There are three ways in which the sexual organs are arranged in plants. In the first possibility, the "sexual organs" are separate on two different plants, for example, a tree with only functional male parts (and stunted female parts), and a second tree with only functional female parts (and stunted male parts). Now the two must "come together". The plants are dependent on outside help, i.e. wind and insects. Many flowers are therefore not fertilized and the fruit yield can be relatively low. By the way, such plants are called "dioecious", because the male and the female sexual organs are each on their own "house" (plant). As already mentioned above, this form is usually found in most wild vines.
The second possibility are plants where the genitals are separate but present on the same plant. This means that there is a male part on branch A and a female part on branch B. There, it is easier to come together, but still difficult, because the plant is also dependent on external help. Such plants are called "monoecious" because both sexual organs are located on one "house". The third possibility are hermaphrodites, where the male part (seed = pollen) and the female part (stigma) are united in one organ. This is usually the case with the cultivated vine. Here the plant is not or hardly dependent on external help. At the time of flowering the male pollen sack opens, the pollen is released and collected by the sticky female stigma underneath. However, the plant must not be self-sterile, which is often the case with non-cultivated plants. In this way it protects itself, so to speak, from (mostly negative) inbreeding; only cross-pollination leads to positive heterosis effects.
If fertilization by pollen from the same vine occurs during flowering on one (autogamy) or between two flowers (geitonogamy), this is called self-pollination or self-introduction. If two different vines are involved (whether the same or different varieties), this is called cross-pollination (xenogamy). It is largely irrelevant for fruit set and berry development whether the seed itself has been self-pollinated or cross-pollinated. However, the cultivated vines are usually not self-sterile. For the most part, self-pollination takes place within the hermaphrodite blossom. However, the problem-free self-pollination is somewhat different for each variety. Amongst others, Grünling (Adelfränkisch) and some Traminer clones lack the ability to do so. Such varieties are often parthenocarpic (virgin) and thus seedless (without seeds). They need pollen dispensers, which used to stand all around in old vineyards in a mixed set. In single-variety plants they cause problems, especially in bad flowering weather, when the pollen does not fly far enough and is washed out of the air by rain. A self-pollinator that is also good in wet weather is, for example, the Welschriesling.
It is only through fertilization that a single berry develops from each individual flower. If there is no fertilization, then there is no berry, with such flowers it comes to trickling. In a fertilized berry the up to five (rarely six) embryos = seeds are potentially ready for a new variety. This means that all genes of the two parents have been passed on there. If it was a self-fertilization, then this is for example Grüner Veltliner x Grüner Veltliner. But if the pollen came from the neighboring garden where a Pinot Noir is located, then this is Grüner Veltliner x Pinot Noir (the mother is always named first). This natural crossbreeding result is, however, as already mentioned, only potentially (dormant) present and is not used in viticulture. The grapes always correspond 100% to the mother in terms of appearance and varietal characteristics, regardless of the paternal genes in the grape seeds.
Only then, when such a grape seed of a grape reaches the ground, begins to germinate there, grows into a seedling (young vine), then it comes to flowering, a fertilization takes place and finally grapes are formed, only then is this grape seed the now realized result of a possibility that until then was only potentially available. A new grape variety with possibly new characteristics is created when fertilisation by a foreign vine of another grape variety has taken place. In this way, the current 8,000 to 10,000 grape varieties have been formed over many thousands of years by spontaneous or natural crossbreeding. In principle, the genes are remixed even when two vines of the same variety are involved, but the genetic differences are then minimal.
In a new breed, nature is imitated, so to speak. One castrates the mother variety by removing the male flower part to prevent self-pollination. Then one takes pollen from the desired father variety and places it on the mother's stigma. From the fully grown berry the seeds are removed, placed in the ground and a new vine is planted. This is done with a few hundred berries and, depending on the desired characteristics, selects more and more until the best or most appropriate results are obtained. A complete list of keywords relevant to grape varieties can be found under vine.
Graphic: Taken from Bauer/Regner/Schildberger, Viticulture,
ISBN: 978-3-70402284-4 Cadmos publishing house GmbH