Agriculture Reference
In-Depth Information
in a shorter growing season, of the improvement in fruit set and conse-
quently greater fruit-fruit competition or of an effect on pre-bloom cell di-
vision. Hamer (
) found that apple buds subjected to evaporative cooling
have lower dry weights than those on control trees at the later stages of bud
development.
Post-bloom effects
Fruit growth appears to be dependent on seeds only for the first
weeks or so
after petal fall (Abbott,
).
The effect of seeds on growth is particularly obvious in fruits with a very
uneven shape associated with the presence of seeds only in locules on one side
of the fruit. Similar asymmetry can be induced by localized GA application
(Bukovac and Nakagawa,
).
Fruit growth and final fruit size may be greater the higher the number of
seeds (Denne,
). The effect of seed number on the percentage increase in
fruitlet diameter is confined to the first
days after blossoming
although proportional differences established by that time are carried through
to harvest. The total number of cells per fruit increases with seed number but
there is no consistent relationship between seed number and cell size. The
ratio of fruit diameter to length increases with increasing seed number in both
apple and pear (Denne,
weeks to
).
In those cultivars which can be induced to set parthenocarpic fruits by
exogenous hormone application the complete cycle of fruit growth, extending
for several months, is obtained by a single application at around the time
of anthesis. This suggests that the hormones simply act as inducing agents
(Goodwin,
). Subsequent growth is associated with a pattern of hormone
activity in the developing fruit which is similar in both parthenocarpic and
seeded fruits (Gil
et al.
,
). Auxins, cytokinins and gibberellins have
all been identified in apple and pear fruit flesh (Gil
et al.
,
,
,
; Goodwin,
). The cytokinins found in fruits are not
necessarily synthesized there: they are found in xylem sap and it is possible
that root-produced cytokinins are transported to fruits.
Applicationofgibberellinsandofbenzyladenine(
; Letham and Williams,
-BA)increasestheratioof
applelengthtodiameterandthedevelopmentofenlargedcalyxlobes(Letham,
). Elongated apples
with pronounced calyxlobes are considered to be typical, therefore desirable,
for 'Red Delicious' and in warm areas fruits that are not hormone-sprayed
tend to be too round.
; Williams and Stahly,
; Greenhalgh
et al.
,
