Agriculture Reference
In-Depth Information
Table
.
Direct, residual and cumulative effects of shade on fruit set ( fruits harvested
per
blossom clusters) 'Cox's Orange Pippin'/'M.
' apple
Light (% daylight) in and
Light
Light
Fruit set
.
is the of the difference from the never-shaded control.
Data from Jackson and Palmer (b). Reproduced with permission.
They found that exogenous ethephon, an ethylene-generating compound, in-
creased the rate of seed abortion and fruit abscission while application of AVG
(aminoethoxyvinyl glycine), which inhibits ethylene biosynthesis, reduced the
rate of seed abortion, cellulase activity in the abscission zone, and fruit abscis-
sion as well as preventing ethylene evolution. Other studies showed AVG to
reduce endogenous ethylene production and increase fruit set of 'Delicious'
(Greene,
) and fruit set of 'Cox' apples (Child and Williams,
) and
'Comice' pear (Lombard and Richardson,
b)
found that for 'McIntosh Red' apples subjected to high night temperatures,
beginning on the
). However, Fukui
et al.
(
th day after full bloom, the check to growth that preceded
fruit drop also preceded ethylene evolution and the formation of an abscission
layer. They concluded that ethylene was not the primary factor in inducing the
drop. Also, Kondo and Takahashi (
) did not find much effect of AVG on
shade-induced apple fruitlet shed. Fruit size and shape are adversely affected
by early AVG application, so it has not become a commercial fruit-setting
agent although used as a pre-harvest 'stop-drop'.
Ethephon application frequently induces fruitlet shed and although effects
are inconsistent it is widely used as a fruit thinning agent, applied at blossom
time or later (Wertheim,
).
Effects of shade and photosynthesis on fruit set
Artificial shading reduces fruit set of apples both in the year of shading and in
the following year (Table
b). Fruit set is reduced
linearly as light intensity within a mature apple tree canopy declines over the
range from
.
; Jackson and Palmer,
).
Heavy shading for only a few days within the period from about
%to
% of full sunlight (Rom,
to
days after full bloom induces fruit shed (Kondo and Takahashi,
;
Beruter and Droz,
). Shading earlier or
later is ineffective. Fruitlets induced to abscise by shading stop growth within
;Byers
et al.
,
; Stopar,
-
days of shading and shed
-
days later (Byers
et al.
,
). Application
