Download What is a grape variety? excerpt from “The evolution of wine grape

What is a grape variety?
excerpt from “The evolution of wine grape varieties”
Arunda 83 “Rebsaft”
Dr José Vouillamoz, Switzerland
Throughout the evolutionary history of the grapevine, every single grape variety is the result of a
single vine grown from a single seed, and this seed is the result of a sexual event that took place
between two parent varieties (Figure 5). Several parameters have to be fulfilled for the
spontaneous birth of a new grape variety:
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a flower in a grape bunch has to be fertilized for a berry to be formed
the bunch must not be harvested
the berry must fall on the ground or be eaten and carried away by an animal
the pip must germinate and grow into a seedling
the seedlingmust not be dug up
the plantlet has to survive for at least three year to bear fruits and to be identified by a
human eye as an interesting grapevine
the plantlet has to be propagated vegetatively for all its lifespan
Until the end of the 19 th century, all the vineyards in the Ancient World were intermixed with
several grape varieties planted without real structure, so that crossings between distinct varieties
could happen all the time and new vines were free to grow. This spontaneous birth of new
varieties has become almost impossible in modern, regimented, monovarietal vineyards, where
self-pollination is far more common and where every new plantlet would be torn out. As a
consequence, the natural evolution of grape varieties has almost come to a dead end, and since
the 19 th century it was replaced by artificial crossings made in breeding research centres.
Figure 5. How does a new grape variety appear? Every grape variety is the result of sexual
reproduction.A grape variety is defined as the group of morphologically distinct clones developed
during vegetative propagation via cuttings and derived from a single seed born from two parent
varieties.
When one of the billiards of grape pips produced by selfing every year on the planet is planted,
the seedling represents a new and distinct variety that is highly consanguineous with the mother
plant (inbreeding), which is why selfing has never been favoured by human hands, simply because
the resulting plants are usually degenerative and more susceptible to diseases. The enormous
genetic diversity observed among grape varieties (Aradhya et al. 2003; Cipriani et al. 2010; Myles
et al. 2011)sounds like evidence that cross-fertilization has prevailed for the origins of the ca.
10000 in existence today, with the combination of distinct genomes leading to more distinctive
and interesting new varieties thanks to the apparition of new traits. Additional new traits may then
appear as a result of mutations.
Mutations
Once a new variety has been selected, it is vegetatively propagated by cuttings or layering in order
to maintain the desired morphological and organoleptical traits. At each cell division during plant
growth, errors are likely to occur when DNA is replicated: these errors are spontaneous mutations.
The vast majority of these mutations affect non-coding portions of DNA (over 90% of the DNA of
higher organisms has no known biological function; also referred to as "junk DNA") and have no
effect on the plant. The mutation rate in coding DNA (genes) of higher organisms is roughly one
mutation per 300 cell divisions (Drake et al. 1998). After decades or centuries of vegetative
propagation, each grapevine plant harbors hundreds of thousands of new mutations. Most of them
will go unnoticed, and only those affecting berry size or colour, cluster size, leaf shape, ripening
period or any other effetthat is ‘spectacular’ to the human eye will be noticed and propagated
separately. However, as spectacular as the morphological change can be, the accumulation of
mutations over time do not result in new grape varieties, these are only clones of the variety.
Therefore, a grape variety can be defined as a group of morphologically distinct clones originating
from a single initial seed, which was sexually produced by a father variety fertilizing a mother variety
(Boursiquot and This 1999) (Figure 5). The older a variety is, the higher will be the number of its
clones. For example, Pinot has hundreds of clones simply because it is very old, and not because
it would be more prone to mutations than other varieties, as it has been mistakenly suggested
(Bernard 1995). Pinot Noir (black-berried), Pinot Gris (grey- or pink-berried) and Pinot Blanc (whiteberried) are often considered as distinct varieties, but they are nothing else than skin colour
variations of the same variety, as a result of a particular type of mutation: the insertion of a
transposon (or ‘jumping gene’) in the DNA region that regulates a gene responsible for anthocyans
synthesis (called VvmybA1) causes the loss of black berry skin colour (This et al. 2007). Pinot Noir,
Pinot Gris and Pinot Blanc are undistinguishable by DNA profiling, and are therefore considered
one and the same variety.
Founder varieties
Since every individual (grape, human, etc.) receives half of its DNA from his father and half from his
mother, DNA profiling is also useful for the reconstruction of parentages (paternity test) and
pedigrees, which requires between 20 to 60 microsatellites to be analysed for statistical
confidence. The first successful paternity test was realised in 1997 when Professor Carole
Meredith and her doctoral student John Bowers at the University of California in Davis have shown
that Cabernet Sauvignon, the noble Bordeaux grape variety, was most likely derived from a natural
cross between Cabernet Franc and Sauvignon Blanc (Bowers and Meredith 1997) (Table 1).This
came as a big surprise to the wine world.
Since then, the study of the relationships between grape varieties has entered the new era of
‘historical genetics’, with the discovery of several subsequent and unexpected parentages (see
Sefc et al. 2009 for an overview). Uniparental parentages were then successfully studied: when
one of the parents is missing (ie not yet analysed or extinct), it is still possible to detect parentoffspring relationships between two varieties when they share at least one value at each
microsatellite, which has been shown to require a minimum of 50 to 60 microsatellites to be
statistically proven (Vouillamoz and Grando 2006). However, it is not possible to determine which
one is the parent and which one is the progeny, simply because the age of a variety is unknown.
When both parents are missing, the use of a recently developed probabilistic approach has
detected unsuspected brothers, half-siblings, grandparents or grandchildren in the complex
pedigree of Syrah (Vouillamoz and Grando 2006).
Table 1. In 1997, Cabernet Sauvignon was unexpectedly found to be the natural progeny of
Cabernet Franc and Sauvignon Blanc.At each of the 32 microsatellite that were analysed, Cabernet
Sauvignon obtained one value from its father (Cabernet Franc) and one value from its mother
(Sauvignon Blanc).
Cabernet
Franc
Cabernet
Sauvignon
Sauvignon
Blanc
Microsatellite 1
184-164
164-158
158-152
Microsatellite 2
191-179
191-171
191-171
Microsatellite 3
234-232
244-234
244-238
Microsatellite 4
197-197
197-191
191-191
Microsatellite 5
155-137
157-137
157-129
Microsatellite 6
220-214
222-220
222-212
etc.
…
…
…
Table 2. Most grape varieties cultivated today in western Europe seem to descend from a small
group of founder varieties through spontenous crossings.
Founder
varieties
France
Italy
Croatia
Spain
Alps
Pinot, Gouais
Garganega,
Tribidrag
Cayetana
Rèze
Blanc,
Nebbiolo,
Savagnin,
Teroldego,
Cabernet
Luglienga
Franc,
Bianca,
Mondeuse
MuscatBlanc
Noire
à PetitsGrains
Blanca
After 15 years of pedigrees reconstruction, it appears that a limited number of founder grape
varieties gave birth by spontaneous crossings to a large number of progenies that represent the
grape germplasmof Western Europe today (Table 2). Cabernet Franc is one of them: besides
having given birth to Cabernet Sauvignon, it is also the parent of two other Bordeaux varieties,
Merlot and Carmenère (today more widespread in Chile and China than in its homeland). But the
most important founder variety seems to be Gouais Blanc, an almost forgotten grape that used to
be widespread all over western Europe in the Middle Ages : it is the parent of no less than 80
grape varieties, like Riesling from Germany, Chardonnay and Gamay from Burgundy, Furmint from
Hungary, Blaufränkisch from Austria, etc. Savagnin, known under different names and forms
(Traminer, Gewürztraminer, GelberTraminer, Savagnin Rose, etc.), has also significantly influenced
the western European viticulture by giving birth to varieties as diverse as Sauvignon Blanc and
Chenin Blanc from the Loire, Verdelho from Madeira, GrünerVeltliner from Austria, etc. Pinot,
without colour distinction, comes not far behind, having engendered Chardonnay and Gamay in
Burgundy, and possibly Savagnin itself.
There are several other founder varieties in western Europe (Table 2), and future studies on the
pedigrees of grape varieties from all over the Ancient World will undoubtedly identify many other
founder varieties for each region, providing a much better understanding of grape varieties
evolution.
Photo: The author José Vouillamoz (right) together with Patrick McGovern (left) infront of a wild
grapewine on the shore of the headwaters of the Tigris River in south eastern Turkey (photo: Ali
Ergül)
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