Agriculture Reference
In-Depth Information
Table
.
Effects of treatments which induced large differences in fruit yields in
on cropping and growth in
and
. 'Cox's Orange Pippin' apples
with results averaged over
rootstocks
Treatments in
P
C
t
T
Significance
Fruits per tree
***
Fruit yield, kg/tree,
. . . .
***
Fruit yield, kg/tree,
.
.
.
.
***
Mean shoot length cm,
.
. .
.
*
Mean shoot length cm,
.
.
. .
***
a
Relative girth increment
.
.
.
.
***
a
Relative girth increment
.
.
.
.
NS
a
Calculated as log
e
girth
/
end of year
−
log
e
girth
/
beginning of year,
which also gives a measure of relative growth rate.
P, Hand-pollinated, C, control; t, lightly thinned; T, heavily thinned.
Data from Blasco ( ). Reproduced with permission.
removal of unexpanded tip leaves caused an immediate reduction in length of
internodes produced and the latter workers related this to the high GA content
of the leaves removed.
Root system size and function has a dominant effect on shoot growth. This is
found, as discussed earlier, when the shoot system is grafted on to an inherently
dwarfed root system, when root system size is reduced by root pruning or
constrained by growing it in a root-restriction nylon container. Although the
response to root pruning may involve checks to shoot growth as a result of
competition from compensatory root growth, the effects of the genetically-
limitedrootstocksandofrootrestrictionmembranesunderconditionsofample
water and nutrient supply suggest an intrinsic hormonal control mechanism
(cf. pp.
).
Fruiting results in diversion of metabolites from vegetative growth, includ-
ing shoot growth, to fruits (Maggs,
-
). Although the effects can be shown
within a single season (Avery,
), the effect of crop on shoot numbers and
on average shoot length is usually greater in the following season. This has
been shown by experiments in which different levels of cropping were induced
(Table
). Regression studies of the relationship between year-to-year varia-
tions in shoot growth and those in fruit yield have shown either no correlation
in the same season but a major adverse effect of fruit yield on shoot growth
in the following year (Rogers and Booth,
.
), or approximately equal neg-
ative effects of cropping on shoot growth in the same and the following year
(Barlow,
b). The direct (same season) effect may simply reflect competi-
tion for currently available resources, which may be influenced by the lower
