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

94 S. YOSHIDA <strong>and</strong> T. HARA
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between the wet season <strong>and</strong> the dry season crop (28), although the <strong>temperature</strong> was
higher during ripening in the dry season than in the wet season (29).
The grain filling period <strong>of</strong> a field rice crop was estimated to range between about
30 days at Los Banos, Philippines to 65 days at Sapporo, Japan <strong>and</strong> Yanco, Australia
(20), based on visual observations <strong>of</strong> the maturity time. Presumably, these large differences
in the length <strong>of</strong> the grain filling period are caused by differences in the <strong>air</strong>
<strong>temperature</strong>. However, there is a dearth <strong>of</strong> reports on the effect <strong>of</strong> <strong>air</strong> <strong>temperature</strong> on
the grain filling period <strong>of</strong> indica rice studied <strong>und</strong>er a well-defined environment.
Solar radiation is the most influential climatic factor determining grain yield during
ripening <strong>of</strong> rice in the tropics (29). Most data on the effect <strong>of</strong> <strong>light</strong> on grain yield
deals mainly with photosynthesis, i.e., supply <strong>of</strong> assimilates to the rice grains, <strong>and</strong> not
with the length <strong>of</strong> the grain filling period, for which there is no reported experimental
evidence at present.
The present study examines the effects <strong>of</strong> <strong>air</strong> <strong>temperature</strong> <strong>and</strong> <strong>light</strong> on the length
<strong>of</strong> the grain filling period, the final grain weight, <strong>and</strong> grain quality <strong>of</strong> one indica (IR20)
<strong>and</strong> one japonica (Fujisaka 5) rice.
MATERIALS AND METHODS
Both IR20 (indica) <strong>and</strong> Fujisaka 5 (japonica) rices were used in all experiments <strong>of</strong>
this study.
Controlled environmentalfacilities. All experiments were conducted in the bioclimatic
laboratory <strong>of</strong> the International Rice Research Institute at Los Banos, Philippines. The
plants were grown in a glasshouse room until 3 days after anthesis, after which they
were transferred to artificially <strong>light</strong>ed cabinets, Koitotron KG-I06 SHL-D cabinets.
The relative humidity <strong>of</strong> the glasshouse room was maintained above 70 percent while
the <strong>temperature</strong> was kept at 29°C between 0900 <strong>and</strong> 1700 hr <strong>and</strong> 21°C during the night.
Daylength was according to the natural conditions.
In the artificially <strong>light</strong>ed cabinets, <strong>light</strong> was provided by 11 X 400 W Toshiba Yoko
lamps DR 400/T <strong>and</strong> 12 x 40 W Mitsubishi white fluorescent lamps. The spectral
composition <strong>of</strong> the radiation is similar in the visible region to that <strong>of</strong> sun<strong>light</strong>. However,
the proportion <strong>of</strong> photosynthetically active radiation is only 25% <strong>of</strong> total short
wave radiation for the artificially <strong>light</strong>ed cabinet compared to about 50 percent for
sun<strong>light</strong>. Photosynthetically active radiation was 114 cal· cm- 2 • day-l at the flag leaf
level unless specified otherwise. Daytime was from 0600 to 1800 hr. The relative
humidity in the artificially <strong>light</strong>ed cabinets was maintained at 70 percent during daytime
<strong>and</strong> 80 percent during the night.
Plant culture. To obtain a large number <strong>of</strong> panicles that would flower simultaneously,
20 pregerminated seeds were sown in a circular pattern in 4-liter plastic pots
(19). Each pot contained 3 kg Maahas clay soil fertilized with 1 g N, 0.5 g P 2
0 6 , <strong>and</strong>
0.5 g KIO.
Sampling <strong>and</strong> measuring procedures. Grain samples were collected from the panicles