DNA Testing For Grapes

[Barry S. Marjanovich]

DNA tests identify
grape names and
origins

WESTERN NOTEPAD

By Dan Bryant
Farm Press Editorial Staff

WILL THE REAL Petite Sirah please stand up?

Several California wine grape varieties have names different from
those used for the same varieties in Europe. This poses obstacles
to the California industry in drawing from the experience of
winemaking elsewhere in the world. Specifically, grape breeders
want to identify European varieties in their quest for traits that will
diversify the same varieties grown in California.

Now help is on the way to sort out the names and learn the origins
of varieties with sophisticated laboratory tests used by Carole
Meredith, a viticultural geneticist at the University of California,
Davis.

Examples of California varieties with other names in Europe, she
notes, are Zinfandel, or Primitivo in Italy; Napa Gamay, known in
France as Valdiguie; Grey Riesling, which goes by Trousseau in
France; Valdepenas, called Tempranillo in Spain; and Black
Malvoisie, the same as Cinsaut in France.

But we've all heard repeatedly that our Petite Sirah is just not the
same as Syrah, a black variety popularized in Australia in recent
years and now getting a closer look from the California industry.
Some have argued all along the two are the same. More about that
later.

New acreages of Rhone and other "new" wine varieties going in
up and down the state only add to confusion about what's what.

Need for identification

There are multiple reasons for correct identification. Government
regulations require that wines labeled a certain variety contain at
least 75 percent of that variety, our industry wants assurances that
imported wines are labeled correctly, and growers and vintners
must identify varieties to determine grape prices.

(I recall a veteran grape grower who could spot a variety from his
pickup passing a vineyard at 60 miles per hour. I've suspected,
however, that was really because he knew, over the years, what
his neighbors planted and where.)

Resolution of questions about varietal identification have been left
up to a few experts. These ampelographers can tell you the variety
by characteristics of berries and clusters, leaves, and shoot tips.
However, their observations are subjective and aren't surefire
accurate every time. Two ampelographers don't always agree.

Another shortcoming of ampelography, according to Meredith, is
there are too few who have mastered it and too many different
varieties. After years of study they can become proficient at
identifying maybe 10 to 20 varieties in their own region. That, she
adds, means an Italian ampelographer may really know his stuff
around home but isn't all that proficient with, say, Portuguese
grapes.

What's more, the berry color, leaf shape or cluster configuration
of the same variety can vary from climate to climate or when
disease is present.

Enter objectivity in the form of DNA typing. This is the same
"molecular fingerprinting" used by law enforcement to catch
criminals and by geneologists to trace family trees. Employing
DNA methods, Meredith has been doing some sleuthing regarding
grape origins.

At a recent wine grape symposium in Easton, she told San
Joaquin Valley growers, "When enough markers are used, every
grape variety can be distinguished individually, and in contrast to
ampelography, DNA characteristics do not change during the
growing season or when they are grown in different places or
when they are diseased. The DNA pattern remains the same."

A group of eight, crucial markers in DNA compounds, Meredith
says, can be relatively hard to find, but once they are located, their
reliability is high when checked against known varieties. Twenty
viticultural research groups in 10 countries are using the markers.

There is one hitch: the markers cannot at this time distinguish
between clones of a given variety, so researchers are still
challenged to sift out the clonal differences which Meredith says
undoubtedly exist.

Turning to investigations of other varieties, she said grapes from
the Plavac Mali area of Croatia long have been thought to be
related to Zinfandel because wines made from them taste the
same. Testing Zinfandel from the UC, Davis collection and Plavac
Mali samples, she found they were not identical but had strong
similarities.

She went to Croatia last spring in search of more information
about Zinfandel and the Italian Primitivo, thought to have come to
Italy from Croatia late in the 19th century, well after
documentation shows Zinfandel arriving in the eastern U.S.

Her analyses confirmed differences between the 150 Plavac Mali
samples she brought back and Zinfandel, but she also found DNA
similarities that suggest Zinfandel might be another, related
Croatian cultivar. That question may be settled with data from
additional samples.

She has also been on the trail of Petite Sirah. "Almost all Petite
Sirah is the relatively young French variety Durif, which is
reported to be a seedling of Peloursin, an older French variety.

"Our DNA results," she continued, "confirmed that Peloursin
could indeed be the seed parent of Durif, so we looked about for
the pollen parent and found it -- Syrah!

"So now the name Petite Sirah, criticized as a misnomer for a
variety that clearly is not Syrah, turns out to be rather appropriate.
Petite Sirah is truly the child of Syrah."

Meredith said she has identified the likely parents of more than 20
other varieties, including some important wine grapes. Results of
this work are pending completion of the analyses.

Vol. 21, No. 1, January 2, 1999