The 41-day period of cold temperature regime during young
fruit growth (from 28 to 68 days after anthesis) extended the
duration of fruit growth by 35 days (Fig. 6). Fruit growth under
the cold temperature regime was much slower than under the
warm temperature regime, and only after temperature rose to the
warm regime did the fruit growth recover to a rate comparable
to that of the fruit constantly exposed to the warm temperature
regime (Fig. 6A and C). No compensatory faster fruit growth was
observed after the temperature rise, and the final fruit weight of
cold-exposed fruit was significantly smaller than that of fruit grown
in warm temperatures. When traced against temperature time,
fruit growth pattern under the two temperature regimes was pretty
similar (Fig. 6B and D). However, the difference in fruit size between
the twotemperature regimes increased as fruit matured, which was
very similar to the result of the field observation (Fig. 3). The above
results suggested that exposure of young fruit to cold temperatures
of below 15
◦
C in Stage I reduced fruit growth potential.
In trees grown in the warm phytotron, fruit drop was intensive
in the early stage of fruit development (before 37 days after
anthesis) and after initiation of aril growth (69 days after anthesis)
(Fig. 7A). During the cold period, fruit drop in the cold-exposed trees
was slight but became intensive after temperature rise (Fig. 7A),
which is in agreement with field observations. The pattern of cumulative
fruit drop rate with temperature time was similar in both
temperature treatments, and there was almost no difference in
final fruit drop rate. Hence, the cold temperatures in early fruit
development delayed fruit drop until temperature rise, and it
did not induce excessive fruit drop compared to the warm control.
Trees exposed to cold had a slightly higher fruit cracking
incidence than those grown under the constant warm temperature
regimes, although no significant difference between
the treatments was found (15.3% vs 9.2%, p > 0.05) (results not
shown).