Yoshida und Hara - 1977 - Effects of air temperature and light on grain fill

96 s. YOSHIDA <strong>and</strong> T. HARA
<strong>temperature</strong> was varied from 16° to 34°0 with a constant night <strong>temperature</strong> <strong>of</strong> 16°0;
thus, the daily mean <strong>temperature</strong> ranged between 16° <strong>and</strong> 25°0.
Experiment 4. Effict oj <strong>temperature</strong> <strong>and</strong> <strong>light</strong> on grain filling. Two levels <strong>of</strong> <strong>light</strong> intensity
(low <strong>light</strong>=36 cal· cm- 2 • day-I; high <strong>light</strong>=1l4 cal· cm- I • day-I) were
combined with two levels <strong>of</strong> <strong>temperature</strong> (23°/15°0 <strong>and</strong> 32°/24°0). The low <strong>light</strong>
intensity was achieved by placing a mesh screen beneath the bank <strong>of</strong> <strong>light</strong>s.
RESULTS
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Effect oj the daily mean <strong>temperature</strong> on grain filling
Grain growth curve. Five daily mean <strong>temperature</strong>s (Table 1) were used, but in this
coverage data will be presented for only three daily mean <strong>temperature</strong>s (16°, 22°, <strong>and</strong>
28°0). The slope in the grain growth curve suggested that the rate <strong>of</strong> grain filling was
faster at the higher <strong>temperature</strong> in both varieties (Fig. 1). Additionally, the grain
filling period was shorter at the higher <strong>temperature</strong>s for both varieties <strong>of</strong> rice. The
leaves <strong>of</strong> IR20 rice turned yellow within 24 hours only after the plants were subjected
to daily mean <strong>temperature</strong> <strong>of</strong> 16°0, indicating that day <strong>temperature</strong> <strong>of</strong> 20°0 is subnormal
for leaf activity, i.e., photosynthesis (14) <strong>and</strong> others. Grain filling at this
<strong>temperature</strong> was very slow, but the final grain weight was similar to that achieved <strong>und</strong>er
the 22°0 <strong>and</strong> the 28°0 regimes. The duration <strong>of</strong> grain filling period, defined as number
<strong>of</strong> days required to reach the maximum weight, was 13 days at 28°0 <strong>and</strong> 33 days at
16°0 for IR20 rice.
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Effect <strong>of</strong> <strong>temperature</strong> on grain growth <strong>of</strong> IR20 <strong>and</strong> Fujisaka riel'S.
Leaves <strong>of</strong> Fujisaka 5 rice remained green even at a daily mean <strong>temperature</strong> <strong>of</strong> 16°C.
The grain growth curve <strong>of</strong> Fujisaka 5 at 16°0 was characterized by a long lag-phase
following a linear phase. At a daily mean <strong>temperature</strong> <strong>of</strong> 28°C, the grain weight
declined after the peak weight was reached, <strong>and</strong> the final grain weight was about 15