Identifying Varieties and Clones by DNA Typing
DNA marker development is now complete. Of the 29 markers we have developed, 15 are sharp and informative enough to be used for cultivar identification. In addition, we can use several markers developed in Australia. This is more than enough to identify any grape cultivar. Our database of cultivar profiles now contains DNA types of 77 cultivars for 8 DNA markers. The database is essential not only as a reference for identification but also to provide the statistical foundation necessary to validate this method. The database must now be expanded to include all of the 15 best markers and a larger number of cultivars. Since the group of 77 cultivars that we have so far analyzed contains a disproportionately high number of French wine grapes and Greek table grapes, additional cultivars will have to be added to make it more representative and thus more accurate. We had originally hypothesized that SSR DNA markers might be able to distinguish clones. After surveying 15 Chardonnay clones, 15 Pinot Noir clones and single-vine samples from a century-old Zinfandel vineyard, we have detected only one DNA difference in one Chardonnay clone. This leads us to think that SSR DNA differences among clones are more rare than we originally hypothesized. Our results suggest that SSR DNA markers could distinguish clones, but that a much larger number of markers would be required than we now have. Such a large number of markers would be very expensive to develop (but not to use) and thus might not be practicable. We are now investigating another DNA-based approach, AFLP analysis, that has promise for identifying clones.