Agriculture Reference
In-Depth Information
Trunk and Cordons
The trunk and cordons carry the vascular tissues that provide structural support and
transport water as well as essential nutrients through the vine. The trunk and cor-
dons may also store some carbohydrate and mineral reserves.
The Canopy
The shoots of the grapevine consists of nodes and internodes and a growing shoot
tip. After leaf abscission in autumn the shoots are referred to as canes. At each node,
a bud is located just above the leaf petiole and these contain the partially developed
shoots and inflorescences for the following season. Inflorescences (usually two per
shoot) form at the third to sixth nodes from the base of the shoot. Tendrils have the
same ontogenetic origin as inflorescences but their role is to attach shoots to stable
structures so that the growing shoot tip is able to grow toward the light. In their
natural state, grapevines are vigorous climbing lianas that can climb up trees to
enormous heights.
The leaves of grapevines most often have a palmate shape with five main vascu-
lar bundles. The edges of the leaves are usually serrated with variety differences in
the degree of their sharpness. The leaves follow an alternating pattern on the shoot
with a single leaf at each node on the two opposing sides of the shoot (Mullins
et al.
1992
). The leaves carry out the critical process of photosynthesis where light
energy is converted to chemical energy. When young, leaves import carbon to sup-
port expansion and development but as they mature the leaves become net carbon
exporters. Young, fully expanded leaves will undergo maximal photosynthesis for
several weeks, but as they age photosynthesis begins to decline (Fig.
7.3
).
Grapevine leaves have stomata, or pores, scattered on the bottom epidermal layer
through which gas exchange occurs (Fig.
7.3
). Stomata are responsible for CO
2
entry and water vapour loss in the process called transpiration. Grapevine stomatal
density (the number of stomata per unit of leaf area) is responsive to environmental
factors such as light, atmospheric CO
2
concentration as well as root-zone tempera-
ture (Rogiers et al.
2011a
).
Source-Sink Interactions
A carbon source may be a photosynthetically active leaf or a root full of stored
starch while a sink is an area where the carbon is used for respiration and the main-
tenance of existing biomass, or for growth such as in developing shoot tips. The
grape bunches are another strong sink, especially after veraison, while the roots
become a strong sink during the periods of active root growth and carbohydrate
reserve replenishment. Sink feed-back mechanisms exist to co-ordinate the supply
and demand of carbohydrates (Wardlaw
1990
). For instance, the removal of berries
