By: Judit Monis, Ph. D.
As I write this article, the world is experiencing the SARS-COV-2 pandemic responsible for causing COVID-19 disease. Generally, I find it difficult to explain quarantine measures. Today, I am sure that all of my readers might had practiced some sort of “sheltering in place” or “social distancing”. Therefore, the concept of quarantine will feel closer to home at this time. I am revisiting the quarantine and certification topic as this time; it is expected that my audience will be more receptive to the concepts.
Years ago, when I worked at the United States Department of Agriculture – Animal and Plant Health Inspection Services- Plant Protection and Quarantine (USDA APHIS PPQ), my group learned about the interception of citrus cuttings (intended for planting) that were packed pretending a box of chocolates was in the shipment. I am sure that you have heard before about “suitcase clones”. These are grapevine clones that people have brought from abroad before or after quarantine measures were developed It is my hope, that what we learned about the introduction and spread of SARS-COV-2 world-wide will provide a lesson to people to think twice before breaking the law by introducing plant material without import permits or respecting quarantines.
Plant quarantine programs have been developed worldwide to reduce the risk of introducing plant pests and/or pathogens that do not occur in a country or region. My expertise is plant pathology and throughout my career I have specialized in the study of bacteria, fungi, and viruses that affect the vineyard and fruit orchards. In spite of the current existence of plant quarantine programs, all grapevine pathogens with rare exceptions occur in all grape growing areas worldwide. The reason for this is that in most cases, quarantine programs were implemented after the introduction of the infected plant material. In addition, modern techniques for the detection of these pathogens were developed after the plant material was introduced. In other words, the majority of grapevine pests and pathogens were moved unknowingly.
The advancement of science and the use of sophisticated detection methods for grapevine pathogens has helped keep certain viruses outside of Australia. For example, Grapevine fanleaf (GFLV) and Grapevine red blotch viruses (GRBV) have not been reported in Australia as of yet. But even now with the use of advanced methodologies, pathogens continue to be discovered. As science progresses with the development of more refined technology (e.g., next generation sequencing also known as high throughput sequencing), it is expected that new (or unknown and established) pathogens will be discovered. In practice, most grapevine pathogens have originated at the centers of origin of the Vitis (a plant genus that includes both table, wine, and rootstock grapevine varieties) species and moved to many grapevine growing regions in the word when plant material was introduced.
In the United States, the USDA APHIS PPQ regulates the introduction of plant material for planting from foreign countries. However, the USDA does not have a centralized government plant quarantine system. Instead, APHIS issues permits to specific clean plant centers with proper containment facilities and approved protocols to manage the quarantine of specific crops. For grapevines, two import centers are available for introducing quarantined planting material: The Foundation Plant Services (FPS) at the University of California at Davis and the Clean Plant Center at Cornel University in Geneva, New York.
Since pathogens are present in most grapevine growing areas, certification programs are needed to produce tested plant material that is free of known important pathogen. These plants are be distributed to nurseries that further propagate and sell them to growers. In the United States, certification programs are voluntary and are managed by individual states. I am most familiar with the certification program in California, and many US grapevine growing regions purchase planting material from California nurseries.
The Grapevine California Registration and Certification (R&C) Program was first written into law in the 1980’s. The Grapevine R&C Program is administered by the California Department of Agriculture (CDFA) and provides for the testing of source vines for grapevine viruses that cause important diseases. Registered sources and certified nursery stock are periodically inspected by the CDFA staff and are maintained by the participant nurseries. Starting in 1996, I participated and provided input at the industry meetings that lead to the revision of the California Grapevine R&C program many years later. In 2010 the Grapevine R&C program was revised to include testing of foundation mother vines for the presence of a comprehensive list of viruses. With funding from the National Clean Plant Network, a new of foundation block “Russel Ranch” was started at the University of California at Davis in 2009.
The planting material (both scion and rootstock varieties) included in the new foundation block had to pass a rigorous testing program and have been propagated using the “apical micro-shoot tip culture” technique. The apical micro-shoot tip culture process is a plant tissue culture technique that is used to eliminate pathogens from vegetative propagated plant material. The testing program is known as Protocol 2010. The maintenance and testing of the scion and rootstock mother blocks are performed by UC Davis FPS personnel. Shortly after the update of the California Grapevine R&C Program, GRBV, a virus of significant importance for the vineyard industry, was discovered. Consequently, the California Grapevine R&C Program was revised again to include the testing of foundation and nursery increase blocks for the presence of GRBV.
The California Grapevine R&C Program rules can be found in CDFA’s website: https://www.cdfa.ca.gov/plant/pe/nsc/nursery/regcert.html
The testing of the foundation mother plants includes a list of well characterized viruses, Xylella fastidiosa, and phytoplasmas using biological, serological, and molecular testing techniques (https://fps.ucdavis.edu/fgr2010.cfm). The nursery increase blocks are inspected and tested by CDFA personnel. The nursery increase blocks are only tested for GFLV, Tomato ring spot (ToRSV), and Grapevine leafroll (GLRaV)-1and -3 using the Enzyme linked Immuno assay (ELISA). The updated Grapevine R&C added the testing for the detection of GRBV using the polymerase chain reaction (PCR) to vines in the foundation and nursery increase blocks.
Unfortunately, other insect vectored viruses such as GLRaV-4, Grapevine virus A (GVA), GVB are not being tested at the nursery. Related to nursery certified plants, the rules are vague and state that these plants may be tested (particularly if after inspection suspected symptoms are observed).
According to CDFA, the goal is to test a statistical sample with a 95% confidence level assuming a 1 % disease incidence. It is disappointing that in spite of the importance of the decline and canker diseases caused by fungal pathogens (and how easily the pathogens can be transmitted by activities carried out at the nursery), the regulations do not include inspection or testing for fungal pathogens in mother or increase blocks.
In the past few years, the Russell Ranch foundation block became progressively infected with GRBV. The infection status is so high that last year FPS suspended the sale of plant material to nurseries. I will not elaborate on this issue as I have recently written about this topic.
Obviously, in spite of the limitations of the R&C program mentioned above, the use of certified material is expected to be less risky than planting field selections of unknown infection status. However, it is always prudent to consult with me to assure that the planting material meets the expected cleanliness standards.
An important piece of advice when working on the procurement of clean planting stock is to plan in advance. Most nurseries in California collect cuttings for bud wood as soon as the vines are dormant. However, grafting activities are performed during the spring of the following year. Planning with time will allow for inspection of the increase blocks early in the fall before a freeze. Being familiar with the nursery’s operations and their staff is important. Good communication will help with scheduling inspections and testing of the increase blocks from which bud wood and rootstock cuttings will be collected.
Diseases, pathogens, and/or their vectors do not know or respect the borders between vineyard blocks (at the nursery, foundation block, or your vineyard). Even if the planting material came from a reputable certification program, paying attention to the surrounding vineyards as well as having knowledge of the potential presence of disease prior to planting is important.
The planning of a new vineyard is not trivial and requires specialized knowledge. I am available to help look for suspicious symptoms (inspect scion and rootstock source blocks), evaluate the planting site, develop a testing plan based on science and statistics, and review nursery and vineyard disease testing history.
Judit Monis, Ph.D. provides specialized services to help growers, vineyard managers, and nursery personnel avoid the propagation and transmission of disease caused by bacteria, fungi, and viruses in their vineyard blocks. Judit (based in California) is fluent in Spanish and is available to consult in all wine grape growing regions of the word. Please visit juditmonis.com for information or contact firstname.lastname@example.org to request a consulting session at your vineyard or virtually.