UC staff member Jorge Osorio Aguilar weighs grapes from a Syrah clonal selection under test for San Joaquin Valley conditions.

UC staff member Jorge Osorio Aguilar weighs grapes from a Syrah clonal selection under test for San Joaquin Valley conditions.

To a grower, the right wine grape clone can improve yield, advance or delay ripening, and reduce susceptibility to rots. For a winemaker, the right clone can add complexity to the wines. But with so many clones of a given cultivar available, how do you choose? And, with the performance of clones so dependent on the growing region, how do you choose the best for your site?

In the area of clonal research, the United States lags far behind Europe. Clonal research takes big dollars and years of commitment to collect and analyze vine, fruit, and wine data. Washington State’s wine industry has scant university data about which clones do best here and must draw on private research and data from similar ­growing regions.


The first Riesling wine grape clone was planted in Germany in 1930, said Dr. Ernst Ruehl, grape breeder at Geisenheim Research Center in Germany. Ruehl, who has been involved with clonal research at Geisenheim, spoke at the annual meeting of the Washington Association of Wine Grape Growers held in Kennewick.

The word “clone” means twig or branch in Greek. Ruehl defines a clone as the vegetative offspring of a single mother plant.

“The idea is that if you multiply one plant vegetatively, then all of the offspring will have identical genetics and the same management demands. A clone is a way to increase uniformity in the vineyard,” he said, adding that uniformity is essential for good vineyard management. “Without clones, you struggle with vineyard ­management.”

Clones result from mutations in which only a small part of a gene has been changed, Ruehl said. The vine may show small or large variations, depending on which gene and where the change takes place. These mutations can show up as differences in leaf shape, berry color, shoot development, ripening, cluster structure, and fruit composition, for example. Pinot Gris, a white wine grape, is a clone of the red grape Pinot Noir, discovered when berries of two different colors were found growing on the same vine.

Europe is home to most clones because the vineyards and varieties have been around for centuries, allowing more time for genetic variations to occur. Pinot Noir, one of the older varieties, has more clones than any other variety, Ruehl said.

Years and years

The search for new clones is long and tedious. After Ruehl and his colleagues identify potential candidates from old vineyards or Geisenheim’s breeding program, cuttings are screened for viruses and clean selections planted at the research station. Then, years of data collection begin. Researchers gather information on vine and berry attributes, along with sensory and chemical wine analyses. The clone must be new and unique from other clones before it can be registered.

Ruehl said he has been collecting data on clone candidates for more than ten years, and has yet to make wine in large enough quantities for evaluation, a vital part of clonal assessment.

“What makes a good clone is one that makes good wine,” he said, adding that they have not yet reached the wine ­analysis part of the clonal research.

California perspective

Matthew Fidelibus of the University of California’s viticulture and enology program has been working to help California’s San Joaquin Valley grape growers choose clones that will optimize yield and fruit quality. The San Joaquin Valley wine grape industry is based on high-volume, high-quality, low-cost production, he said.

Fidelibus began research in 2000 on Barbera clones, looking at yield, fruit composition, rot susceptibility, and wine quality. Barbera, an important cultivar to the San Joaquin Valley, is used mainly for blending. About 7,500 acres have been planted in the state; 90 percent of production comes from the San Joaquin Valley. But with almost a dozen Barbera clones registered by the Foundation Plant Services at UC, Davis, (three recently available from Torino, Italy), growers didn’t know which clones would do best in the San Joaquin Valley. Through the years, he has widened his clonal trials to include ­Cabernet Sauvignon, Merlot, Zinfandel, and Chardonnay.

Clonal research in California began in the 1950s to identify productive clones of Chardonnay, he said, noting that UC researchers found that yields could be increased up to 5 tons per acre, depending on the choice of clone. Through the years, clonal research has taken place in spurts, often based on the personality of the individual that was leading the research, he said.

Dijon or Fresno

Technically, all propagated vines could be considered clones because they were asexually propagated from mother vines, Fidelibus said. But clones are of interest because they have a distinct characteristic that sets them apart from the main variety. However, climate can change the way clones behave. “You may find that a clone performs really well in Dijon, France, but performs poorly in Fresno, California.”

In his Barbera clonal trial, he found that out of five clones, the FPS 2 was the worst choice because of rot problems, while FPS Barbera 6 was the best choice for San Joaquin Valley growers. Cabernet Sauvignon clones 8, 21, and 22 had the highest yields, while 22 and 24 were the earliest maturing,  and clone 2 was the latest maturing. No differences in anthocyanins have been observed.

For Chardonnay, clone 15 has potential for growers because of the greatly reduced rot from looser and more open clusters. Merlot clone 10 has performed well in his trials, with high yields, low pH,  and high titratable acidity.

He is comparing several Australian Shiraz clones to Syrah clones from the French INTAV-ENRA plant breeding program. Preliminary data show the Shiraz clones to be better suited for San Joaquin Valley growing conditions than the clones from France.