What is certification and why is it important?
Certification is a system of monitoring and testing plants for the presence of undesired viral pathogens in combination with isolation and plant maintenance criteria. Initially you start with a plant, in this case a grape scion (or rootstock) that has been tested and determined to be free of viruses of concern. This plant is then the source of vegetative propagation to produce a planting stock.
Certification is essential in these woody perennial crops like grapes and fruit trees where you are planting for a generation. Grapes are susceptible to viruses that can reduce the quantity and quality of the crop - and are passed on down the line during the process of propagation. Without continued testing to confirm that propagation wood is free of viruses of concern, growers get the desired variety but also get any undesired viruses that may be present.
Once even a few infected vines are planted, insect and dagger nematode vectors can feed on infected vines and spread the infection throughout the vineyard. A few infected vines, over several years, can turn into a lot of infected vines. (see Grapevine leafroll virus: an increasing problem in the Finger Lakes, US, and the world)
Historically vineyards were started with cuttings from the vineyard down the road. These woody cuttings are collected in the early winter when there are no leaves present. This also means there were no visual symptoms of viruses present. Vines would be cut and propagated with no warning of the lurking viruses. Even with leaves, viruses can be present with no symptoms showing. Over time, this has led to significant dissemination of viral infections to new plantings.
Woody indexing – the traditional testing technology
Before molecular technology was developed over the past twenty years, the way to determine if a virus was present would be test it on “an indicator plant.” This is a process known as biological indexing where a plant that readily shows symptoms, if infected with a given virus, is used to indicate its presence. These plants include Chenopodium quinoa and some grapes including the rootstock Vitis rupestris St. George and the hybrid LN33, among several others. This was an effective technique for determining if viruses were present and still is today, but it is terribly time consuming. You have to allow time for the virus to develop in the indicator plant and for the plant to exhibit disease symptoms. You have to allow time for the plant to grow. Not to mention you need staff and facilities to grow, maintain and monitor them.
New molecular testing methods have reduced costs and delays
Marching forward, grape growers and nurseries asked to have New York’s certification program be brought back. Having this conversation in the 2000s is very different as the new molecular technology affords new opportunity. This means working smarter and in turn faster. Today we are using laboratory methods such as ELISA (enzyme-linked immunosorbent assay) and PCR (polymerase chain reaction) techniques that provide results that are better than the time-consuming biological indexing. Testing takes hours or days, not years.
The New York State Certification Program
New York’s program is nursery-focused. Nurseries bring in foundation, virus-tested, clean budwood (scion) and cutting (rootstock) material (called “G1” material) from Foundation Plant Services at UC-Davis in Davis, CA or the Clean Plant Center-Northwest at the University of Washington in Prosser, WA. These two clean plant centers maintain foundation (G1) vines and are part of the National Clean Plant Network (NCPN). Cornell University in Geneva is also part of NCPN but there is no G1 foundation vineyard in New York. The G1 vines are the “cleanest” of the “clean”, and many are derived from tissue-cultured material that was produced after therapeutic treatments to eliminate existing viruses.
Given the limited availability of G1 virus-tested, clean vines, nurseries need to bulk up this material to produce the desired planting stocks and respond to the growers’ demands. This is done in increase vineyard blocks (referred to as “G2 blocks”). Once in the New York nursery, the growers maintain the increase vineyard blocks planted with the G1 material in isolation from grapes that are not certified – both cultivated and wild. These G2 vineyard sites were screened for dagger nematode levels prior to planting to minimize spread of viruses vectored by nematodes. Insect pests such as mealybugs and soft scale insects are managed since they can vector leafroll viruses, and G2 vines are grafted on nematode-tolerant rootstocks.
Sample collection for virus testing
Staff from the New York State Department of Agriculture and Markets collect leaf samples for regular ongoing testing so that an increase vineyard block (G2) at the nursery is continually monitored catching any virus introductions before they are disseminated via propagation to the planting stocks sold by the nursery. New York has established a system to test 25% of all vines in the mother block each year. In the course of four years 100% of the vines in the mother block will be tested. At the nursery level, this represents the most frequent testing program in North America.
Samples for testing are submitted to Dr. Marc Fuchs’ virology lab at Cornell AgriTech, in Geneva, NY. Leaves arrive with just a sample number so that no one in the lab knows where the vines originated. Some viruses of grape are more readily detected in the spring (tomato ringspot virus, tobacco ringspot virus and grapevine fanleaf virus) versus the fall when grapevine leafroll-associated viruses and grapevine red blotch virus are optimally detected. Table 1 shows a list of viruses that are tested for and the timing of sample collection. Because of distinct optimal times for testing, samples are taken twice per year – once in the spring and then again in the fall. An increase vineyard (G2) is the endowment, the treasure to be protected. We monitor and test these vines to know they do not have viruses.
