Agriculture Reference
In-Depth Information
defined the pattern of dry matter accumulation as consisting of two linear
phases. The first of these is of very low growth, lasting about
days, and the
second of steady linear growth at a rate of
.
-
.
g dry weight per day up
to harvest. Lakso
et al.
(
) found that the growth of 'Empire' and 'Golden
Delicious' apples showed a positive curvilinear growth curve in the early part
of the season (from
days, depending on cultivar and environment)
followed by a much more rapid linear growth phase up to harvest. This growth
pattern can be described by an expolinear equation, two key elements in which
are the time from anthesis to the intercept of the linear growth phase and the
slope of this phase. They found the former to be temperature-sensitive and
the latter to be dependent on the number of cells in the cortex, in the limited
number of cases considered.
Tukey and Young (
to
) found that in New York State the growth curve of
the entire fruit is nearly linear up to ripening and harvest of the early summer
apple'EarlyHarvest'.Forsuccessivelylatercultivars,including'McIntosh'and
'Rome', the curve flattens as the season progresses. The shape of the growth
curve is thus a cultivar characteristic although it is modified by climate and
the degree of between-fruit competition.
In general terms the major determinants of variability in fruit growth are
cell division before anthesis and cell expansion after this, with cell division
post-anthesis making a smaller contribution (Coombe,
).
Effects of pre-bloom factors
The importance of cell division before blossoming as a determinant of the total
numberoffruitcellssuggeststhatpre-bloomfactorsshouldhaveaconsiderable
effect on fruit size. This effect appears to provide a rationale for much of the
between-season and within-tree variability in fruit growth and size.
Bergh (
b) compared flower and fruit development on 'Starking' apple
trees which had been thinned to give a normal crop load with that on trees
which had been unthinned and consequently bore very heavy crops. The
number of cells in the cortical tissue at the base of the developing flowers was
reduced by heavy cropping, the reduction being already evident
weeks after
the onset of differentiation of the sepal primordia (Table
). The effect on
cell number at full bloom was followed by a somewhat smaller effect on fruit
size at harvest. Although the decrease in cell numbers of fruits following heavy
cropping was accompanied by larger cells, these did not compensate for the
effect of reduction in cell numbers. In most cases this is not so and fruits in
an 'off' year following a heavy crop are large, but not as large as would be
expected based on the very light crop.
.
