Agriculture Reference
In-Depth Information
types are especially relevant to wine lovers,
since many of these not only look and behave
differently in the vineyards, but also give star-
tlingly different wines, even with similar wine-
making techniques.
Changes in genomes may occur via other
mechanisms: when a plant is moved from one
region to another, a modifi cation of its genetic
material takes place (“genetic drift”). Grapevines
do not remain the same in their new or fi nal des-
tination because at each stop they undergo
genetic introgression. Introgression is the intro-
duction into a genome of small portions of the
DNA of preexisting local species (cultivated or
wild) or of grapevine species they traveled along-
side (on a boat or a donkey, in a knapsack or a
box) en route to their new home. The grapevine
that fi nally “settles” for good in a new environ-
ment is no longer the same grapevine that left its
original home. Further, over centuries in its new
home the grapevine will undergo further
changes to its genetic and phenotypic makeup,
brought on by the environment, human selection
pressures, and other causes. Humans notably
prefer to propagate those grapevines with quali-
ties valued at that moment: resistance to disease
or copious productivity were most important in
our poorer past, while in today's more hedonistic
times better wine quality is the usual goal.
The end result of all this selecting, traveling,
and shuffl ing is that there are an estimated
eight thousand to ten thousand truly different
grape varieties used to make wine all over the
world today, though some report higher num-
bers of grape varieties when table grapes are
included. Italy, for a variety of reasons, has
more varieties than any other country: how this
came to be is absolutely fascinating.
CLONES AND BIOTYPES
Throughout the centuries, humans on the
move transported cuttings or buds from indi-
vidual grapevines they liked and replanted
them in new, suitable habitats even in distant
countries. In this manner there is no gene pool
shuffl ing, and each new plant is a genetically
identical copy of its parent, at least originally.
However, grapevines transported via cuttings
do not remain genetically identical to the pro-
genitor grapevine over centuries. This is true of
human beings too: according to Cavalli Sforza,
migration represents nothing more than a fl ow
of genes moving into or out of a gene pool to
create new genetic entities or modify preexist-
ing ones. Once reproductive cycles occur, there
is a reshuffl ing of the parental genes, and the
offspring will be genetically different from the
parents. At each cell division, errors can happen
and mutations are born. The ensuing grapevine
may look and behave essentially the same or
quite differently, exhibiting phenotypic plastic-
ity, defi ned as the range of phenotypes a variety
can exhibit due to its interactions with the envi-
ronment and humans (larger or smaller berries,
color differences, higher or lower yields, disease
susceptibility, and so forth). Though we habitu-
ally describe these new and different grapevines
as “clones,” this is incorrect, as clones are by
defi nition genetically identical to the mother
plant. It is more accurate to refer to these new
and different plants as biotypes. As we have
seen, biotypes express intravarietal variability,
the condition by which members of the same
variety will look different from others, or from
one area to another. These site-specifi c biotypes
often draw even experienced observers into
erroneous conclusions about their exact iden-
tity. Therefore, intravarietal variability is one of
the biggest causes of synonymity in wine
grapes, and of many erroneous ampelographic
attributions. Clearly, the more ancient a variety,
the more likely it is to have greater intravarietal
variability—and hence many biotypes—simply
because mutations have accumulated over
time. As I stated in the previous chapter, bio-
WHERE GRAPES GROW IN ITALY AND
HOW THEY GOT THERE
How did
vinifera
arrive in Italy? It's an important
question, for in the answer lies an explanation for
the country's myriad native grapes. Thanks
to the great body of work left us by the Russian
botanists Vavilov and Negrul, who studied the
