Probably the ancient advanced civilizations of the Assyrians, Egyptians, Babylonians, Chinese, Persians, Phoenicians and other peoples were already engaged in the conscious breeding of plants and thus also grape varieties on the basis of wild vines. It was probably known for a very long time that new varieties could be obtained by sowing seeds. Presumably the Persians and later the Arabs in the early Middle Ages already deliberately bred large-berry table grapes, which were spread throughout the Mediterranean region up to Spain (Negrul's Proles orientalis). 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 beginning 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 onwards, particularly in England's greenhouses. These were 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 the Madeleine Royale and Madeleine Angevine also appeared in France, especially in the nurseries of Anger (Loire). Professional crossbreeding then began in the second third of the 19th century. A veritable boom in the breeding of new fungus-resistant hybrid varieties and phylloxera-resistant rootstocks occurred in connection with the phylloxera and powdery mildew catastrophe from the 1870s onwards, particularly in France. In terms of quantity, the breeders Georges Couderc (1850-1928) and Albert Seibel (1844-1936), as well as the Seyve-Villard vine nursery, should be mentioned. After the great success of Müller-Thurgau, large quantities of new grape varieties were created in Germany after the First World War. This led to varieties such as Bacchus, Domina, Dornfelder, Dunkelfelder, Huxelrebe, Kerner, Scheurebe, Siegerrebe and many others.
The general breeding goal in modern viticulture is to produce grape varieties with certain positive, desired characteristics and features. New grape varieties with better or, in some cases, completely new characteristics can only be produced by generative (sexual) cross-breeding: two grape varieties with desired parental characteristics are crossed with each other and from the seedlings grown, those plants are selected which best match the desired ideal variety. In maintenance breeding, existing varieties with degenerative or viral symptoms are improved by selecting the most vigorous, fertile and healthy vines. These healthy and virus-free individual vines are then propagated in masses by vegetative (asexual) means, while the degenerated, infertile vines in the vineyard are eliminated and replaced by the multiplied healthy clones of top quality (clone breeding).
Once a plant with the desired characteristics has been discovered and selected, this breeding success, which is represented by only one single plant, can be reproduced by vegetative propagation using cuttings in order to produce enough clone copies in vine nurseries for the planting of the vineyards. Due to the extremely pronounced heterozygosity (cleavage brittleness) in the species genome of the grapevine, plants propagated by sowing seeds split up again and thus no longer exhibit the selected characteristics of the mother plant. Therefore, vegetative propagation is the only way to obtain a selected variety type and multiply it unchanged (see in detail under flowering). The CPVO (Community Plant Variety Office) or national authorities established by the EU are responsible for granting plant variety protection for newly bred vine varieties or selected clones in Europe or individual countries. There are essentially four different breeding strategies, some of which are used in combination one after the other. These are cross-breeding, selection or selection, mutation and maintenance breeding.
The new breeding of new grape varieties by crossing and generative (sexual) reproduction of two parent varieties. The heterozygosity of the vine, as mentioned above, means that the progeny also have different characteristics than the parents. This basically positive phenomenon is called the heterosis effect. As a rule, the parents are different varieties, thus avoiding negative inbreeding effects. In the berries of the mother variety (this is always the first mentioned variety in the pedigree) the seeds intended for sowing ripen. The father variety provides the pollen for fertilization of the eggs and spermatozoa (special DNA analyses can also be used to determine the direction of crossing). The aim is to select from the progeny those plants which best express the desired characteristics or ideally combine the special advantages of the two parent varieties. Common breeding objectives include higher must weight, late budding, earlier ripening, looseness, higher resistance to climatic conditions such as frost, drought and water stress, and resistance to various fungal diseases such as botrytis and both types of mildew.
If the crossing is made with two grape varieties of the same species such as the European Vitis vinifera, for example, it is called an intraspecific (intra-species) crossing. However, if two different species are involved, for example Vitis vinifera with Vitis labrusca, this is called an interspecific cross. In this case the result of the crossing 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 (n = 19). Crossing Vitis rotundifolia (n = 20), which belongs to the subgenus Muscadinia, with species of the subgenus Vitis (n = 19) is difficult because of the incompatible chromosome sets (2n = 38 +1) and is only possible if the latter are used as the mother. But even then, sterile, malformed specimens without fruit attachment are often found among such offspring, which makes breeding lines with Muscadinia genetic material difficult or even impossible.
In the case of crossbreeding, castration of the hermaphroditic individual flowers of the vine intended as mother must be carried out shortly before the beginning of flowering. From one or more of its blooms, all (not yet shed) flower sheaths are removed with tweezers and the anthers with the pollen sacs and the pollen grains (male gametes) contained therein are plucked off by hand. This leaves only the bare ovaries with the female scars. Then, the treated gametes are covered with bags in order to exclude spontaneous self- or cross-fertilisation by early pollen flight. When flowering has begun, the previously harvested pollen of the father variety is trickled into the bags. Then the bag is shaken so that the pollen grains flying around can stick to the scar. The bags remain over the pollen until fruit formation begins. The seeds of the developing berries are subjected to a stratification phase (cold treatment) lasting several weeks and then germinated on a germination bed. Since never all seeds germinate, several hundred seeds are always placed in the soil.
The 200 to 400 seedlings from the first generation of crossbreeding used are known technically as F1, which means 1st branch or daughter generation. These usually 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. In order to improve the characteristics, backcrossing (backbreeding) is often carried out with a parent selected for very good wine quality. By crossing and selecting several times in the F2 or F3 generation, undesirable or negative traits can ultimately be eliminated (displacement crossing) or new positive traits can be selected, existing ones retained or enhanced in their expression. The latter is called transgression, when the performance of the parent varieties (e.g. early maturity, nutmeg flavour) is even exceeded by the daughter varieties. The opposite is regression, i.e. the regression of positive traits. In addition to crossbreeding and sowing, selection among the seedlings must therefore also take place continuously.
For the new breeding of modern fungus-resistant varieties, interspecific crosses (species of the 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, in these interspecific crosses, the undesirable Foxton of the American vines is also very easily inherited, which is already palatable in the lowest concentrations. Therefore, repeated back-crossings and cross-pollinations have to be made in order to approach European quality standards again while maintaining the highest possible fungal resistance. For approval reasons, the end product should no longer exhibit typical hybrid characteristics. These are continuous tendrils, a closed shoot tip or a higher content of the dye malvidin diglucoside. Ideally, one should try to breed Vitis vinifera varieties with a crossed resistance gene complex, whereby the fungal resistance weakens more and more with each back-crossing 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 final result - the new variety - is far from being suitable for cultivation in practice. Instead, a very complex and laborious evaluation process, lasting decades, follows until the new variety can be approved. The vines are tested for decades at several locations and their characteristics are constantly monitored until they are certified after passing and passing the test and thus receive the plant variety protection. After the cultivation tests have been carried out in the countries and regions, the regional or national classification and approval 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 long tests and quite a few have to be withdrawn.
This oldest breeding method has been used by humans for thousands of years. In the process, conspicuous vine plants with interesting characteristics were cultivated and propagated vegetatively using cuttings. In present-day Georgia, grape seeds from cultivated vines have been found dating from between 5,000 and 7,000 BC. Probably no specific pollination was carried out yet, but the sowing of grape seeds may have been an early and widespread method of selecting grape varieties with new characteristics from the germinated seedlings. Certainly, seedlings have always germinated spontaneously. Grape varieties with hermaphroditic flowers were preferred, as these did not have to be pollinated by other plants and ensured a reliable yield. A distinction is made between mass selection and clone selection.
In mass selection (also known as field selection massale), certain vines with desired positive characteristics such as ripeness, grape shape (e.g. loose berry) or resistance (e.g. frost, drought) are selected in a vineyard for the purpose of reproduction. This can also be several (many) vines in this vineyard. From the selected vines, brushwood is cut and grafted onto suitable rootstocks. This is then used to replace dead, diseased or for other reasons removed vines in the vineyard. In this way, a vineyard can be renewed little by little.
In contrast, clone breeding involves selecting a single vine (mother vine), which is then vegetatively propagated in a nursery and used in many vineyards. This form is used when a completely new vineyard is to be created and is widely used today. The vines in a vineyard are then, so to speak, all 100% genetically dentistry - clones. 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 one 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 plant parts of the vine capable of regeneration. It is often isolated plant tissues that are subjected to special treatment in the laboratory. Afterwards, new plants are regenerated from the tissues, which are evaluated for their altered properties. Treatment with colchicine (a toxic ingredient from seeds of autumn timeless plants) can, for example, produce plants with tetrapolidene (4n = 76) chromosome sets that are more productive but also more susceptible to environmental stress. However, these methods usually involve manipulative genetic engineering and are still very controversial.
In the vineyard, morphologically modified shoots may grow out in buds or cell lines as a result of spontaneous and accidental mutations, from which new grape variety clones can be branched off again by vegetative propagation. Particularly well-known for this are, for example, the variety complexes of very old varieties such as Pinot, Traminer, Chasseals or Muscatel. These have produced numerous mutation-related variants and somatic chimeras that can be distinguished visually or by taste and, with more effort, usually by genotype (clone variants). By clone selection, such naturally occurring mutants are visually selected and obtained and multiplied by vegetative propagation as a "fake" variety with its own name or as a new clone. In this case natural processes of nature are used.
In addition to new breeding and selection of new grape varieties from seedlings or the selection of visually striking clone mutants, less spectacular conservation breeding plays an important role in practice. Each vine has its own specific life history, in which it has been subjected to climatic capers, the attacks of numerous vine enemies, as well as numerous mechanical interventions. A variety-specific aging process also takes place, which leads to a reduction of the vine's defences and promotes infections with viruses, bacteria or fungi. All this leads to a slow but steady decline in performance (degeneration), the decomposition of root mycorrhiza (plant-fungus symbiosis) and increasing vine fatigue.
The production and growth of the old vines in many of the 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 vines that were growing, healthy and productive, as well as vines that were also resistant to blossoming and did not tend to trickle. First there were Silvaner vines, later other varieties such as Riesling andPinot Noir followed. The "best" vines in the vineyards were selected according to visual criteria, marked and propagated by cutting. These primary clones were planted in special facilities for further observation under uniform growing conditions.
Over time, this has led to the development of the standardized procedure of single stock selection. The quality of the primary clones in the experimental vineyard is recorded and evaluated over a period of five years. A single stock that has received the best evaluation (5 points) five times is then called "elite stock" and propagated further. Today, such a stock must also meet the criterion of virus freedom, for which purpose standardised ELISA tests are available for testing for grape-specific virus types. Ten grafted vines are produced from this elite stock by grafting, which are again observed and tested for five years (intermediate test). If this test was positive in all aspects (yield stability, flowering stability, yield level, wine quality etc.), the main test is carried out with at least 100 vines. This extends over five years with statistical evaluation. If these selected vines have received a positive evaluation in all disciplines, this selected material is called a clone and receives an approval number.
These yield clones, which are positively selected according to health and yield criteria, usually do not differ from each other in their morphological characteristics, but mainly in characteristics that can usually only be statistically determined over the years, such as a slightly different flowering strength, the number of grapes on the vine, the average grape size, or the density of the berries. Growth characteristics such as upright or lateral growth, the time of budding, the duration of the ripening period, the time of vegetation completion, wood ripeness 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 in the case of a new variety, the clones tested must be approved by official bodies. With the approval, the breeder undertakes to provide breeding care for the clone until it is deregistered and to guarantee the maintenance of clone health and specific clonal characteristics. Only then are new clones added to the list of varieties with certified clone material. Now they may be vegetatively propagated in commercial nurseries, where they are purchased by the winegrower and planted in the vineyards. In order to preserve the good qualities of these plants, constant observation, virus and nematode control and, if necessary, positive selection in the clone mother gardens must be carried out.
Ursula Brühl, Doris Schneider, Julius Kühn Institute (JKI)