Agriculture Reference
In-Depth Information
of AVG does not reduce the effect of short-term shading on shed. There is a
pronounced interaction between unshaded and shaded parts of trees. There
is much less abscission on a single shaded branch on an otherwise unshaded
tree than on the branches of a completely shaded tree and more shed on
an unshaded branch on an otherwise shaded tree than on a corresponding
branch on a totally unshaded tree (Beruter and Droz,
).
Lowered natural light intensity as a result of cloudy conditions prior to June
drop is associated with increased fruit shed both in Akita, Japan and Virginia,
USA (Kondo
et al.
,
;Byers
et al.
,
).
Shading reduces photosynthesis, and both photosynthesis and fruit set
can also be reduced by application of terbacil (
;Byers
et al.
,
-
methyluracil)orotherinhibitorsofphotosynthesis.Thesehavedramaticeffects
on fruit set when applied to leaves between
-tert-butyl-
S
-chloro-
days from full bloom, but
little effect if applied later and no effect if applied to fruits alone (Byers
et al.
,
and
a, b).
Effects of leaf removal on fruit set
Removal of either spur or bourse shoot leaves within
weeks of full bloom
reduces fruit set of 'Cox' and 'Golden Delicious' apples (Proctor and Palmer,
). The effect of reducing both spur and bourse leaves is particularly severe.
Defoliation
days after harvest reduces both initial and final set of
apples in the following year (Tustin
et al.
,
or
), presumably by reducing carbo-
hydrate reserves. The effects of early defoliation may be partly attributable to
its negative effect on subsequent spur leaf size.
Effects of fruit and shoot competition on set
Removal of a large proportion of the flowers results in an increased percent-
age set of those left on the tree (Blasco,
; Knight
et al.
,
; Lauri and
Terouanne,
) removal of a third
of the flower clusters or a third of the flowers within clusters did not reduce
the number of fruits finally harvested, therefore must have led to the retention
of fruits that would otherwise have shed. Reduction of competition leads to
the retention of fruits on inflorescences with a low number of leaves, e.g. on
one-year-old wood (Lauri and Terouanne,
). In some experiments (Knight
et al.
,
).
days after full bloom also reduces June
drop of fruitlets (Quinlan and Preston,
Removal of shoot tips starting
; Makino
et al.
,
). Removal of
shoot tips leads to diversion of photosynthates into the fruitlets.
Signalling through auxin production and movement may be involved in
these competitive effects. Terminal (king) fruitlets are usually less likely to
shed in either the first drop or the June drop than lateral fruitlets within the
