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The basic principle to apply when selecting winegrape varieties with which
to start a vineyard is to match the varieties to the climate. Texas
vineyards are located in all parts of the state, which encompasses a wide
variety of climatic conditions requiring varying considerations.
Temperature is the most important climatic factor and one of the concerns
in Texas is hot temperatures during the fruit-ripening portion of the
season. In many regions of the state, there are additional concerns over
potentially damaging cold temperatures in the dormant season and Spring
frost damage to young shoots.
Variety selection therefore, must consider the relative risk and impact
of unfavorable temperatures at a site in relation to the characteristics
of each variety. For example, "hot-climate" varieties that lack
adequate dormant-season cold hardiness have not been successful in west
Texas. Similarly, otherwise well-adapted varieties that have early
budbreak (e.g., Chardonnay and Sangiovese) can be a risky proposition in
areas that are likely to have late Spring frosts.
In a viticulturally hot climate such as Texas there is no shortage of
heat units or sunlight to ripen almost any variety of grape to adequate
sugar levels. However, the climatic conditions under which fruit ripening
occurs has a major influence on the speed of ripening, the development of
flavors, and the balance of sugar and acidity. Varieties that are
considered to be "cool-climate" types do not develop the same
flavors nor the balanced chemistry in a hot climate as they do under the
slow-ripening conditions of a cool climate. Therefore, varieties that are
known to perform well in a hot climate are the most likely to ripen their
fruit with good varietal character and produce high quality wines in
Texas. That being said, however, Texas has produced good wines from such
"cool-climate" varieties as White Riesling and Pinot noir grown
at higher elevations in west Texas.
Two other major considerations in choosing varieties for Texas
vineyards are market demand and, in some regions, resistance to Pierce's
Disease. Texas has already proven successful at producing good quality
wines of popular varieties. Presently, the top five varieties grown in
Texas are mostly well-known varieties: Cabernet Sauvignon, Chardonnay,
Sauvignon blanc, Chenin blanc, and Merlot. Port-style wines have also
received some recognition for high quality, as well as dessert-style
muscat wines made from Muscat blanc (Canelli) and Orange Muscat.
Production of varieties that are less well-known or unproven in the
marketplace can be risky, particularly if a high percentage of the wine
will be sold through distribution. However, small wineries that sell much
of their wine through the tasting room have the opportunity to introduce
customers to less familiar varieties, blends, and wine styles. Recently,
there has been considerable experimentation in Texas to evaluate the
commercial potential of varieties adapted to warmer climates, including
Syrah, Mourvedre, Grenache, Viognier, and Tempranillo. Some of these have
already made excellent varietal or blended wines, and increased experience
with them in the vineyard and winery should result in additional
improvement.
Variety evaluations have been conducted in various regions of Texas. A
12-year variety trial on the Texas South Plains concluded that the
varieties with the greatest potential for that region were: Cabernet
Sauvignon, Sauvignon blanc, Chenin blanc, White Riesling, Zinfandel, Ruby
Cabernet, Merlot, and Semillon. See the report Grape Cultivar Performance
on the Texas South Plains, 1974-1986 for more information on this
evaluation of 82 grape varieties. A new variety trial will be established
in 2003 at the Texas A&M Research Center in Lubbock. A good reference
book that provides descriptions of hundreds of varieties is Jancis
Robinson's Guide to Wine Grapes.
Pierce's Disease (PD) is of concern in many of Texas' grape growing
regions, but it is a limiting factor for production in areas close to the
Gulf of Mexico. Variety selection in high-risk regions quickly narrows
down to a few varieties that are known or thought to be resistant to PD.
The best PD-resistant white wine variety is Blanc Du Bois. Black Spanish
(also known as Lenoir) and Cynthiana (also known as Norton) are red wine
varieties with resistance to PD. Texas A&M University has a new
variety trial underway in College Station to evaluate varieties for PD
resistance or tolerance.
Varietal susceptibility to fungal diseases, particularly Botrytis Bunch
Rot, can be a consideration in high rainfall, high humidity locations.
Varieties with tight clusters (e.g., Chenin blanc and Zinfandel) are at
high risk for Bunch Rot in such regions.
Clones
A clone is defined (Hartmann, et al., 1990) as a genetically uniform
group of individuals derived originally from a single individual by
asexual propagation (cuttings, grafting, etc.). All grape varieties are
propagated by asexual means to preserve the unique characteristics of the
variety. But slight genetic variations commonly occur among the many
billions of cells that make up a grapevine. If a new vine is propagated
from a cane that grew out of such variant tissue, it may exhibit somewhat
different characteristics than the original vine. If the difference is
desirable, for example, the new vine ripens its fruit a week earlier, the
vine could be further propagated to perpetuate the new characteristics.
Thus, a new clone is born and it is assigned a number or given a name to
distinguish it from other clones.
In practice this means that there is more that one Cabernet Sauvignon.
One reference book lists 19 distinct clones of Cabernet Sauvignon (ENTAV-INRA,
1995) and describes their individual characteristics. To be considered a
distinct clone there must be a unique difference from other clones,
although sometimes the difference is slight. Keep in mind that differences
among clones of the same variety are vastly smaller than differences among
varieties, but sometimes the difference can be important. Clones may have
differences in time of budbreak, time of ripening, cluster architecture
(loose versus tight), fruit yield, fruit quality, or other
characteristics. In addition to the book by ENTAV-INRA, Caldwell (1998)
has produced a guide to winegrape clones.
It should be noted that the Foundation Plant Services (FPS) in
California assigns unique numbers to different selections of the same
clone that have undergone various virus elimination treatments.
References
Caldwell, J. 1998. A Concise Guide to Wine Grape Clones for
Professionals. Second Edition. John Caldwell Viticultural Services. Napa,
California.
ENTAV-INRA. 1995. Catalogue of Selected Wine Grape Varieties and Clones
Cultivated in France. Ministry of Agriculture, Fisheries and Food. CTPS.
Hartmann, H.T., D.E. Kester, and F.T. Davies, Jr. 1990. Plant
Propagation Principles and Practices. 5 Edition. Prentice Hall. Englewood
Cliffs, New Jersey.
Robinson, J. 1996. Jancis Robinson’s Guide to Wine Grapes. Oxford
University Press. New York.
Additional Resources
National Grape Registry
University of California Agriculture and Natural Resources, FPS, NCGR, and
USDA-ARS
The National Grape Registry (NGR) contains information about varieties
of wine, juice, and table grapes, raisins, and grape rootstocks available
in the United States. Growers, nurseries, winemakers and researchers can
find background information and source contacts for those grape varieties
in this single convenient location.
Vitis International Variety
Catalogue
German Centre for Documentation and Information in Agriculture
The Catalogue provides details of grapevine collections in 126
institutions, on disease resistance data (with bibliographic references),
characterization data (photographs, berry and shoot descriptions, seed),
and passport data (prime names, synonyms, pedigree, holding institute).
Plant
Genetic Resources Unit
USDA-ARS and Cornell University
Vitis, or grape, is one of the large collections at the PGRU. Over 1800
separate accessions of grape are held under commercial field conditions at
the Clonal Repository Farm located a mile north of the station.
National
Clonal Germplasm Repository for Fruit and Nut Crops at Davis, California
USDA-ARS
The NPGR for Fruit and Nut Crops is one of over two dozen facilities in
the National Plant Germplasm System which collect, maintain, characterize,
document and distribute plant germplasm from all over the world.
FPS Grape
Program
Foundation Plant Services (FPS) was established as a public service
unit at the University of California Davis to maintain and distribute
materials from Foundation collections of grapevines as well as several
other vegetatively propagated crops.
European Vitis Database
The establishment of an european grapevine genetic resources database
with free access via Internet is one of the objectives of the European
Project GENRES #81. The aim of the database is to enhance the utilization
of relevant and highly valuable germplasm in breeding.
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