Fig. 1
The trunk is permanent and supports the arms of the grape vine.
The TrunkThe
trunk, which was formerly an individual shoot trained as the trunk in a
young vine, becomes permanent and supports the above-ground vegetative
(leaves and stems) and reproductive (flowers and fruits) structures of
the vine. The height of the trunk varies with the training system
selected. For cane-pruned training systems, the top of the trunk is
referred to as the head. The height of the head is determined by
pruning during the initial stages of training a young grapevine (or
replacement trunk). The trunk of a mature vine will have arms, short
branches from which canes and/or spurs originate, which are located in
different positions depending on the system. Some training systems
utilize cordons, semi-permanent branches of the trunk. Cordons are
usually trained horizontally along a trellis wire, with spurs spaced at
regular intervals along their length. Where bilateral training systems
are used, the cordon is trained to either side of the trunk, and some
growers refer to each of the two sides of the cordons as arms. Other
systems utilize canes, one-year-old wood arising from arms and usually
located near the head of the vine. Multiple trunks are often used in
grape growing regions that are at risk for winter injury. The term
“crown” refers to the basal region of the trunk slightly below and
above the soil level.
Shoots and CanesThe
shoot consists of stems, leaves, tendrils, and fruit and is the primary
unit of vine growth and the principal focus of many vineyard management
practices. Shoots arise from compound buds that are initiated around
bloom during the previous growing season. Each compound bud can
potentially produce more than one shoot. Primary shoots arise from
primary buds (described below) and are normally the fruit-producing
shoots on the vine. The main axis of the shoot consists of structural
support tissues and conducting tissues to transport water, nutrients,
and the products of photosynthesis. Arranged along the shoot in regular
patterns are leaves, tendrils, flower or fruit clusters, and buds.
General areas of the shoot are described as basal (closest to its point
of origin), mid-shoot, and apex (tip). The term canopy is used to
describe the collective arrangement of the vine’s shoots, leaves and
fruit; some viticulturists also include the trunk, cordons and canes.
Shoot tip.
The shoot has many points of growth that will be described in more
detail below, but the main shoot growth in length occurs from the
apical meristem, located at the shoot tip. New leaves and tendrils
unfold from the tip as the shoot grows. Growth rate of the shoot varies
during the season. Grapevine shoots do not stop expanding by forming a
terminal bud as some plants do, but may continue to grow if there is
sufficient heat, soil moisture, and nutrients.
Leaves.
Leaves are produced at the apical meristem. The shoot produces two or
more closely spaced bracts (small scale-like leaves) at its base before
it produces the first true foliage leaf (Pratt, 1974). Leaves are
attached at the slightly enlarged area on the shoot that is referred to
as a node. The area between nodes is called the internode. The distance
between nodes is an indicator of the rate of shoot growth, so internode
length varies along the cane corresponding to varying growth rates
during the season.
Leaves
consist of the blade, the broad, flat part of the leaf designed to
absorb sunlight and CO2 in the food manufacturing process of
photosynthesis, and the petiole, the stem-like structure that connects
the leaf to the shoot. The lower surface of leaf blade contains
thousands of microscopic pores called stomata (singular = stomate),
through which diffusion of CO2, O2, and water vapor occurs. Stomata are
open in the light and closed in the dark. The petiole conducts water
and food material to and from the leaf blade, and maintains the
orientation of the leaf blade to perform its functions in
photosynthesis.
Tendrils.
The shoot also produces tendrils, slender structures that coil around
smaller objects (i.e., trellis wires, small stakes, and other shoots)
to provide support for growing shoots. Tendrils grow opposite a leaf at
the node, except the first two or three leaves at the base of the
shoot. Thereafter, tendrils can be found opposite leaves, skipping
every third leaf. Flower clusters and tendrils have a common
developmental origin (Mullins et al., 1992), so occasionally a few
flowers will develop on the end of a tendril.
Buds. A bud is a
growing point that develops in the leaf axil, the area just above the
point of connection between the petiole and shoot. The single bud that
develops in this area is described in botanical terms as an axillary
bud. On grapevines, a bud develops in every leaf axil, including the
inconspicuous basal bracts (scale-like leaves). In viticulture
terminology, the two buds associated with a leaf are termed the lateral
bud and the dormant bud (or latent bud). The lateral bud is the true
axillary bud of the foliage leaf, and the dormant bud forms in the
bract axil of the lateral bud. Because of their developmental
association, the two buds are situated side-by-side in the main leaf
axil. Each bud is a compound bud, containing three distinct growing
points, each capable of producing a shoot. These are commonly referred
to as the primary, secondary, and tertiary buds, respectively. At bud
burst, the primary bud is typically the only bud that begins to grow.
If the primary bud is damaged, then the secondary and/or tertiary buds
are released from dormancy and grow in place of the primary bud. These
secondary and tertiary buds generally have little to no fruit in
comparison to the primary bud.
Fig. 2
A cross section of a dormant bud. The three buds within the compound bud can be seen.
Suckers and Watersprouts.
Latent buds embedded in older trunk and cordon wood may also produce
shoots. Suckers are shoots that grow from the crown area of the trunk.
Watersprout is sometimes used to refer to a shoot arising from the
upper regions of the trunk or from cordons (Winkler et al., 1974). Buds
growing from older wood are not newly initiated buds, but rather they
developed on green shoots as axillary buds that never grew out. These
latent buds can remain dormant indefinitely until an extreme event such
as injury to the vine or very severe pruning stimulates renewed
development and shoot growth (Winkler et al., 1974).
Suckers
often arise from latent buds at underground node positions on the
trunk. In routine vine management, suckers are removed early in the
season before axillary buds can mature in basal bracts of the sucker
shoots. Similarly, above-ground suckers are typically stripped off the
trunk manually so a pruning stub does not remain to harbor additional
latent buds that could produce more suckers in the following year.
Latent
buds come into use when trunk, cordon, or spur renewal is necessary.
Generally, numerous latent buds exist at the “renewal positions” (a
pruning term) on the trunk or cordons. Dormant secondary and tertiary
buds exist in the stubs that remain after canes or spurs have been
removed by pruning.
Canes. The shoot enters a transitional
phase, starting around veraison, when it begins to mature or ripen.
Shoot maturation begins at the shoot base as periderm develops,
starting at the shoot base, appearing initially as a yellow, smooth
“skin”, and continues to form outward toward the shoot tip through the
remainder of summer and fall. As periderm develops, it changes from
yellow to brown, and becomes a dry, hard, smooth layer of bark. During
shoot maturation, the cell walls of ray tissues thicken and there is an
accumulation of starch (storage carbohydrates) in all living cells of
the wood and bark (Mullins et al., 1992). Once the leaves fall from the
vine at the beginning of the dormant season, the mature shoot is
considered a cane.
The cane is the principal structure of
concern in the dormant season, when pruning is employed to manage vine
size and shape, and to control the quantity of potential crop in the
coming season. Because a cane is simply a mature shoot, the same terms
are used to describe its parts. Pruning severity is often described in
terms of the number of buds retained per vine or bud count. This refers
to the dormant buds, which in a single bud contains three growing
points as described above. When considering a dormant cane, the buds
located at the very base of a cane include secondary and tertiary
growing points that give rise to the axillary buds of the shoot’s basal
bracts (Pratt, 1974). It should be noted that the most basal buds on a
cane are generally not fruitful and do not grow out, so they are not
included in bud counts. These are often referred to as non-count buds
during the pruning process.
Canes can be pruned to varying
lengths, and when they consist of only one to four buds, they are
referred to as spurs, or often, fruiting spurs. Grapevine spurs should
not be confused with true spurs produced by apple, cherry, and other
fruit trees, which are the natural fruit-bearing structures of these
trees. On grapevines, spurs are created by short-pruning of canes.
Training systems that use cane-pruning also use spurs for the purpose
of growing shoots to be trained for fruiting canes in the following
season. These spurs are known as renewal spurs, indicating their role
in replacing the arms.
Reviewed by Tim Martinson, Cornell University and Patty Skinkis, Oregon State UniversityReferences:
Mullins, M. G., A. Bouquet, and L. E. Williams. 1992. Biology of the Grapevine. Cambridge University Press.
Pratt, C. 1974. Vegetative anatomy in cultivated grapes. A review. American Journal of Enology and Viticulture 25:131-150.
Winkler,
A.J., J.A. Cook, W.M. Kliewer, and L.L. Lider. 1974. General
Viticulture. University of California Press. Berkeley, California.