QBE Lab Department of Plant Pathology UC Davis

QBE Lab UC Davis Department of Plant Pathology

Author: Kari Arnold

Upcoming Conferences

Conferences and annual meetings are great ways to network with other scientists, researchers, and growers. These venues allow for a meeting place where we can display and discuss our work, and also a great way to learn about current work in our research fields. A few of the QBE lab members are planning to present their work at a number of conferences this summer, namely the American Phytopathological Society (APS) annual meeting in Pasadena, CA, and the American Society for Enology and Viticulture (ASEV) annual meeting in Portland, OR. Robin Chourdhury, a Melhus award winner, will present his work on the “Epidemiology and Control of Spinach Downy Mildew in Coastal California” at the 2015 APS meeting. The research is a collaboration with Steven T. Koike, Alan Fox, Krishna Subbarao, and Steven J. Klosterman. Christophe Gigot will present his work on “Spatial pattern analysis of the incidence of strawberry angular leaf spot under outdoor growing conditions in California”at the 2015 APS. Christoph’s research involves a collaboration with William Turechek. Kari Arnold will present work on “Assessing the benefits of disease management by interpreting an ecological survey of grapevine viruses when contrasted with “planting booms” at 2015 APS and at ASEV 2015 she will discuss “Interpreting a multi-virus survey and designing and delivering virus sampling protocols for industry-wide benefits”, of these involve collaboration with Monica Cooper and Deborah Golino.

So Far, So Good, So What? An Update on Leafroll

Ok, I may have intended to quote something in the title, but I will let you figure that out….unless you already know, and if so, I will offer you a digital high five.  Either way, the current status of the leafroll project and I parallels the saying “So far, so good, so what?” quite eloquently, and here’s why…

As a part of my transition into PhD-hood, I have had to review my leafroll (GLRaV-3) story many times over in presentation form and award application/proposal form, in order to tell others what has happened so far, ensure them that it is in fact “good”, and what importance in the big picture does it represent (the “so what?” part), so the retrospect aspect on my shuttle bus ride into Davis is coming in quite handy.  Yet every time I tell the story, I am still stunned to think that we made it this far.  It takes an interesting batch of people to assess the appropriate amount of information, and relay that information back to those who need it, then back away and wait to see if the up take will lead to change within the system.  It is a careful balance, we have worked diligently, watched wondering, waiting to see if it will work…..so far, so good….so what?  Here’s my story, thus far:

Background and Rationale:
Grapevine leafroll associated virus -3 (GLRaV-3) is a grapevine virus that reduces vigor and yield in vines, and qualitative parameters in wine (Mannini et. al. 1996, Mannini et. al. 2006). A certification program is in place in response to the need for virus tested clean stock (Alley and Golino, 2000, Olmo, 1951); however the use of noncertified stock is still common in California vineyards (Golino, et. al. 2008). Four species of mealybugs commonly found in California vineyards are known to transmit GLRaV-3 and GLRaV-3 is currently spreading in Napa Valley (Golino, et. al. 2008).
Current Work:
Knowledge of the active dispersal of GLRaV-3, mixed with the regional arrangement of multiple landowners and corporate agencies farming vineyards under multiple variations of cultivation, means the control of GLRaV-3 was and still is highly dependent upon area wide management groups. Yet barriers to adoption of new practices by farmers come in many forms, including lack of familiarity, uncertainty about the potential value, or mistrust about the extent to which others will participate in collective actions (Gent, et. al. 2013, Lubell, et. al. 2012). Two studies began simultaneously, in order to promote regional neighbor related action in terms of GLRaV-3 control. The first study, a Q-method (Stephenson, 1954a) approach, was used to assess collective concerns involving GLRaV-3 management. The second study was an epidemiological characterization of GLRaV-3 with the use of multiple diagnostically verified disease maps from Napa and other parts of the world, in order to better understand parameters of disease dispersal for GLRaV-3 management. As a result of presenting preliminary data to growers, area wide management groups have formed, and new ones are forming in order to control GRaV-3 on a regional level.
The first study used Q-method in order to assess the opinions of the growers’ subjectivities on the subject of GLRaV-3 management. Three workshops were held in the Napa Valley at which invited participants were asked to write down their views in response to a set of open-ended questions about leafroll, its’ impacts and the prospects for cooperative management of the disease. Responses were sorted into thematic groups (e.g. statements about financial issues, clean plant material, interpersonal trust, etc.). A small subset of response statements which encapsulated the groups of opinions was extracted. This resulted in a set of 47 statements. Invitations were issued via email and by personal contacts to a further group of participants drawn from the Napa Valley grower and winemaker communities generating a participant group of 37 individuals, then later an additional 12 participants from central CA. These people were interviewed on a one-to-one basis and the participants ranked the statements by the degree to which each one accorded with their own views. The resulting two-way table of data, in which each row gives the numerical rank assigned to each statement by one participant, was then subjected to a principal components analysis to extract information regarding the distribution of opinions over the group of participants and to identify meaningful classifications of the responses. The analysis revealed a wide diversity of opinion distributed among some broad categories of response. This information was then quickly redistributed to growers in the form of multiple presentations at grower conferences in order to assist in team building among potential grower groups. A journal article is currently in preparation from this work.

The second study utilized field maps from previous literature as well as from diagnostically RT-PCR verified industry disease maps showing the disease status of individual vines. These census maps were analyzed by exhaustive quadrat-based mapping in order to better understand the epidemiology of GLRaV-3; particularly to support sampling strategy and disease detection. The nature of the vector and the nature of the virus acquisition and transmission lead the pattern of disease in the field to be aggregated. The early juvenile stages of mealybugs are considered the most efficient at acquisition and transmission, (Golino et. al. 2008) and these juveniles are unable to fly. Therefore, apart from being passively dispersed in wind gusts, they typically crawl along vine rows. The data for disease incidence at individual vine, quadrat and block scales were analyzed using a number of different statistical approaches appropriate for disease incidence data, including variance-variance analysis, incidence-incidence analysis and test of goodness of fit for quadrat frequency. Preliminary results of these studies suggest the potential of three stages to the epidemiology of this disease in the field.
1. Initial infections result from the random introduction of virus airborne viruliferous mealybugs.
2. Vine-to-vine transmission by crawlers leads to aggregated disease foci developing around the initial infections (first 5 to 15 years). This phase may demonstrate an exponential increase in disease incidence, although further work is needed to justify this.
3. The typical plateau where the likelihood of a viruliferous mealybug coming in contact with a healthy vine is lowered, due to the high level of GLRaV-3 infected vines already within the vineyard block.
These three stages need better characterization in order to formulate future models and management practices on an area wide disease management level. A journal article on GLRaV-3 epidemiology is currently in preparation.
Area wide management groups have formed in Napa Valley, one in particular which we are currently working with hands on. Participants in this group are currently assessing adult male mealybug trap counts and the current status of GLRaV-3 incidence in vine blocks. Grower-collected data are collated and visualized via ArcGIS and GPS. Participants also attend meetings every month, where they discuss current control strategies, current mealybug trap counts, symptom expression, rogueing (removal of infected vines) and management success stories thus far. Other groups are also forming, some in connection to this group, others in response to presentations and outreach via grower conferences and personal contacts.
Future Work
With the formation of work groups, questions related to control can be better understood, answered and associated given these new lines of communication.  In order for GLRaV-3 regional control to be maintained, the following objectives must be fulfilled:
1. Epidemiological Study: Further characterization of the 3 potential stages of GLRaV-3 in the field to formulate future models and management practices on an area wide disease management level.
a. Sampling Calculator: utilize information gained from the epidemiological study to appropriate a potential online tool for use by growers for assessment of disease incidence in field with and without symptoms.
b. Economic Study: Based on information gained from the epidemiological study, financial values can be associated with the 3 stages of the field progression of GLRaV-3, assisting growers in better management decisions based in practice and economics by associating risk with GLRAV-3.


Wow, what a mouthful right?  What isn’t stated in the above description is the fact that these growers, who started the project, who participated in the studies, who are participating in the work groups, who are listening to the information and using it; these industry folks wanted to do something about leafroll (GLRaV-3, the one spreading around in fields).  Yet they felt powerless because neighborhood cooperation is a must in this situation, and quite frankly no one wants to be that guy, knocking on doors and telling people what to do (and quite frankly, no one listens to him, because he’s “that guy”).  This story’s big picture goes all the way back to simply knowing how to be a good neighbor, but with real life, financial consequences, and the desire and need for cooperation to be voluntary, NOT regulated by the law (or “that guy” who thinks he’s the law).  The UC presence gave these guys a chance to stand on neutral ground, discuss the issues, and start solving the problem, TOGETHER.  They are no longer powerless to this virus and it’s movement into their fields, because they are united and updated with shared success stories and management strategies–FROM WITHIN THE GROUP, this is not UC telling them what to do either.  We are merely present to answer questions and discuss matters that arise with a scientific background and understanding.

I think we could all take a little something from this in terms of society as a whole……so far, so good, that’s what.

Peruse the ‘Grapevine Leafroll Disease’ page for information on collaborators and other information on the topic.  Thanks for reading!


1. Alley L, Golino D. 2000. The origins of the grape program at Foundation Plant Materials Service. Proc 50th Annu Am Soc Enol Viticulture meeting, Seattle, WA. Am J Enol Vitic 51:222–30.
2. Gent, David H., Mahaffee, Walter F., McRoberts, Neil, and Pfender, William F. 2013. “The use and role of predictive systems in disease management.” Annual review of phytopathology 51:267-289.
3. Lubell, Mark, Hillis, Vicken, Hoffman, Matthew. 2012. “The perceived benefits and costs of sustainability practices in California viticulture.” Research Brief. Center for Environmental Policy and Behavior. Univ. of Cal. Davis.
4. Golino, D.A. and Almeida, R. 2008. Studies needed of vectors spreading leafroll disease in California vineyards.(pdf) Sidebar. California Agriculture 62(4):174.
5. Mannini, F., Aramante, N., Credi, R. 1996. Improvement in the quality of grapevine ‘Nebbiolo’ clones obtained by sanitation. Acta Hort. 427: 319-324.
6. Mannini, F., Argamante, I.N., Cuozzo, D., Credi, R. 2006. Modification in field behavior and grape quality, with focus on terpenes, after GLRaV-3 eradication in a clone of white muscat (Vitis vinifera L.). Extended abstracts 15th Meeting ICVG, Stellenbosch, South Africa, 3 –7 April 2006, pg. 136 – pg. 138.
7. Olmo HP. 1951. A proposed program for the introduction, improvement, and certification of healthy grape varieties. Wines Vines 32 (7):7–9.
8. Stephenson, W. 1954a. Comments on Cronbach and Gleser’s review of: The study of behavior: Q-technique and its methodology. Psychometrika, 19, 331-333.