Agriculture Reference
In-Depth Information
ethylene production (Kondo and Takahashi,
). However, Rahemi
et al.
(
) did not find differences in set between some other cultivars to be related
to their ethylene production. The 'Red Delicious' group as a whole shows a
number of other features associated with their fruit setting problems (Dennis,
).
Poor fruit set in 'Packham's Triumph' pear is primarily related to exces-
sive competition between shoots and fruits in young, vigorously growing trees
and fruit-fruit competition in older 'spur-bound' trees (van Zyl and Strydom,
). In this cultivar in the absence of appropriate pruning to reduce the
number of growing points and spurs, very heavy flowering can be associated
with unsatisfactory fruit set. Similarly, severe pruning of 'Comice' improves its
fruit set (Parry,
) but this cultivar, unlike 'Packham's Triumph', also has
a short EPP. For a number of pear cultivars with a natural tendency towards
parthenocarpy, set can usually be improved by the use of gibberellin sprays to
increase the set of seedless fruits.
Fruit growth
A fruit can be defined as 'the edible product of a plant or tree, consisting of the
seed and its envelope, especially the latter when juicy and pulpy' (
Oxford English
Dictionary
). Understanding fruit growth, however, requires consideration of the
growth of the flower prior to seed formation and must also encompass the case
of parthenocarpic, seedless fruits.
Two separate processes are involved in fruit growth: cell division and cell
expansion.
Cell division
There are two million cells in the flesh of an apple at anthesis and
million at
harvest (Pearson and Robertson,
). To achieve this number,
doublings
are required before anthesis and only
).
All these figures must be regarded as approximations but they illustrate a
general point.
Most of the post-anthesis cell divisions occur within the first few weeks after
blossoming. Schechter
et al.
(
.
doublings after this (Coombe,
a, b) found that the percentage of dividing
cells in 'Idared' apples peaked at about
days from full bloom, when about
% of the cells were dividing. It then decreased for about
days to
-
%,
which continued up to
days from full bloom. Bain and Robertson (
)
reported that cell division in 'Granny Smith' apple is completed within
weeks
of full bloom in Australia, and Denne (
) found it to last for
-
weeks in
'Cox' and unthinned 'Miller's Seedling' but for about
weeks in 'Miller's
Seedling' thinned at the pink-bud stage in England.
