Agriculture Reference
In-Depth Information
were removed within
weeks of petal fall from apple fruits of 'Cox's Orange
Pippin' and 'Crawley Beauty', the fruits would shed. Similar results were ob-
tained with 'Golden Delicious' by Beruter and Droz (
-
). Removal of seeds
after the June drop period, e.g. at
days after full bloom, did not induce any
fruit shed and the fruits continued to grow.
This effect of developing seeds is attributed to the hormones that they
produce. Dennis (
) found that whereas untreated, unpollinated flowers
of 'Wealthy' apple almost all shed, those treated with an extract of immature
'Wealthy' seeds gave normal-sized but seedless fruits. The seed extract was
found to contain gibberellin activity and a similar effect was obtained by
application of the potassium salt of gibberellic acid at
×
−
KGA
. Apple
fruitlets showing the reduced rate of growth characteristics of those about
to shed have lower gibberellin activity in their seeds than those showing the
growth patterns of persistent fruits (Fukui
et al.
,
). High concentrations
of biologically active GAs (GA
,GA
,GA
and GA
) are present in apple
seeds at about
days after anthesis, when the growth rate of the fruit is at
a maximum (Hedden and Hoad,
gibberellins have been
identified in immature apple seeds using GCMS (gas chromatography/mass
spectometry) (Garcia-Martinez and Hedden,
). More than
).
Immature pear seeds of cultivars of
P. communis
,
P. ussuriensis
and
P. serotina
also
contain gibberellins. Removal of the seeds
weeks after full bloom causes the
shed of all fruitlets, but this is largely or completely prevented when gibberellins
are applied to the cut surfaces at the time of seed extraction (Yuda
et al.
,
).
The most effective treatment is with GA
+
even though the principal GA in
the immature seeds is GA
.
Apple seeds contain auxins and cytokinins as well as gibberellins. Con-
centrations of IAA in the seeds, measured by physico-chemical methods, are,
however, low and relatively constant at the endosperm stage, not increasing
until mid-July with the cv. 'Sunset' in England (Hedden
et al.
,
; Hedden
and Hoad,
) found the auxin-like activity in
seeds of 'Starking Delicious' and 'Fuji' to be more or less constant from
). Kondo and Mizuno (
to
a), using histochemical techniques,
found the content of indole derivatives to be very low until
days after full bloom. Fukui
et al.
(
days after full
bloom, increasing between
days after bloom and staying high until
harvest. They also found that fruitlets showing the check in growth charac-
teristic of those about to shed did not differ in indole derivative concentration
from those with a growth pattern characteristic of persistent fruitlets. They
concluded that indole derivatives in seeds have no correlation with early fruit
drop. Auxin can, however, prevent the abscission of apple fruitlets from which
the seeds have been removed (Abbott,
and
) but does not stimulate their further
growth. In this apples differ from a number of other fruits such as tomatoes
and some
Rosa
species.
