Identifying Varieties and Clones by DNA Typing

In 1997 we conceived and founded the Vitis Micro satellite Consortium, a group of 18 cooperating grape research groups in 10 countries that are sharing the costs and labor to develop 100 to 200 new grape SSR DNA markers. Although we already have enough DNA markers for routine grape variety identification, these additional markers will be used for genome mapping and may also be of value for distinguishing closely related varieties and possibly for identifying clones. We were not able to initiate a proposed new approach to clone discrimination until late in the 1997-98 period because of insufficient funding but will actively pursue this avenue during 1998-99. Our cultivar database has continued to grow and now contains 111 cultivars that have been typed with 13 to 18 DNA markers. This geographically balanced database not only provides us with references against which to compare unknowns, but is also the basis for estimating the statistical probability that a DNA-based identification is correct. We have also developed a database of 300 French cultivars that we will keep separate for statistical purposes so as not to bias the original database geographically. This database will be useful for verifying the identity of new French vine importations and for identifying unknowns in California vineyards (see Carmenere below). In order to continue to investigate the hypothesis that Zinfandel is the Croatian variety Plavac Mali, we obtained three accessions of this variety from the Croatian island of Brae. As we had earlier found with two Plavac Mali accessions growing in our UC Davis collection, none of these three is identical to Zinfandel. They are, however, very closely related to Zinfandel. We now know that the variety Plavac Mali is not genetically uniform and contains several related sub-types. (We have detected three.) We think that we have not yet seen all the Plavac Mali sub-types and that analysis of additional Plavac Mali samples is warranted. If Zinfandel is found in Croatia, then we may have a source of needed clonal diversity for California Zinfandel. If Zinfandel is not found, then any attempts to market Croatian Plavac Mali wine as Zinfandel can be countered with strong scientific evidence. In collaboration with a visiting Chilean researcher, Dr. Patricio Hinrichsen, we investigated the identity of some vines in Merlot vineyards in Chile that have been identified ampelographically as the old Bordeaux variety Carmenere, as well as an FPMS vine originally labeled as Cabernet Franc but also suspected to be Carmenere. All were confirmed as true Carmenere by comparison to an authentic DNA reference obtained from Montpellier France (see French database above).