FLOWERING AND POLLINATION GRAPE VINE STAGES
In the vine´s life cycle the process following bud break, coinciding with pollination and proceeding fertilization, which eventually leads to fruit set. Vine flowers are small and unattractive, pale green in color, the vast majority having both female (a pistil, containing ovary, style and stigma) and male (stamens) organs.
After pollinitation, the fertilized ovaries form seeds, whilst the flower leaves enlarge forming the pulp and the skins of the grapes. Likewise the inflorescences are transformed into bunches. Flowering, which entirely depends upon pollen generation, is seriously affected by changes in weather (especially cold and wet conditions) which may have a negative impact on the vineyard´s yield.
The pollination is the process which occurs during flowering and consists of the transfer of pollen from the anthers to the stigma in the vine´s flowers, where it germinates and fertilizes the ovules, subsequently giving rise to fruit set. If it is done between flowers of the same plant, it is called self-pollination, and when occurring between flowers of distinct plants, cross-pollination.
In nature the self-pollination, is by far the most common and transfer is produced with the aid of vectors such as wind, rain, water, insects or birds. Pollination is followed, some two or three days after, by fertilization which will be on its turn dependent on the rising of temperature.
The fruit set or fructification is a very important temporal process by which the vine´s flowers are transformed into grapes. It occurs right after flowering as a result of adequate pollination, which means that only correctly fertilized flowers can become fruits and develop seeds. As nature determines, neither all flowers are transformed into fruits, or are all fruits formed with seeds. This naturally occurring percentage of failures can be aggravated, thus affecting wine quality, by vine growth disorders such as coulure and millerandage.
- Coulure or shatter (Corrimiento): Poor fruit set in the vine that leads to unripe grapes falling off prematurely. To a certain extent it is a natural phenomenon, for vines cannot bear and mature all possible grapes. It is not natural when the losses are too high. It is then provoked by a serious deficiency in the formation and accumulation of sugars in the plant. The causes of it are manifold, though clearly correlated with cool weather, excess soil fertility, incorrect pruning and varieties employed. It should not be confused with millerandage.
- Millerandage (Milerandaje): Abnormal growth of grapes within the bunches, which contain berries of significant variability in size as in ripening levels. Some grapes have fewer seeds than normal or are even seedless. Cold or bad weather during flowering, infection by fan leaf degeneration or a boron deficiency may be behind it. Millerandage affects yield but not necessarily quality. It is similar though not exactly the same as coloure.
THE BIOLOGICAL CYCLE OF THE GRAPE VINE
- Bleeding: The biological cycle begins with bleeding, the process by which the vine stock awakes. Bleeding can begin very early (end of January) in temperature and tropical zones as Lanzarote in the Canary Islands, and can be delayed until the (end of March) in cold and high areas with dry and severe climates on the Spanish central plateau, like Calatayud.
In Spain, it usually occurs towards the (end of February) or the (beginning of March). As temperatures become milder (10°C) in early spring and this is the first external sign of activity after winter rest. The underground part of the vine begins its activity, pumping sap to the above ground part. Since the aerial part is still dormant, the sap bleeds out of the wounds left by pruning. This lasts a few days.
- Budbreak: The bleeding is followed by budbreak, in which buds open and new growths emerge. In (April or May,) leaves are formed and the foliage which carry out vital functions in the plant as are transpiration and photosynthesis, by which inorganic energy is transformed into organic. When bud burst or budding takes place and buds swell as a result of their cellular development.
- Growth and Development of green shoots: After bud burst, the vine develops miniature organs that go through various stages and eventually become shoots, leaves or tendrils, depending on their location on the trunk.
- Flowering: Flowering takes place in late spring or early summer (May or June), when average temperatures rise above 15°C. Setting takes place in those flowers that are fertilized and turn into berries. This effectiveness and precise occurrence will mark the ripening period of the fruit and the yield of the harvest.
- Fruit formation: Following fertilization, (in Jun or July), fruit set or formation of the grapes in bunches takes place. After verasion, the process by which grapes change color during the course of the summer, the berries undergo a slow and important evolution until they reach their optimal pint of ripeness, when they will be harvested.
- Ripening: The berries begin to develop after setting. The berry begins to ripen when veraison occurs. This is the time when the hard, green berry turns translucent in the case of white grapes or begins to turn to colour in the case of red grapes.
- Harvest: This crucial time extends normally (from August to the end October), and will depend basically on the type or style of wine sought, the environmental conditions like climate, diseases, etc., the variety employed and the techniques and systems chosen for cultivation. The majority of vines yielding grapes adequate for vinification belong the species of Vitis vinifera, grafted onto rootstocks from American hybrids.
- Dormancy: When temperatures drop below 12°C, the vine goes into winter dormancy. The low temperatures prevent practically all plant activity. Dormancy or sleep is the normal state of vines in winter. This period normally starts with autumn or leaf fall, although buds are in a state of so called organic dormancy ends with budbreak in the spring. Pruning is carried out when the vines are dormant, and buds and cuttings taken from the vines at this time are used in propagation. The vines are literally asleep or dormant, with minimal metabolic activity.
