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

104 S. YOSHIDA <strong>and</strong> T. HARA
Downloaded by [Universitaetsbibliothek Giessen] at 15:43 06 April 2015
grain filling period. The present findings indicate that low <strong>light</strong> intensity extends the
grain filling period <strong>of</strong> the grains <strong>of</strong> the whole panicle by about 5 days by affecting the
filling <strong>of</strong> the grains on the lower branches <strong>of</strong> the rice panicle. Light intensity did not
affect the length <strong>of</strong> the grain filling period <strong>of</strong> the grains on the upper branches <strong>of</strong> the
rice panicle.
For field rice crops in the tropics, where the daily mean <strong>temperature</strong> varies between
25° <strong>and</strong> 30°C, the duration <strong>of</strong> ripening is reported to be about 30 days after flowering
(20). The duration <strong>of</strong> ripening is considered the sum <strong>of</strong> the length <strong>of</strong> the grain filling
period for the first-flowering spikelet, difference in days between the first <strong>and</strong> last flowering
spikelets on the same panicle, <strong>and</strong> the duration <strong>of</strong> panicle emergence. In the
present study, the percentage fertility was 94 to 92 percent in IR20 rice <strong>and</strong> 81 to 9(}
percent in Fujisaka 5 rice, when the plants were allowed to remain in the glasshouse
room at 25°C for 3 days after the first spikelet flowering in each panicle. This indicates.
that 3 days are about enough between the time <strong>of</strong> anthesis <strong>of</strong> the first spikelet <strong>and</strong> fertilization
<strong>of</strong> the last spikelet on the same panicle.
Panicle emergence takes 14 days in the field crop <strong>of</strong>IR20 rice at Los Banos, Philippines.
Thus, the sum <strong>of</strong> each term, i.e., (13+3+14), becomes 30 days for an IR20 rice
crop at Los Banos. However, when flowering (or heading) or a rice crop in the field is.
defined in agronomic terms as the time when 50 percent <strong>of</strong> the panicles <strong>of</strong> a rice crop
has emerged, the length <strong>of</strong> the grain filling period for IR20 rice as a field crop at Los.
Banos is 23 days.
The optimum daily mean <strong>temperature</strong> <strong>of</strong> 20° to 22°C (J, 3) reported for the ripening
<strong>of</strong> japonica rice agrees with the results <strong>of</strong> statistical analysis <strong>of</strong> the effects <strong>of</strong> climatic
factors on rice yield (2, 7-9). Despite the fact that different varieties <strong>of</strong> rice, locations~
<strong>and</strong> techniques were used, the optimum <strong>temperature</strong>s reported were remarkably similar.
This may be because in Japan there may not be any differences among japonica
rice varieties in response to <strong>temperature</strong> during ripening. Based on this premise, the
results <strong>of</strong> the present study can be compared with those reported in Japan.
In this study, the optimum daily mean <strong>temperature</strong> for grain filling was fo<strong>und</strong> torange
from 19° to 25°C for IR20 rice <strong>and</strong> from 16° to 22°C in Fujisaka 5 rice. There
appears to be no sharp optimum <strong>temperature</strong> for grain filling, only a <strong>temperature</strong> range
that is optimum for grain filling. In their statistical analyses <strong>of</strong> effects <strong>of</strong> <strong>temperature</strong>
on rice yield, MURATA (9), HANYU et al. (2), <strong>and</strong> MURAKAMI (8) developed similar
parabolic equations in which the daily mean <strong>temperature</strong> <strong>and</strong> solar radiation or sunshine
hours are used as climatic parameters. :Murata's equation is:
r =s [1.20-0.021 (t-21.5)2]
where Y is grain yield (kg/lO a), S<strong>and</strong> t are solar radiation (calc· m- 2 • day-I), <strong>and</strong>
<strong>temperature</strong> (0C), respectively, in August <strong>and</strong> September. When 2BoC is substituted for
t, a 74 percent reduction in yield is obtained as compared with the maximum yield
achieved with a daily mean <strong>temperature</strong> <strong>of</strong>21.5°C. However, our experimental results.
show that the grain weight <strong>of</strong> Fujisaka 5 rice was reduced by only about 11 percent at
28°C as compared with the maximum weight achievable. Recently, MURATA (JO}