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

98 S. YOSHIDA <strong>and</strong> T. HARA
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daily mean <strong>temperature</strong> range <strong>of</strong> 16° to 28°C, the higher was the <strong>temperature</strong>, the higher
was the percent <strong>of</strong> nitrogen. Curves for the accumulation <strong>of</strong> nitrogen per grain are
basically similar to those for dry weight; the higher was the <strong>temperature</strong>, the faster the
nitrogen accumulated in the rice grains. The variation in the percent nitrogen among
the three <strong>temperature</strong> regimes was greater than that <strong>of</strong> the nitrogen accumulated per
grain. However, because the weight per grain <strong>of</strong>IR20 was lower than that <strong>of</strong> Fujisaka
5, IR20 rice contained less nitrogen per grain, but contained a higher percent nitrogen
than did Fujisaka 5.
Changes in water content in the grains. During the initial phases <strong>of</strong> the grain filling
period the water content <strong>of</strong> the grains was about 58 percent <strong>and</strong> then declined to less
than 17 percent during the later stages <strong>of</strong> development (Fig. 3). The rate <strong>of</strong> this decrease
in water content with maturity increased with the increase in the <strong>temperature</strong>
regime. The water content <strong>of</strong> grains at the time <strong>of</strong> maximum grain weight, in general,
ranged from 19 to 24 percent, but it was 29 percent for IR20 rice grains when the daily
mean <strong>temperature</strong> was 16°C.
Grain weight <strong>and</strong> grain quality. Based on data collected from whole panicle grains,
the optimum daily mean <strong>temperature</strong> for maximum weight per grain appeared to range
between 19° <strong>and</strong> 25°C for IR20 rice <strong>and</strong> 16° to 22°C for Fujisaka 5 (Table 1). In IR20
rice the grain weight <strong>of</strong> upper branches at a daily mean <strong>temperature</strong> <strong>of</strong> 16°C did not
differ appreciably from that obtained at a daily mean <strong>temperature</strong> <strong>of</strong> 22°C (Fig. 1), but
the average grain weight <strong>of</strong> the whole panicle at 16°C was significantly lower than that
at 22°C. This was because at 16°C the grains <strong>of</strong> the upper branches matured normally
but those <strong>of</strong> the lower branches were not mature at harvest. The lowest weight per grain
for IR20 rice occurred with a daily mean <strong>temperature</strong> <strong>of</strong> 16°C, while that for Fujisaka
5 occurred with a daily mean <strong>temperature</strong> <strong>of</strong> 28°C. IR20 rice appeared to be sensitive
to a low daily mean <strong>temperature</strong> while Fujisaka 5 appeared to be sensitive to a high
daily mean <strong>temperature</strong>. Similarly, the maximum amount <strong>of</strong> chalky grains in IR20
rice occurred at 16°C, while this was true for Fujisaka 5 rice at 28°C. A lower weight
per grain seemed to be associated with a higher percentage <strong>of</strong> chalky grains. Green
grains were fo<strong>und</strong> with all three <strong>temperature</strong> regimes with IR20 rice, but they were
fo<strong>und</strong> only at 16°C with Fujisaka 5 rice. Additionally, the brown rice <strong>of</strong> IR20 became
red brown in color when the daily mean <strong>temperature</strong> ranged between 16° <strong>and</strong> 22°C.
Effect oj night <strong>temperature</strong> on grain weight <strong>and</strong> grain quality
Within a range <strong>of</strong> night <strong>temperature</strong>s <strong>of</strong> 14° to 32°C with a constant day <strong>temperature</strong>
<strong>of</strong> 32°C, the grain weight among the different <strong>temperature</strong> regimes was similar,
except when the night <strong>temperature</strong> for Fujisaka 5 rice was HOC (Table 2). The daily
mean <strong>temperature</strong> <strong>of</strong> the 32°/14°C <strong>temperature</strong> regime was 23°C which should have
been optimum for maximum grain weight <strong>of</strong> Fujisaka 5 rice (Table 1). Apparently,
the large difference (l8°C) between the day <strong>and</strong> night <strong>temperature</strong>s had an adverse
effect on the ripening <strong>of</strong> Fujisaka 5 rice plants. The large difference in the day <strong>and</strong>
night <strong>temperature</strong>s had little effect on the grain weight <strong>of</strong> IR20 rice.