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Grape variety changes likely evolutionary, viticulture specialist says: Scions, rootstocks tested for SJV use

Can grape varieties such as Carmenere, Montepulciano, or Tempranillo offer something new and different to California wines? No one knows now, but University of California viticulturists are evaluating them, with a host of other Southern European varieties, for their performance in the San Joaquin Valley.

Jim Wolpert, chairman of the Department of Viticulture and Enology and viticulture specialist at UC, Davis, told growers at a symposium at Easton that any change in varieties will be evolutionary but the SJV will likely play an important role, since most of the tonnage comes from there.

Wolpert noted that although coastal counties enjoy wide consumer acclaim, they produce only about one-quarter of the tonnage of the state's crush, while valley counties make up the remaining three-quarters.

Trends in varietal changes are emerging, he said. Of the 36 red varieties listed in acreage statistics, nine (Cabernet Sauvignon, Merlot, Zinfandel, Pinot Noir, Syrah, Rubired, Barbera, Grenache, and Ruby Cabernet) make up 90 percent of the red wine grape acreage.

Since about 1995, Cabernet Sauvignon and Merlot have increased by 98,000 acres, or more than half the increase of all reds. Syrah has also gained, growing from 100 acres in 1982 to 14,700 in 2003.

“The story for whites is much simpler,” he said. Chardonnay acreage more than quadrupled from 22,000 acres in 1982 to more than 97,000 acres in 2003, while Chenin Blanc and French Colombard dropped sharply.

This, he continued, begs the question about a role for new varieties. “There's been an increase in total number of varieties on which statistics are now being kept, a total of 61 (36 red and 25 white). Many old and inferior varieties have been eliminated, not only from statistics but entirely from the field, and new ones, with better recognized quality have taken their place.”

Consumer claims

After interviews with industry leaders, Wolpert said he sees multiple perspectives in play. One is from consumers who claim they want something other than the big four of Chardonnay, Cabernet Sauvignon, Merlot and Zinfandel (red and white), even though the four continue to be the biggest sellers.

Growers have tended to embrace the idea of something new and support the study of new varieties from elsewhere in the world.

Winemakers have mixed opinions. Some, agreeing with growers, would like to see additional varieties, even though at the same time, they see marketing difficulties in getting consumers accustomed to spelling or even pronouncing new variety names.

Winemakers, Wolpert learned, are most interested in having a selection of new varieties that could be blended with the big four to produce wines more interesting and palatable to the public. “Varieties such as Italy's Aglianco and Montepulciano, or Portugal's Touriga Nacional,” he said, “might make a Cabernet more flavorful without the consuming public have to pronounce a new variety name or to understand its wine attributes.”

A current example of blending is Cabernet Sauvignon with Muscat of Alexandria for a wine with something different.

Variety trials

With that in mind, Wolpert joined with Davis colleagues and SJV farm advisors to set up initial trials in 2004 with 20 red European varieties at the Kearney Agricultural Center at Parlier. About 50 vines of each are planted.

“We want to do these trials right in the heart of the SJV at first and then later branch out to other locations.” The effort is funded by the USDA Viticulture Consortium and the American Vineyard Foundation.

Cabernet Sauvignon, Ruby Cabernet, and Syrah are included as standards well-known in the valley, along with new clones of both Grenache Noir and Durif (Petite Sirah), which also have been widely grown in the valley. From France are Carmenere, Petit Verdot, Malbec, Cinsaut, and Tannat. Italian varieties are Aglianico, Montepulciano, and Freisa. Tempranillo from Spain is known in the SJV as Valdepenas, but vines in the trials are new clones. The selections are rounded out with Tinta Amarilla and five other Portuguese varieties used for port production.

Wolpert said yield, quality, and growth traits will be monitored along the way, and he expects several of the first group will be dropped. Other varieties will be added if the grower and vintner community is interested in them.

Geneticists are also at work on the invisible components of a vineyard, the rootstocks that provide improved pest resistance, to match with future vineyards, whether planted to new or traditional varieties.

Symposium speaker Peter Cousins, grape rootstock breeder and geneticist with USDA-ARS at Geneva, N.Y., said he is working with other USDA scientists and University of California breeders to come up with rootstocks that are primarily resistant to aggressive rootknot nematodes.

The development and screening of potential new materials, funded mostly by USDA but also supported by California grape organizations, is done year round at Geneva and promising examples are brought to California for more evaluation. The process from initial selection to release of a final variety takes at least 10 years.

Their approach also is guided by selection of materials best suited to the San Joaquin Valley and other California grape growing regions and materials that are improvements on Freedom and Harmony rootstocks.

Rootknot focus

Cousins, a native of Ceres, Calif., and graduate of UC, Davis, said the focus on resistance to rootknot is because most of the grape acreage in the U.S. is in SJV counties and it is the primary pest in those locations. The removal of methyl bromide and restrictions on other nematicides, plus the nematodes' ability to develop new, more resistant forms, all further accentuate the need for new rootstocks.

“Rootknot nematodes are a triple threat to vineyards,” he said. “Not only do the knots they form reduce the ability of the vine to take up water and nutrients, they also remove water and nutrients that would have gone to the vine, and they provide an entry point for secondary pests and pathogens.”

Cousins challenges his new selections with populations of more aggressive rootknot nematodes collected by UC researchers from California vineyards. His task is to ultimately combine resistance to these populations, as well as common rootknot, with the desired horticultural traits of Freedom and Harmony.

Since laboratory-grown seedling selections made in New York are eliminated if they contain any rootknot egg masses, only 1 to 10 percent of the individuals advance to field testing in California. Cousins works with Duarte Nursery and other nurseries to speed up the process to observe horticultural traits.

“Our goal is to eventually supply materials for large rootstock trials,” he said. Plants grafted to Syrah and set out in the spring of 2005 in Fresno County and elsewhere in the SJV are the products of the past five years of screening he has done.

Wild grape sorting

Meanwhile, Cousins is sorting for rootknot resistance through a dozen wild grape species native to the eastern or southern U.S. and Mexico. He said he is using them to discover stronger resistance that will defend against the stronger populations brought about by years of use of Freedom and Harmony. In a matter of time, any new resistance from a different source will also encounter new, stronger nematodes.

“The way to keep ahead of nematodes is to keep identifying new sources of resistance. I'd like to say it doesn't mean having to switch over to new rootstocks, but I'm afraid it does. As nematodes are capable of evolving new resistance, we likely will have to switch to a different source for a different specificity.”

One eventuality to keep the pests off balance may be replanting and rotating through three rootstocks having different types of resistance, then returning to the first.

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