The growth habit of the grape is in many ways similar to that of other fruit crops. Yet it is sufficiently different to warrant special study to understand the application of many cultural practices.
FIGURE 3. The fruiting shoot grows from the primary bud.
Grape flowers and fruit clusters are borne only on new shoots arising from dormant buds. These buds are formed in the axils of leaves the previous season and are called compound buds. This compound bud or
eye contains a group of three separate buds.
When growth starts in the spring, the primary or central bud breaks dormancy and produces the fruiting shoot (Figure 3). On young vines, this shoot may remain entirely vegetative and produce no fruits. Grape shoots do not form terminal buds, and the tip typically dies back in the winter to the lignified or
ripened portion of the cane.
Spring frosts may occasionally kill the tender primary shoot in its early stages of growth. In this case, the secondary or tertiary buds in the eye develop shoots that may—or may not—bear fruit (Figure 4). This shoot normally is less vigorous and less productive than the primary shoot. However, this characteristic of the grape permits development of a partial crop even though the primary shoots are lost.
FIGURE 4. Frost injury to the primary shoot results in new shoot growth from a secondary or a tertiary bud.
Severe spring frosts may kill both primary and secondary buds. In such cases, fruit production is lost for that season, and the remaining shoot growth may be extremely vigorous.
Cluster initiation for next year’s crop begins during mid-summer in the developing buds, which are in the leaf axils of the current season’s shoots. By the end of the growing season, the buds are fully developed and contain leaf and cluster primordia.
The following spring as these buds begin growth, final development of the flowers occurs. By this time, shoots are 6-inches long, and clusters are clearly visible. Flowering or bloom occurs after the shoots reach 18 to 24 inches, or about four weeks after bud break.
Morphologically, the grape fruit cluster is a modified tendril. Whether a tendril or a flower cluster, development is determined by the vine’s genetic code. The number of flower clusters that may develop from a single dormant bud is determined to a great extent by vine vigor and growing conditions, especially exposure to sunlight during the previous season.
Each grape species has a definite number of flower clusters per shoot. Location of these clusters on the shoot also is specific. The location and number of fruit clusters on the shoot are factors to consider in determining the vine training and pruning system. The American grape (
Vitis labruscana) characteristically forms two to four flower clusters per shoot located at nodes 2, 3, 4, and 5 from the base of the shoot. Many species of grape, including most cultivars of
V. vinifera, form only two flower clusters per shoot.
French hybrids as a group tend to flower prolifically, have four or more clusters per shoot, and produce flowering shoots from buds at the base of shoots and latent buds in the cordon as well as
count buds in the canes.
Grapes flower later than most tree fruit and are mostly pollinated by wind. Fruit set is influenced by the weather, being greatest under sunny, warm, dry conditions.
Berry growth and development occurs in three stages. Rapid cell division and growth begin in the berries following pollination at Stage I, followed by Stage II of slow berry growth, while rapid shoot and leaf growth occurs.
Veraison—softening of the berry and development of berry color—signals Stage III, where acid levels decrease and sugars increase until the grapes are mature and harvested.
Frequently during the growing season, a short, weak shoot is produced in the axil of the leaf adjacent to the bud and is known as a
summer lateral. These lateral shoots can be important sources of photosynthetically active new leaves. However, they often do not mature well enough to survive the winter and are usually removed in dormant pruning.
After the leaves drop in the fall, the term cane is applied to the mature, dormant shoot. It is from these canes that next year’s fruiting wood is selected at pruning time and from which propagation wood is taken.
The grapevine root system has important functions of moisture and nutrient element absorption as well as anchorage of the vine and production of plant hormones. In addition, the root system serves as the primary storage organ for the carbohydrate and nitrogen reserves required for early spring growth of the vine.
The root system is concentrated in the well-aerated upper 18 to 24 inches of soil but can penetrate deep into soil if not impeded by a hard pan or a high water table. By proper selection of rootstocks, grapevines can be grown in a wide range of soil types.
Grapevines require some kind of structural support for commercial and home production. The trellis or arbor provides support so the vine can be managed efficiently. This support exposes more foliage to sunlight, which increases bearing surface and improves fruit color and quality.
Wire trellises, arbors, or other structures desired for a specific purpose or design may be used. Grapevines must be pruned annually to maintain productivity and fruit quality.
http://ohioline.osu.edu/b919/0003.html
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