Vergara - 1976 - Physiological and morphological adaptability of ri

TEMPERFYTLTRE AND LIGHT. REPRODLT(.‘TI\-'E GROWTH AND RIPENING 201
stage. as compared with that at [-20] stage, shows slow decline in the low telnperature
range, but rapid decline in the higher temperature range. Munakata
et al. (1967), following soxving-date experiments with many riee nineties. stated
that the optimum temperature for ripening grade wab 20°—23°C on an average
for 3U days after heading time. This result is in good agreement with that in Fig.
10B.
While there are many evidences that the optimum temperature at ripening
stage in phytotron experiments is lower than that in field expeiiments.
Matsushima et al. (19641) found that when the riee plants were treated with
temperature levels of 16°. 21°. 31°, and 36°C for l5 days at most active ripening
stage in the phytotron. the optimum temperature for ripening grade ranged from
l6°to 21°C.
It is well known that low light intensity brings about the decline in optimum
temperature (Fig. ll). That the light intensity is even 50% loxver than outdoors
is frequently observed in a phytotrcin. However, the fact that optimum temperature
for ripening is l6°—21°C in phytotron experiments cannot be fully explained
by the low light intensity, because the shifting of optimum temperature
by lower light intensity is not so large, as shown in Fig. 10B. From phytotron
experiments, it may be true that japonica riee has a low optimum temperature
such as l6°—20°C, although the ripening period may be considerably prolonged.
Actual value of
2O
ripening grade (mg)
l5 —
I
I
I
\
I .
O
O _ O
O
O
. I r1088
n= I60
5 -,°
I
5 IO l5 2O
Estimated value t
mq)
11. Correlation diagram between actual and estimated
values of ripening grade. Ripening grade = kernel yield
number of spikelets (mg). Model: type IV. three stages,
Data for 1962-71, 20 prefectures.
l