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Breeding,
generally spoken, is aiming at the improvement of crop plants e.g. for yield,
product quality, specific resistances etc. Considering grapevine breeding some
peculiarities need to be reminded. Grapevine is a vegetatively propagated,
perennial crop, highly heterozygous, suffering from inbreeding depression,
yielding fruits to be used either as table grapes or for wine making. Varieties
like the Pinots, Chardonnay, Riesling, Cabernet Sauvignon, Merlot and many
others are considered to be of outstanding wine quality, provided they are
grown under suitable conditions and winemaking is done accordingly. Thus,
genetic improvement of wine grapes is mostly focused on viticultural traits
(input traits) since quality of existing varieties and yield are sufficiently
good. Consequently, resistance characteristics are the most desired traits to
be improved since grapes need very intensive and strict plant protection measures,
particularly against fungal diseases. This is confirmed by a study of the
European Union which shows that the use of fungicides in viticulture is
considerably higher compared to all other crops
(Figure 1)
. Concerning ecological
aspects this substantial impact of pesticides is to be seen critically.
Moreover from the point of public perception in western countries application
of fungicides and pesticides is somewhat delicate. Additionally to ecological
reasons this is also of high importance from the economical point of view.
Depending on the degree of resistance of individual varieties and hence on the
decrease of plant protection measurements up to 696,- € per hectare and year -
which is about 15% of the total production costs can be saved by using varieties
with fungus resistance characteristics (Table 1).
Efforts
to improve vines by breeding are rather old and it is worthwhile to reflect
briefly the history in this area.
Grapevine Breeding: drawback and success
The
beginning of grapevine breeding activities can be traced back to the second
part of the 18th century when phylloxera and the mildews (powdery and downy
mildew) were dragged into Europe from North America. When the French scientists
Bazille, Sahut and Planchon discovered in 1868 for the first time phylloxera on
the roots of grapes they surely could not imagine that this discovery was the
beginning of the end of a several thousand years old viticulture. Particularly
in France phylloxera led to tremendous damages and the living of thousands of viticulturists
was endangered. It was Millardet in 1880 who stated that it should be possible
to combine the resistance features of the American wild species with the
quality features from the European Vitis vinifera cultivars. In Germany it was
Baur in 1913 who encouraged the officials to initiate breeding activities for
resistant grapevines.
At the
beginning, breeding programs mostly covered both phylloxera and the mildew
resistances, aiming at an "ideal vine". But very soon a separation
between phylloxera resistance (rootstock) breeding and fungus resistance
breeding could be observed.
In
retrospect, rootstock breeding led rather quickly to good and sustainable
results. Thus, today´s European viticulture is almost exclusively based on
phylloxera-tolerant rootstocks developed about 100 years ago by breeders like
Richter, Paulsen, Kober, Teleki and others. Consequently, the introduction of
graftings was an important fact if not the factor for a survival of European
viticulture (see Figure 2).
Breeding
efforts for fungus disease resistance were not equally successful, though
resistant varieties have been obtained. Even after decades of intense breeding
work the quality characteristics of the new varieties, except those obtained by
the end of the 20th century, did not at all fulfil the expectations. One of the
major reasons is that resistance from wild species and quality as well as
agronomic performance from Vitis vinifera varieties cannot be combined in a
single or within a few breeding steps (for breeding goals and breeding
strategies see Figure 3). Due to the polygenic nature of both characteristics,
resistance (agronomic performance) and quality, several back-crosses are
necessary in order to achieve a sufficient resistance level and high wine
quality. The time consuming generation- and evaluation-cycles revealed that
many breeders, especially the private breeders in France - though quite
successful - gave up (see Fig 2). The varieties introduced during the first
part of the 20th century showed in general low quality. These so-called
"hybrids" quickly suffered from a bad image and in public the term
"hybrid" was more or less synonymous for poor quality. Consequently
the production of quality wine from these "hybrids" was forbidden by
law in the twenties of the last century (being still valid within the European
Community). This was an immense drawback causing the termination of grapevine
breeding in most countries. Fortunately, for example in Germany, the situation
was quite different. Since about 1926 resistance breeding was and still is
supported by the government creating an environment for very successful
grapevine breeding programs:
During
the eighties the first new bred varieties were placed in official suitability
tests in Germany. In 1992, the white variety Phoenix was the first variety
derived from resistance breeding which became registered as a protected
variety. Further cultivars followed and till the end of April 2004 twenty new
varieties obtained plant variety protection, twelve of them are registered in
the German National Variety List and depending from the individual state with
viticultural areas up to twelve are also
classified, meaning they are permitted to be planted in one or more vine
growing regions of Germany. Currently, the red variety Regent is the most
successful one (see Figure 4 for history of this variety). Regent belongs
presently to the top five most planted cultivars in Germany. Since its first
classification in 1996 its growing area rapidly increased to 1350 ha in 2003.
The evaluation
of Regent (Table 2) revealed that yield and quality parameters like sugar and
acid content fit very well with some of the most important other red varieties
in Germany. The tendency of lower yield and higher sugar content meets vine
growers' demand. The degree of mildew resistance against powdery and downy
mildew (Figures 5 and 6) as well as the
resistance against botrytis is high, however, Regent is not immune. The
experience under practical viticultural conditions during the last years
confirms that on average plant protection measures for the mildews can be
reduced by about 80% or even more. The genealogy of Regent, as depicted in Fig.
4, is rather complex and can be traced back to several Vitis species as sources
for multiple resistance.
In
addition to mildew and botrytis resistances Regent provides further advantages
for German viticulture: e.g. its high winter frost tolerance, the early grape
maturity and the potential to produce deeply coloured wines. Compared to the
traditional German red vine varieties like Pinot noir or Blauer Portugieser the
content of anthocyanins is considerably higher which is because of their
antioxidative effect positive in respect of nutrition physiology. Wines are
full bodied with a nice balance of tannins and flavour and they often remind on
wines originated from southern grape growing countries. Wine tastings in recent
years by numerous experts confirmed that Regent wines are of superior quality.
Moreover, Regent gets more and more accepted by consumers.
In
summary, efforts in resistance breeding proofed to be successful and new
varieties provide the opportunity to reduce considerably plant protection
measures while maintaining traditional quality standards. This is beneficial
from an economical and an ecological point of view and hence to vine growers
and the consumers.
What are the future perspectives for grape breeding?
Generally
the big disadvantages of the conventional breeding is the tremendous time
consumption on one side (compare Fig. 4) and the lack of knowledge about the
genetics on the other side. New biotechnological methods offer now new
perspectives. The development and the use of molecular marker-techniques look
very promising (MAS = marker assisted selection). Suitable molecular markers
offer the possibility for diagnosis of important viticultural traits like
disease resistances at an early breeding stage. They will be most suitable to
dissect the genetics of resistance in order to combine several genes to achieve
durable resistance. The mildew resistances are a good example for this
accumulation or, in terms of breeding, this pyramidisation. The correlation of
a resistance locus to distinct markers allows an effective resistance gene
management aiming at the combination of as many resistance loci as possible in
one genotype. Furthermore, molecular markers will be an important tool to
explore the genetic resources of Vitis. Loci coding for resistance can be
identified within the Vitis gene pool and by using markers can be followed for
further breeding work.
The
development of molecular markers is also a possibility to finally allow the
identification of other agronomically relevant genes. This would facilitate MAS
more widely, which results in increased efficiency in conventional breeding and
thus its acceleration. Simultaneously, access to identification and isolation
of agronomically relevant genes provides the opportunity for genetic
engineering approaches. Traits which can hardly be improved by conventional
breeding techniques are of particular value. Examples are again the resistances
against fungi, insects, bacteria, viruses etc. hence traits for which sources
of resistance are not existing or not known within the cultivars. The so-called
"non host resistance" which is based on the fact that the pathogen
cannot identify the host plant is also a medium to long term goal which might
be achieved by gene transfer. This approach promises a durable and stable
resistance.
Gene
transfer approaches, once feasible, are of particular interest to improve
varieties for deficiencies like resistance, thus maintaining the quality of a
grape. This leads to a peculiarity of wine marketing, the importance of the
varietal name for the consumer. The introduction of new varieties concomitantly
means also the introduction of new varietal names requiring considerable
efforts in the market. Only via gene transfer scenarios are imaginable where
established cultivars like chardonnay or pinto noir are improved for a single
characteristic like resistance and this modification does not lead necessarily
to a change of the varietal name and thus the product wine (compare Fig. 3).
It is
well known that genetically modified plants are a matter of public debate. But
people must be aware of the possibility that the introduction of genetically
modified grapes in the market will still last for decades (see Fig. 2). It can
be expected that in the meantime a lot of data and experience derived also from
other crops become available, which allows a more objective estimation of the
chances and risks of genetically modified vines.
Breeding and genetic engineering
Independent
of the crop species, consequent breeding efforts ultimately result in a
continuous breeding progress, e.g. annual yield increase (e.g. 2% for wheat) or
higher resistance to pathogens and pests. The continuous grapevine breeding
efforts over decades consequently resulted in improved new varieties (see Fig.
2) which are of unequivocal high quality (see Table 2), being essentially free
of off-flavours, and showing high field resistance against the mildews (see
Figs. 5 and 6). Such progress has been doubted for long.
Since
grapevine breeding requires about 25 to 30 years for the development of new
varieties (see Fig. 4), the present elite breeding strains (crossed about 15
years ago, becoming eventually a new variety in 5 years time) are superior to
new breds actually introduced into the market (crossed about 35 years ago).
Derived from crosses of varieties/genotypes showing both high resistance and
high wine quality, these elite breeding strains again will provide a
substantial progress to viticulture in about 10 years time. Thus, in the
forthcoming years conventional grapevine breeding programs will generate
varieties which show clear cut advantages and which are certainly very
interesting for ecological and economical reasons.
The
genetic modification of grapevine offers the potential to become a key
technology for the improvement of grapes in future. However, more research and
testings are required to isolate agronomical relevant genes which result in
grapevine prototypes, showing a desired phenotype. Development of gene transfer
tools (e.g. gene transfer protocols for a particular variety, procedures
avoiding antibiotic selections) is in progress and likely to be achieved within
a few years. International co-operations on grapevine genome research will
support progress substantially. Genetic maps are forthcoming, genome base
analytical tools soon become available for grapevine researchers and breeders.
However, in no case the use of biotechnological methods is an exclusive
alternative for conventional breeding. Moreover, it is anticipated to be an
additional and very effective tool for the breeder.
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[30.06.04]
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