The ancient civilisations of the Assyrians, Egyptians, Babylonians, Chinese, Persians and Phoenicians were probably already involved in the deliberate cultivation of plants and therefore also grape varieties based on wild vines. The fact that new varieties could be obtained by sowing seeds had probably been known for a very long time. The Persians and later the Arabs in the early Middle Ages probably already deliberately bred large-berried table grapes, which spread throughout the Mediterranean region as far as Spain. Modern breeding as a deliberate, manually induced crossing of two parent varieties with the targeted use of paternal pollen probably only began in Christian Europe with the start of botanical systematics, for which Carl von Linné (1707-1778) and Charles Darwin (1809-1882) laid the scientific foundations.
New grape varieties through targeted breeding activities such as seed sowing or crossbreeding were created from the first third of the 19th century, particularly in the greenhouses of England. These included, for example, the table grape varieties Foster's White Seedling and Lady Downe's Seedling. In the middle of the 19th century, many new varieties such as Madeleine Royale and Madeleine Angevine were also created in France, particularly in the nurseries of Anger (Loire).
Professional cross-breeding began in the second third of the 19th century. A real boom in new varieties of fungus-resistant hybrids and phylloxera-resistant rootstocks occurred in connection with the phylloxera and mildew catastrophe from the 1870s, particularly in France, with the breeders Georges Couderc (1850-1928) and Albert Seibel (1844-1936), as well as the Seyve-Villard vineyard, being particularly noteworthy in terms of quantity. Following the great success of Müller-Thurgau, large quantities of new grape varieties were also created in Germany after the First World War. This led to varieties such as Bacchus, Domina, Dornfelder, Dunkelfelder, Huxelrebe, Kerner, Scheurebe, Siegerrebe and many more.
The general breeding objective in modern viticulture is to produce grape varieties with certain positive, desirable characteristics and traits. New grape varieties with better or, in some cases, completely new characteristics can only be produced by generative (sexual) breeding: two grape varieties with desirable parental characteristics are crossed with each other and the plants that best correspond to the desired ideal variety are selected from the adult seedlings. In maintenance breeding, existing stocks of varieties with degenerative or viral symptoms are improved by selecting the most vigorous, most fertile and healthiest vines. These healthy and virus-free individual vines are then propagated en masse by vegetative (asexual) means, while the degenerated, unfertile vines in the vineyard are eliminated and replaced by the multiplied healthy clones of top quality(clonal breeding).
Once a plant with the desired characteristics has been discovered and selected, this breeding success represented by a single plant can be reproduced by vegetative propagation via cuttings in order to produce enough clone copies in vine nurseries to stock the vineyards. Due to the extremely pronounced heterozygosity in the genome of the grapevine species, plants propagated by sowing seeds split again and therefore no longer have the selected characteristics of the mother plant. For this reason, vegetative propagation is the only way to preserve a selected variety type and to multiply it unchanged (see details under Flowering).
The Community Plant Variety Office ( CPVO ) established by the EU or the national authorities are responsible for granting variety protection for newly bred grape varieties or selected clones in Europe or the individual countries. There are essentially four different breeding strategies, some of which are used in combination. These are cross breeding, selection breeding, mutation breeding and maintenance breeding.
This refers to the breeding of new grape varieties by crossing at least two and sometimes several parent varieties by crossing a cross product again (possibly several times). In any case, this is generative (sexual) propagation. The above-mentioned heterozygosity of the vine means that the offspring also have different characteristics from the parents. This basically positive phenomenon is called the heterosis effect. As a rule, the parents are different varieties, which avoids negative inbreeding effects. The seeds intended for sowing ripen in the berries of the mother variety (this is always the first named variety).
The father variety provides the pollen for fertilising the ovules and seeds (special DNA analyses can also be used to determine the direction of crossing ). The aim is to select plants from the offspring that best express the desired characteristics or ideally combine the particular advantages of the two parent varieties. Common breeding goals are higher must weight, later budding, earlier ripening, loose berries, compatibility with certain soil types, higher resistance to climatic conditions such as frost, drought and water stress, as well as resistance to various fungal diseases such as botrytis, powdery and downy mildew.
If the cross is made with two grape varieties of the same species, such as the European Vitis vinifera, it is referred to as an intraspecific (intraspecific) cross. However, if the cross involves two different species, for example Vitis vinifera with Vitis labrusca, it is referred to as an interspecific cross. In this case, the result of the cross is called a hybrid. All species of the subgenus Vitis can be crossed with each other and the offspring are capable of reproduction due to the same DNA structure (2 x 19 =38). Crossing Vitis rotundifolia (2 x 20 = 40), which belongs to the subgenus Muscadinia, with species of the subgenus Vitis is difficult due to the incompatible chromosome sets and is only possible if the latter is used as the mother. But even then, sterile, malformed specimens without fruit set are often found among such offspring, making breeding lines with Muscadinia genetic material difficult or even impossible.
During the crossing process, the hermaphrodite single flowers of the vine designated as the mother must be castrated shortly before flowering begins. All (not yet shed) perianths are removed from one or more of its shoots with tweezers and the anthers with the pollen sacs and the pollen grains they contain (male gametes) are plucked off by hand. This leaves only the bare ovaries with the female stigmas. The treated clusters are then covered with bags to prevent spontaneous self-fertilisation or cross-fertilisation due to early pollen dispersal. When flowering has begun, the previously harvested pollen of the father variety is sprinkled into the bags. The bag is then shaken so that the pollen grains flying around can stick to the stigma. The bags remain over the stigma until the beginning of fruiting.
The seeds of the resulting berries are subjected to a stratification phase (cold treatment) lasting several weeks and then germinated on a germination bed. As never all the seeds germinate, several hundred seeds are always placed in the soil. The 200 to 400 seedlings grown from the first generation of crosses are technically referred to as F1, which means 1st filial or daughter generation. As a rule, these do not yet show the desired characteristics to a satisfactory degree, so that some of the promising candidates are selected from this F1 seedling population in order to carry out further crosses. To improve the characteristics, backcrossing (backbreeding) is carried out with a parent selected for very good wine quality.
Repeated crossing and selection in the F2 or F3 generation can ultimately eliminate undesirable or negative characteristics (suppression crossing) or select new positive characteristics, maintain existing ones or enhance their expression. The latter is called transgression when the performance of the parent varieties (e.g. earliness, nutmeg flavour, yield) is surpassed by the daughter varieties. The opposite of this is regression, i.e. the regression of positive characteristics. In addition to crossing and sowing, the seedlings must therefore also be constantly selected. As a rule, several thousand crossbred grapevine plants are needed to find all the positive characteristics for use as a later grape variety at a high level, which is then propagated.
For the new breeding of modern PIWI varieties (fungus-resistant), interspecific crosses (species of European Vitis vinifera with American or Asian species) are carried out in order to cross the mildew resistance of American vines, which is not present in European vines, into Vitis vinifera varieties while maintaining the high wine quality. Unfortunately, with these interspecific crosses, the undesirable foxy of the American vines is also very easily passed on, which can be tasted even in the smallest concentrations. For this reason, repeated backcrossing and intercrossing must be carried out in order to get closer to European quality standards while maintaining the highest possible fungal resistance.
For authorisation reasons, the end product should no longer have any typical hybrid characteristics. These are continuous tendrils, a closed shoot tip or a higher content of the colouring agent malvidin diglucoside. Ideally, Vitis vinifera varieties should be bred with a cross-bred resistance gene complex, whereby the resistance to fungi weakens more and more with each backcross with Vitis vinifera varieties.
The parentage of the newly created and selected variety seedling at the end of the crossing process is represented by a breeding scheme (pedigree) in order to be able to trace the complicated and interwoven crossing steps. However, the end result - the new variety - is far from being suitable for cultivation in practice; instead, a decades-long, very complex and painstaking evaluation process follows before the new grape variety can be authorised. The vines are tested for decades at several locations and their characteristics are continuously monitored until they are certified after passing the test and thus receive variety protection. After successful cultivation tests in the countries and regions, the regional or national classification and authorisation for commercial cultivation takes place, which is initially limited to certain wine-growing regions and can last for many years. Not all varieties pass these tough, lengthy tests and quite a few have to be withdrawn.
This oldest breeding method has been used by humans for thousands of years. In this process, conspicuous grapevine plants with interesting characteristics were cultivated and propagated vegetatively via cuttings. Grape seeds from cultivated vines dating back to between 5,000 and 7,000 BC have been found in what is now Georgia. Although pollination was probably not yet carried out systematically, the sowing of grape seeds may have been a widespread method of selecting grape varieties with new characteristics from the sprouted seedlings. Seedlings have certainly always sprouted spontaneously. Grape varieties with hermaphrodite flowers were favoured as they did not have to be pollinated externally and guaranteed a reliable yield. A distinction is made between mass selection and clonal selection.
In mass selection (also known as field selection, French massale = en masse), certain vines with desired positive characteristics such as ripening time, grape shape or resistance (e.g. frost, drought) are selected in a vineyard for the purpose of reproduction. This can also be several (many) vines. From the selected vines, branches are cut and grafted onto suitable rootstocks. These are then used to replace vines in the vineyard that are dead, diseased or need to be removed for other reasons. In this way, a vineyard is gradually renewed.
In contrast, clonal breeding involves selecting a single vine (mother vine), which is then vegetatively propagated in a nursery and used in many vineyards. This method is used when a completely new vineyard is to be planted and is widely used today. The vines in a vineyard are then all 100% genetically identical - clones, so to speak. Critics of this form complain about the resulting loss of genetic diversity in such monocultures. This is taken into account by using different clones of a grape variety in one vineyard.
Artificial mutations can be deliberately induced by ionic or radioactive irradiation or biochemical treatment of cell cultures, callus tissues, seeds, pollen grains, buds and cuttings or other parts of the vine capable of regeneration. These are often isolated plant tissues that are subjected to special treatment in the laboratory. New plants are then regenerated from the tissue and evaluated for their altered properties. For example, treatment with colchicine (a toxic substance from autumn crocus seeds) can produce plants with tetrapolide (4n = 76) chromosome sets, which are more productive but also more susceptible to environmental stress. However, these methods usually involve manipulative genetic engineering and are still highly controversial.
In the vineyard, spontaneous and random mutations in buds or cell lines can result in morphologically modified shoots, from which new grape variety clones can be derived through vegetative propagation. Varietal complexes of very old varieties such as Pinot, Traminer, Chasselas or Muscat are particularly well known for this. These have produced numerous mutation-related variants and somatic chimeras, which can be distinguished visually or in terms of flavour and, with greater effort, usually also genotypically (clone variants). Through clone selection, such naturally occurring mutants are visually selected and obtained and reproduced through vegetative propagation as a "non-genuine" variety with its own name or as a new clone. In this case, natural processes of nature are utilised.
In addition to the new breeding and selection of new grape varieties from seedlings or the selection of visually striking clone mutants, less spectacular maintenance breeding plays an important role. Each vine has its own specific life story, in which it has been subjected to climatic caprices, attacks by numerous vine enemies and numerous mechanical interventions. A variety-specific ageing process also takes place, which leads to a reduction in the vine's defences and favours infections with viruses, bacteria or fungi. All this leads to a slow but steady decline in performance (degeneration), the breakdown of the root mycorrhiza (plant-fungus symbiosis) and increasing vine fatigue.
The production and vigour of the old vines in many old vineyards at the turn of the century was therefore already severely impaired. In order to improve the yields of the vineyards again, some vine experts such as Gustav Adolf Froelich (1847-1912) began to positively select vigorous, healthy and high-yielding vines that were also resistant to flowering and not prone to coulure from the end of the 19th century. At first it was Silvaner vines, later followed by other varieties such as Riesling and Pinot Noir. The "best" vines in the vineyards were selected according to visual criteria, marked and propagated by cuttings. These primary clones were then planted in special nurseries for further observation under standardised growing conditions.
Over time, the standardised procedure of single-vine selection has developed from this. The quality of the primary clones in the trial vineyard is recorded and assessed (bonitised) over a period of five years. A single vine that has received the best score (5 points) five times is then called an "elite vine" and propagated further. Today, such a stock must also fulfil the criterion of being virus-free, for which standardised ELISA tests are available to test for vine-specific virus types. From this elite stock, ten grafts are produced by grafting, which are then observed and tested for another five years (intermediate test). If this test is positive in all respects (yield security, flowering resistance, yield level, wine quality, etc.), at least 100 vines are used for the main test. This extends over five years with statistical analyses. If these selected vines have received a positive evaluation in all disciplines, this selected material is called a clone and receives an authorisation number.
These yield clones, which are positively selected according to health and yield criteria, usually differ little in terms of their morphological characteristics, but mainly in terms of characteristics that can usually only be recorded statistically over the years, such as different flowering firmness, number of grapes on the vine, average grape size or berry density. Growth characteristics such as upright or lateral growth, the time of budding, the duration of the ripening period, the time of the end of vegetation, wood maturity and other quantitative, seasonally influenced characteristics are also taken into account. The test procedure up to clone approval takes 15 to 20 years. All clones must be tested and virus-free.
As with new breeding, the tested clones must be authorised by official bodies. With the approval, the breeder undertakes to look after the clone in terms of breeding and to guarantee the maintenance of the clone's health and specific clone characteristics. Only then are new clones included in the list of varieties with certified clone material. They may now be vegetatively propagated in commercial vine nurseries, where they are purchased by the winegrower and planted in the vineyards. In order to maintain the good characteristics of these plants, constant monitoring, virus and nematode control and, if necessary, positive selection must be carried out in the clone mother gardens.
For more information on this topic, see also flowering, chromosome, DNA, inbreeding depression, crossing, new breeding, vine systematics and grape variety identification, as well as lists of relevant keywords under vineyard area and grapevine.
Ursula Brühl, Doris Schneider, Julius Kühn Institute (JKI)
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Markus J. Eser
Weinakademiker und Herausgeber „Der Weinkalender“