Agriculture Reference
In-Depth Information
Table
.
Effects of shade on fruit colour. 'Cox's Orange
Pippin'/'M.
'
Shade level % full daylight
Average % surface coloured red
.
.
.
.
Mean colour intensity
.
.
.
.
=
=
(
green,
dark red)
Data from Jackson
et al.
(
). Reproduced with permission.
(Table
). The effect is proportional to the degree of shading. From associ-
ated measurements on the fruits ( Jackson
et al.
,
.
) it is likely that the effect
on red colour is due not only to direct effects of light intensity on the skin but
also to effects on fruit carbohydrate content.
Within individual trees and in hedgerow orchards fruits from tree zones
well exposed to light have a higher proportion of their fruit surface coloured
red than fruits from shaded zones ( Jackson
).
The concentration of anthocyanin in the most highly coloured skin areas is
also a function of the light intensity under which the fruit is grown ( Jackson
et al.
,
b,
; Jackson
et al.
,
). Even under the high light intensities of Washington State, USA,
% of within-tree variation in percentage red fruit colour was accounted
for by a curvilinear regression on light intensity, with colour increasing up to
approximately
mol m
s
−
(Barritt
et al.
,
b).
Reduction in fruit colour as a result of shade is the major factor determining
depth of productive canopy, hence potential economic yield, in many fruit-
growing areas. Jackson (
% full sunlight, i.e.
µ
b) found that under English conditions 'Cox'
apples with more than
% of their surface coloured red were not generally
found below a leaf area indexof more than
, giving an effective canopy
volume much smaller than that which can produce fruits of adequate size. In
such cases colour sports requiring less light for adequate colour development
are very valuable. Some cultivars are particularly sensitive to shade. Arakawa
et al.
(
.
) found that 'Fuji' apples produce much less anthocyanin at any given
light level than 'Starking Delicious' and at low light levels within the canopy
'Fuji' fails to develop adequate colour. If, however, colour sports produce good
colour at very low light intensities the accepted link between amount and
intensity of colour and fruit composition is broken and red colour no longer
guarantees good eating quality (Seeley
et al.
,
).
The main effects of temperature on fruit colour occur late in the season
when, in many fruit-growing areas, temperatures are falling. Curry (
)
