The duration of fruit growth in over-winter off-season fruit was
longer than in on-season fruit (166 days vs 106 days in 2004–2005)
(Fig. 2A). Fruit weight increase was slow during the early period of
development with slow growth of the pericarp and the seed (Fig. 2B
and D), and became faster in the later period with the rapid growth
of the aril and the seed (Fig. 2C and D). Hence, fruit growth could
be roughly divided into two stages: Stage I was characterized by
the slow growth of pericarp and seed coat, and Stage II by rapid aril
and seed growth. The turning point occurred on 52 and 117 days
after anthesis in on-season and off-season fruits, respectively. The
longer growth duration of off-season fruit resulted almost entirely
from a longer Stage I. Off-season fruit at harvest were smaller with
significantly smaller pericarp and aril. However, seed size of offseason
fruit was comparable to that of the on-season fruit.
Fruit growth plotted against temperature time (
D) in both seasons
perfectly matched cubic curves, and the difference in fruit
weight between on-season and off-season longan became greater
towards harvest at later stages (Fig. 3).
◦
In off-season longan, all the major cold spells occurred during
Stage I and the average daily temperature in this stage was
16.6
C for both 2004–2005 and 2007–2008 periods, much colder
than that in Stage II, which was 23.8 and 24.4
◦
C for 2004–2005 and
2007–2008, respectively. In on-season longan, the average daily
temperature during Stage I was around 25
◦
◦
C, only about 2
C cooler
than that in Stage II. The effective accumulative temperature during
Stage I in off-season longan was slightly lower than in on-season
longan in 2004–2005 (886.2
◦
D vs 901.3
D), but it was higher in
2007–2008 (971.6
◦
D vs 757.6
◦
◦
D). In both crop years, the effective
accumulative temperature during Stage II was lower in off-season
longan than in on-season longan (Table 1). The results suggest that
the long-term exposure to low temperatures during Stage I might
lessen the demand for heat units in Stage II.
Fruit development in the off-season longan, especially in Stage
I, was exposed to drier conditions than that of on-season longan.
In respect to different years, humidity during fruit development in
2004–2005 was lower than in 2007–2008 (Table 1).