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Discovery could accelerate grapevine breeding

September 25, 2009  ByMarg Land


September 25, 2009 —
German researchers have uncovered new details about the heredity of Vitis
varieties in cultivation today through biomolecular detective work.



September 25, 2009 — One
of the best known episodes in the 8,000-year history of grapevine cultivation
led to biological changes that have not been well understood – until now.

Through biomolecular detective work, German researchers have uncovered new
details about the heredity of Vitis varieties in cultivation today. In the
process, they have opened the way to more meaningful classification,
accelerated breeding, and more accurate evaluation of the results, potentially
breaking a bottleneck in the progress of the wine industry.

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Their discovery removes a
major obstacle to a development already under way – that is, a shift toward
grapevine breeding guided by highly specific genetic markers. It may even point
the way toward production of European-tasting wines from North American
cultivars, free of the “musty” or “foxy” flavours associated with New World
grapevines.

In response to the great
European wine blight of the mid-1800s, growers aimed at preserving the most
desirable qualities of European grapes while breeding in the hardiness of North
American varieties. These were naturally resistant to native pests that had
found their way – by steamship, most likely – across the Atlantic to Europe.
Beginning around 1860, the introduction of two North American pests – an aphid
and a fungus – nearly destroyed the wine industry, particularly in France. A
century ago, many hybrids were in use, but the wine they produced was judged to
be so inferior in flavor that winemakers were prohibited from blending them
with higher-quality traditional wines.

Today, breeders as well as
growers have many reasons to want to know the heritage of grapevines, and
readily observed traits are seldom sufficient. To distinguish among the
countless grapevine cultivars, even experts need more than meets the eye. Much
of a plant’s history can be read on the molecular level, from its DNA and
biochemistry, and modern scientific tools have been developed to discern the
fingerprints of Old World, New World, and hybrid grapevines. New research
shows, however, that one of the best established fingerprinting tools is not
completely reliable, because it assumes a simpler genetic history than the
biomolecular evidence records.

The investigation was a
collaboration between the Technische Universität München in Bavaria and the JKI
Institute for Grapevine Breeding
, along the famous Weinstrasse (wine route) in
the Pfalz region. Clues led the researchers to suspect that a difference in a
particular phytochemical marker that has long been used to distinguish grape
varieties stemmed not from a single gene mutation, but from a double mutation.
Furthermore, they revealed, the chromosome bearing the double-mutated gene is
one that may also carry a gene responsible for the poor, “musty” aroma of the
North American varieties. A complex series of experiments and analyses
confirmed this, and ruled out other possible explanations. A detailed
description of the methods and results has been published in the Journal of
Agricultural and Food Chemistry
.

The biochemical process at
the crux of the investigation is the production of anthocyanin pigments. Red
European Vitis vinifera cultivars produce only pigment compounds such as the
one called oenin (malvidin 3-O-glucoside), whereas most other Vitis species and
hybrids can produce pigment compounds like malvin (malvidin 3,5-di-O-glucoside)
as well. This subtle difference, which has been used to classify wines
according to their varietal origin, had been attributed to a particular gene
mutation inherited by the European plants. If that was the whole story,
however, certain breeding programs might have been expected to turn on malvin
production in European varieties, and this had never been observed.

Professor Wilfried Schwab
of the Biomolecular Food Technology Department at TUM led the effort to find
out what genetic changes would restore malvin-producing enzymatic activity in
European varieties – with the primary aim of teasing out missing details of
their family history. The tools the investigators brought to bear included
techniques for isolating and cloning DNA sequences of interest, rewriting
specific parts of the genetic code – through what’s called site-directed
mutagenesis – and determining the three-dimensional structure of proteins
expressed as a result.

Their discovery of a double mutation could lead to the
development of more accurate classification tools and effective marker-assisted
breeding methods. They suggest that this knowledge might also be used in
another way, to enable American species and cultivars to produce
European-tasting wines, free of the “musty” or “foxy” flavours associated with
New World varieties.


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