentation, which was submitted beforehand for the committee to view (available at the study website):

• Can you provide an overview of the status of grapevine leafroll disease (GLD) in South Africa, including its prevalence and impact on vineyards?
• What are the primary methods used in South Africa for diagnosing GLD?
• What are the key strategies employed in South Africa for managing GLD, both in terms of prevention and control?
• Can you discuss any specific cultural practices or vineyard management techniques that have been effective in reducing the spread and impact of GLD?
• Are there any challenges or unique considerations in managing GLD in the South African context, such as climate, grapevine varieties, or regulatory issues?
• What are the best management practices for implementing rouging and replanting strategy in South Africa, including their approach to early identification of infected vines, rouging protocols, thresholds for replanting, and the economics of implementation?
• What is the industry-wide adoption rate of the rouging and replanting strategy?
• What are some of the barriers to adopting the rouging and replanting strategy?
• How do South African growers deal with the management of multiple generations grapevines as a consequence of the rouging and replanting strategy?

• Can you speak to the issue of the so-called bad neighbors with respect to GLD management and how this is dealt with in South Africa?

Q&A on Why Growers Adopt Best Management Practices

Mark Lubell, Professor, University of California, Davis; Committee

The committee asked the speaker to address the following topics/questions in their pre-recorded presentation, which was submitted beforehand for the committee to view (available at the study website):

• What are the barriers to grower adoption of disease/pest management practices? How can grower demographics (age, income, primary language, etc.) and communication strategies influence grower adoption?
• Can you share any case studies or examples of successful collaborations between the social science research community and growers in addressing disease and pest management challenges?
• In your experience, what communication methods or platforms have been most effective in disseminating information about disease and pest management practices to growers?
• How can we increase research utilization and ensure that the best available knowledge is used to inform grower practices?
• What are the key considerations for designing outreach and education programs aimed at improving grower adoption of disease and pest management practices? What are the best practices for fostering communal (area-wide) management of diseases and pests?
• How can we address potential socioeconomic disparities in access to resources and information related to disease and pest management in farms (vineyards)?

Q&A on Airborne and Spaceborne Imaging Spectroscopy for Early Grapevine Viral Disease Detection

Katie Gold, Assistant Professor of Grape Pathology, Cornell University; Committee

• What is the current state of research on hyperspectral imaging for detecting grapevine viruses such as leafroll and red blotch?
• What are the major roadblocks in applying hyperspectral imaging to virus detection?
• How early in the infection process can hyperspectral imaging detect viral infections in grapevines? Is it effective for detecting asymptomatic infections?
• What specific spectral signatures or patterns are indicative of grapevine viruses, and how reliable are they for accurate diagnosis?
• Are the challenges different for asymptomatic and symptomatic plants? Do you expect that co-infection also complicates this?
• What do you prefer as a ground-truthing method (i.e., ELISA/PCR?) and is ground-truthing data a challenge?
• Are there any ongoing research projects or future directions in this field that you find particularly promising or exciting?
• Are there are any specific camera instruments/vendors that you would recommend for hyperspectral imaging given that the performance continues to improve and cost to fall (Cubert Hyperspectral, for example)?