The beginning of this section in the annual growth cycle the grapevine, is about six to eight weeks after that expulsion, The exact time of the year-specific temperature development that reached temperature sums depending on the location and the variety-specific growth under changing weather conditions. Constant warm temperatures with good water supply speed up the speed of shoot growth and thus the formation of the inflorescence (Latin inflorescence, depending on the country and region, also flowering, umbel, dotzen or Geschein) on the third to seventh drive node, Depending on zonalem climate, Microclimate and solar radiation, flowering takes place in the northern hemisphere from mid-May to late July (in Central Europe, the beginning according to old winegrowers rule on the 24th June = St. John's Day, plus or minus eight days), in the southern hemisphere from November to mid-December. In contrast to many other flowering plants, the single flowers of the vine are small, greenish-yellow and rather inconspicuous because of the absence of petals and flowers. From the single flowers form with the fruit ripeness the individual berries of the grape,
In the pre-bloom stage, the longitudinal axis of the inflorescence first stretches, then the lateral branches spread with the still close-packed, closed single flowers. With increasing development, the single flowers dissolve from the flower bandage, swell and turn to the green-yellowish shortly before the actual beginning of flowering. The beginning of the flowering is set when, in dry, warm weather, the first perianth (perianthium), which has grown over to a flower cap, comes loose from the flower bottom. At lower humidity the flower toads are dropped by means of a sophisticated jumping mechanism, so that the honey-scented scars are exposed and the stamens can spread.
The single flowers of the cultivated vine are with most Rebsorten hermaphroditic or two-sexed. That is, they contain in a single flower both the stamen with the male gametes in the pollen grains (= pollen) and the ovary with the female oocytes and the scar to be pollinated (see also in detail in detail below flower bud ). The full flowering stage is reached when about half of the flower toads have been dropped. However, the individual flowers never bloom at the same time, but in a time-delayed sequence, as well as the individual batches of the vine depending on exposition (Sunlight) and position on the fruit shoot not simultaneously, but start with a time delay with the flower.
The total flowering time is normally about eight days, but it can also last up to three weeks in bad, wet-cold weather. With increasing global warming or the climate Change A trend can be observed for earlier flowering dates with shorter flowering time. The number and size of the bouquets as well as the number of single flowers were already created a year earlier in the formation of the winter bud (see initiation ). On a fruit shoot are usually one to three (to a maximum of five) inflorescences in the form of a so-called panicle (actually, the term grape is not correct for the inflorescence of the vine). After flowering, pollination and successful fertilization, the ovary develops into a berry and the fruit into a grape. each grape has an average of about 150 berries. However, it depends on the fertility success, if from the maternal tissue of the Fruchtknotens actually berries a berry. In bad weather, the process of pollination and the unfertilierten flowers suffers Verrieseln (fall off).
There are also varieties with functional though female Flowers in which the stamens have been reduced or are barren. That is often the case table grapes the case. But these are inevitably one pollination instructed why you earnings varies greatly depending on the flowering conditions and fertilization success. For seedless varieties like korinthiaki or Sultana the female reproductive organs are infertile. Without the seed growth stimulating the fruit growth, the berries remain small and atrophied, but they are suitable for the production of seedless Dry berries. Size growth of these seedless berries can be artificially induced by growth hormones ( gibberellins ).
On the other hand are the Wild vines (Vitis vinifera sylvestris) usually dioecious, that is, each vine carries either only male or only female sexual organs. In the vine, both organs are present as an attachment, but only one organ is functional, while the other is hormonally suppressed. In dioecious plants is selfing (Self-fertilization) is not possible and the fertilization of the female plants can only be done by cross-pollination with pollen of a male vine. The forced recombination of paternal and maternal hereditary genetics preserves genetic diversity in a wild population and facilitates adaptation to environmental changes ( heterozygosity = Spalterbigkeit). In viticulture, this is not desirable because of the uncertain yields. However, many are considered documents used varieties hybrids of wild vines and thus dioecious. In the breeding From records are preferred varieties with male flowers, which cause less effort because of the lack of grapes.
A selfing (Self-fertilization) is usually avoided by nature, since only the pollination secures the continuance. In hermaphrodite flowers, the female scars are self-sterile by chemical, physiological and mechanical mechanisms for their own male pollen. But there are other mechanisms in nature as mentioned. Because with the Wild vines Self-fertilization is simply prevented by the presence of the two-sexes or separate sexes. In crops, these self-sterility mechanisms have often been completely or partially bred. In the fruit and seed formation grape scaffold, berry skin and berry meat, and the seed shells are formed with the supply tissue for the embryo of the mother vine. Only the embryo in the grape seed is the result of sexual fertilization, the grape is unaffected. Riesling remains Riesling, even when fertilized by Silvaner pollen.
All vines species with the same DNA structure are crossable with each other. These are all European (Vitis vinifera), but also most American and Asian varieties. This means that most varieties can not only fertilize each other (which a priori does not yet mean reproduction), but are also crossable with each other, creating new varieties. If the seeds germinate, then the resulting seedlings spontaneous crossbred two parent plants. A variety with different from the mother places new properties is most likely to arise when a pollination made by another variety. In this way, in thousands of years countless grape varieties have spontaneously evolved naturally (see four examples in the picture). However, the genetic material of the parent plant and the parent plant are also recombined if the fertilization took place within two vines of the same variety. Their genetic differences are low, because the vines mostly in the vineyard Clones by vegetative propagation are.
The cultivated vine is for the most part self-pollinating, primarily within the hermaphrodite (autogamous) or between two flowers of the same bark, which is understood as self-fertilization in the narrower sense. Self-fertilization in a broader sense also applies between two flowers of the same vine (geitonogam). Dwarf plants of a grape variety can be pollinated not only with the pollen grains of plants of the same variety, but also of other varieties and thereby successfully cross-pollinated (xenogam), without the development of flowering to a berry is affected. However, the germinability of self-fertilized seeds (grape seeds) may be impaired. As a rule, cross-pollinated varieties are more fertile and more vital than those from self-pollination. But this is irrelevant, because in viticulture the grapes are indeed destined for pressing and their seeds not for sowing. For berry training enough pollen.
The wind is also involved in the pollen transmission to a certain extent, the seeds can fly several hundred meters. Likewise, the insects attracted by the flower scent transfer such as bees the pollen grains from one blossom to the other. In principle, however, the cultivated vine does not have to be cross-pollinated and, unlike many other plants and dioecious wild vines, it does not depend on the presence of fertilizing insects. This is a great advantage and crucial for the profitability. No matter from where the pollen grains from the stamens reach the sticky scar, they stick there (pollination), germinate and form a pollen tube, which grows into the scar and the stylus to the (only) egg in the ovary to fertilize (fertilization). From this fertilized egg cell (zygote) arise later by the so-called meiosis (reduction division and recombination division) to five (rarely six) genetically different seed pits in the berry. The genetic difference of the nuclei results from a new compilation of parental chromosomes.
In the case of grape vines grown out of grape pits without human intervention, the paternal pollen donor is not known a priori. Such spontaneously produced varieties, in contrast to the conscious new breed by man with " openly bloomed "(" Open pollinated ", abbr." OP "). Fertilization ultimately produces a single berry from every single flower. This means that a bunch of grapes with, for example, 150 berries could (theoretically) have 150 different fathers (the father being a foreign vine). Each berry of this grape would have the same mother in this case, but the grape 150 different fathers (pollen donors). The pollen may come from its own flower, from a flower of the same crop, from a flower of another crop of the same vine, from a neighboring vine of the same variety, or from vines of other varieties from neighboring vineyards.
The maternal tissue of the ovary subsequently grows to the berry with the five to six nuclei. These could grow out as mentioned above seedlings provide different varieties. From crosses between Cabernet Sauvignon x Bronner are 1983 in Freiburg three quite different grape varieties arose ( baron. Cabernet Carbon. Souvignier Gris ). The three underlying kernels could theoretically all come from the same berry. Reigns during the vine flower bad weather such as cold, rain, wind or hail before, the fertilization process is impaired. Rain, wind and high humidity hinder pollen dispersal and flight, but also cause that the jump mechanism of the coping does not work or only partially and these are not blown off, but remain loose on the scars and stick there. As a result, pollination can no longer take place. Coldness impedes the outgrowth of the pollen tubes. Therefore, never all ovules are fully fertilized.
However, since the embryo in the seed stimulates fruiting, the insufficiently fertilized berries remain smaller. The result is parthenocarpy (or Stenospermokarpie = apparent mossiness) or early Verrieseln (Dropping) of completely unfertilized flowers. The grape has less then and petits Grapes on. However, this does not have to be a disadvantage because a reduced yield can increase the quality. Because the produced ingredients of the grapevine are now concentrated on a smaller number of berries, and that may result in more extractives, higher sugar content and overall better wine quality. Just a few weeks after flowering, the berries reach pea size. This is already part of the next development step, the fruit set,
Regarding fertilization process see also under flower bud and hermaphrodite flower, A list of grapevine relevant keywords is under grapevine contain. All aids, works and measures in the vineyard during the growth cycle can be found under the keyword Weingarten Care,
Graphics: Taken from Bauer / Regner / Schildberger, viticulture,
ISBN: 978-3-70402284-4, Cadmos Verlag GmbH