Jorman Heflin | 08-01-2020
Tags: chalk talk
What are varietal clones, why are they useful, and where can you get them?
Grapevines grown from seed are not phenotypically similar to their parents. This is because grapevines have a highly heterozygous genome that prevents self-pollinated plants from breeding true. New vines are grown from rooted cuttings, which are genetically identical 'clones' of the parent vine. As the parent vine ages, a mature clone is chosen to replace it as the source of new cuttings, and so the cycle repeats. Clonal propagation of grapevines has occurred in this way for centuries. Over many generations, clones accumulate genetic mutations due to selective pressures and random errors in DNA replication. These mutations create subtle variations in things like leaf shape, berry color, ripening time, and disease resistance. As a result of these mutations, the same variety of grapevine (e.g. Cabernet Sauvignon) may display slightly different phenotypes, depending on the source of the clone. Vines in two vineyards started from clones of the same parent vine in the 1800's will have accumulated small differences in character over the past 200 years. Plants in these vineyards today are the same variety, but may have slightly different phenotypes1. Classifying and maintaining these distinct clones is useful because some clones may be better adapted to grow in certain climates, or be better equipped to handle local disease pressures.
In 1958, the University of California, Davis, set up Foundation Plant Services (FPS) to characterize and maintain varietal 'selections'. Selections are cuttings taken from a single source vineyard. These cuttings are shipped to FPS from vineyards all around the world. Each selection does not necessarily constitute a phenotypically distinct clone. Of the 66 Cabernet Sauvignon selections available, there may be about 10 distinguishable clonal groups. FPS maintains a vineyard full of many different selections, and distributes cuttings from these plants to nurseries all over the world. I use ‘FPS 04’, which is a popular Cabernet Sauvignon selection used by many high end wineries. It came to FPS in 1964 from a vineyard in Mendoza, Argentina.