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R. Eibach,  and R. Töpfer     JKI Institute for Grapevine Breeding, Geilweilerhof, Germany

The first breeding activities in grapevines started around the beginning of the nineteenth century and were mainly initiated in North America. In Europe, targeted breeding activities started later and were triggered by the introduction of the mildews and phylloxera (1845–1878). Mainly private French breeders started huge breeding programmes and tried to introduce resistance characteristics from American wild species into the gene pool of the European cultivars belonging to Vitis vinifera. Today, these cultivars are still a very valuable resource for a lot of breeding programmes carried out in various grape-growing countries around the world.

Procedures in breeding have to consider the specific characteristics of the grapevine (i.e. perennial crop, hermaphroditic, space-consuming growth) in order to establish sufficiently sized progenies with adequate genetic variation. Common methods and protocols for emasculation, pollen collection, pollen storage, pollination and seed management are described. Since grapes are propagated vegetatively, potential new cultivars are already genetically fixed in the seedling stage. Nevertheless, selection processes extend up to several decades. Selection goals are predominantly influenced by climatic factors and hence their influence on the presence or the severity of individual pests and diseases. In general it can be stated that in the first part of the breeding cycle selection is predominantly focused on resistance traits while quality traits are investigated more thoroughly towards the end of the cycle after passing through multiplication steps in order to have enough crop.

Present limitations in grapevine breeding are mainly due to crop-specific limitations, access to suitable genetic resources, socioeconomic aspects and the lack of knowledge about grapevine genetics. However, concerning the latter aspect, tremendous progress has been made in recent years. Knowledge about grapevine genetics is going to increase tremendously and it can be expected that the introduction of new tools such as marker-assisted selection will increase breeding efficiency and hence breeding progress enormously.

Targeted breeding activities started around the beginning of the nineteenth century, predominantly in North America. The colonists failed to grow the delicately flavoured Vitis vinifera vines they were accustomed to, due to severe frost damage as well as the destruction of the grapes by pests like phylloxera or by fungal diseases like powdery and downy mildew. On the other hand, the sturdy native American grapes that could be grown easily produced strong-flavoured wines that they did not like. In 1822, researchers from Harvard University recommended developing hybrids between the European vines and the indigenous grapes in order to combine the hardiness and resistance of the American grapes with the pleasant flavour of the V. vinifera grapes (Cattell and Miller, 1980). During the following decades, a lot of engaged breeders like William W. Valk, Nicholas Herbemont, Hermann Jaeger or Thomas Munson developed successful newly introduced cultivars like Ada, Herbemont, Brighton or Diamond. The plethora of cultivars developed during this period are summarized as so-called American hybrids. In Europe, resistance breeding was initiated after the introduction of phylloxera and the mildews from North America in the second part of the nineteenth century. Mainly in France, phylloxera destroyed hundreds of thousands of hectares of grapevines and catalysed a lot of private French breeders to start their own breeding programme. Breeders like Gaillard, Bertille Seyve, Seibel, Couderc, Kuhlmann, Baco, Seyve Villard, Landot and others created thousands of new cultivars with the aim of combining resistance against phylloxera and the mildews as well as producing high quality. Those and other breeders were aiming at so-called direct producers, but many of these cultivars failed. In retrospect, it can be summarized that insufficient suitability tests for other viticultural traits except the resistance characteristics caused failure in the overall performance of the new cultivars. The plants were not checked thoroughly for wine quality, and this was obviously one of the major reasons why, in the public perception, resistance was associated with poor wine quality. Even today, this position is still alive in some minds. The limited reputation of those cultivars and the discovery of the fungicidal properties of copper and sulphur in 1885 led finally to a total surrender of the private breeding activities in France. Nevertheless, the historical merit of these breeders is that they created a highly valuable genetic resource carrying, to some extent, a combination of resistance and quality. These cultivars were summarized as so-called French hybrids, and they have since being used extensively for further breeding activities during the second part of the twentieth century.

In other countries, targeted resistance breeding started later. In Germany, it was initiated by Erwin Baur in 1926. First generations of new varieties resulted in cultivars like Aris or Siegfriedrebe, while Aris was the first cultivar with extensive proof that resistance and poor wine quality are not linked. But because of other viticultural deficiencies, it could not succeed on the market. Considerable breeding activities were also established in the US but also in Eastern European countries like Hungary, the former Yugoslavia, the former Czechoslovakia, the former USSR and others. Newly released cultivars like Traminette (USA), Bianca, Kunbarat (Hungary) or Regent (Germany) are examples of these successful breeding programmes. All these cultivars can be summarized as a new generation of cultivars derived from classical breeding.

Besides resistance breeding, several countries developed breeding programmes restricted to the gene pool of V. vinifera, neglecting resistance and focusing mainly on yield and quality traits, as well as other viticultural traits. This led to a series of newly introduced cultivars, mainly in northern European grape-growing countries. The most prominent example is the cultivar Müller-Thurgau, which was crossed in 1882 from Herrmann Müller in Geisenheim, Germany. Meanwhile, these breeding activities have stopped to a great extent and have largely been replaced by resistance breeding.

While wild grapes are dioecious, most of the cultivated grapes are hermaphroditic, and fertilization occurs mainly via self-pollination (Harst et al., 2009). Therefore, emasculation of plants is required to use them as female parents. This, however, is a very laborious process, both for the technique of emasculation itself and for determining the appropriate time for emasculation. Usually emasculation is carried out using tweezers with small and tiny tops. Removing all anthers completely is as important as avoiding any injury of the stigma and pistil. Therefore, good eyes and calm hands are equally important prerequisites for those doing the emasculations. Because fertilization may already happen before ejecting the cap (Staudt, 1999), the removal of anthers must be carried out at the right time ahead of flowering. Changing weather conditions, especially changing temperature cycles in the preflowering phase, complicate a reliable forecast for the determination of the optimal point in time. The beginning of bracing the flowers from the rachis along the inflorescence is the most reliable indicator for determining the optimal time for emasculation. Flowers located in the centre and basal parts of the inflorescence tend to blossom out ahead. Therefore, removing the top and the shoulder parts of the inflorescence favours a more unique flowering of the remaining flowers, promoting an enhanced fruit set after pollination.

After emasculation, the inflorescence has to be protected against random pollination due to dispersal of arbitrary grapevine pollen by wind or insects. For this purpose, bags of glassine paper are quite appropriate. These kinds of bags proved to be suitable to prevent an exceeded increase of temperature inside the bags due to sunlight exposure.

The collection of pollen from selected male parents is most frequently carried out by enclosing the inflorescences with bags right before the beginning of blooming. During flowering, the pollen drops into the bags, and the bags, including the pollen, can be removed after flowering. In many cases, a crucial point for performing crossings is the availability of pollen from the selected male parents in due time. Several approaches might be considered to solve this challenge. One projection is the use of variation of flowering time between parents by selecting the earlier flowering parent as the male. Furthermore, since pollen is already fertile some days before blooming (Koblet and Vetsch, 1968), inflorescences of pollen donors can be harvested ahead of the blossom. Drying them gently at around 25°C in a heating cabinet and subsequently pulverizing the flowers, including the pollen sacs, allows a gain of several days for pollen access. A further approach comprises the coating of potential pollen donors with a plastic foil...