Agriculture Reference
In-Depth Information
Continuous rain prevents both the diurnal depression in
ψ
w
and contraction
of fruits. Most studies have shown that the greater part of the shrinkage is a
result of water moving out of the fruit back through the pedicel in equilibration
with the water tensions in the conducting system (Lang and Volz,
). In
some cases the major part of the water loss is by direct evaporation from the
fruits themselves ( Jones and Higgs,
) but the re-expansion at night must
depend on the balance of water potentials.
Fruit pedicels have low hydraulic conductance. Especially for some cultivars
and late in the season, the xylem becomes largely non-functional and water
movement into the apple is largely through the phloem. This is important in
relation to calcium fluxand was discussed in Chapter
.
Fruit surface (skin) conductance varies between cultivars, being higher in
russeted cultivars than those with waxy skins.
Integrated effects of water stress
Fruit set can be very adversely affected by levels of water stress too mild to
have any adverse influence on shoot extension growth (Powell,
). Under
many environmental conditions this may, however, not cause a problem as soil
moisture levels in the early part of the season are high because of winter rains
or frost-protection irrigation. The severe effects of water deficits on fruit bud
formation under some circumstances (Landsberg and Jones,
) may not be
evident in many areas for the same reason.
The greatest effect of reduced water supply on the vegetative growth and
dry matter production by fruit trees is that which arises through the reduction
of leaf area per tree (Table
.
). Root growth is much less affected so the
root/shoot ratio is increased.
Effects of water supply on leaf area (m
/tree) and dry
weight of leaves, stems, fruits and roots (g) of fruiting trees of 'Golden
Delicious'/'M.
Table
.
'
Water rate (%)
Leaf area
.
.
.
Leaf dry weight
Stem dry weight
Fruit dry weight
Root dry weight
Calculated from data of Buwalda and Lenz (
).
