Agriculture Reference
In-Depth Information
In pear, Toyoma and Hayashi (
) reported cell division in early cultivars
to last for
-
days post-bloom and for
days for late cultivars. Sterling
(
) found cell division in 'Bartlett' pear to last for
-
weeks in the bulk
flesh and
weeks at the periphery.
Cell expansion
Cell enlargement begins soon after pollination, continues through the cell
division period and, at a diminishing rate, until harvest (Denne,
). The
increase in cell size involves deposition of new cell wall material, influxof sol-
utes, influxof water which depends on solute concentration, cell wall plasticity,
water availability, transpiration and plant water potential, and the constraints
imposed on the flesh by the extensibility of the skin and other surrounding
layers.
During and shortly after anthesis the ovary is dependent on the overall level
of reserves for its nutrient supply and has limited capacity to attract these
(Coombe,
). Once the fruit has commenced growth, hormones produced
intheseedsandfleshareimportantinmobilizingresources.Themainsupplyof
organiccompoundsimportedintothefruitisthenfromcurrentphotosynthesis.
Apple leaves produce sorbitol and to a lesser extent sucrose, sorbitol being
the main transport carbohydrate. The photosynthates imported into the fruit
are used in the synthesis of structural polysaccharides for growth, respiration
and storage of carbohydrate (Beruter and Studer Feusi,
). They are also
metabolized into fructose, sucrose, malic acid and starch (Beruter
et al.
,
).
Fructose makes the greatest contribution to the fruit solute potential of both
'Cox's Orange Pippin' and 'Golden Delicious' apples but sucrose is the major
soluble carbohydrate on a dry weight basis in 'Cox's Orange Pippin' (Pavel
and De Jong,
% of the total
fruit solute potential in 'Golden Delicious' early in the season and about
). Soluble carbohydrate contributes about
%
at harvest.
Overall fruit growth
Early studies, e.g. by Denne (
) on 'Cox's Orange Pippin', showed
a typical single-sigmoid growth curve. For convenience of comparison this
could be divided into three phases: a slow increase in weight for the first
,
-
days after pollination, a phase of rapid exponential increase lasting for
weeks, and a phase of progressive slowing of the rate of increase leading
up to harvest. Orlandini
et al.
(
-
) found that increases in diameter always
followed a sigmoid curve in
sets of data on 'Golden Delicious'.
a, b) found little evidence for slowing down of
'McIntosh', 'Delicious', 'Empire' and 'Idared' growth towards harvest and
Schechter
et al.
(
