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

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102 S. YOSHIDA <strong>and</strong> T. HARA Downloaded by [Universitaetsbibliothek Giessen] at 15:43 06 April 2015 results were obtained for both IR20 <strong>and</strong> Fujisaka 5 at two <strong>temperature</strong>s, hence the data are presented for only IR20 at a daily mean <strong>temperature</strong> <strong>of</strong> 28°C (Fig. 6). Low <strong>light</strong> intensity consistently decreased grain weight to a small extent on all the branches. On the other h<strong>and</strong>, low <strong>light</strong> intensity decreased the percentage <strong>of</strong> filled grains markedly on the lower branches <strong>of</strong> the panicle. These effects <strong>of</strong><strong>light</strong> intensity on grain fIlling are in good agreement with our previous findings that low <strong>light</strong> intensity during ripening period affects grain yield through decreasing the percentage <strong>of</strong> fIlled grains but it has little effect on grain weight (29). Grain weight <strong>and</strong> percentage oj filled grains. Since <strong>light</strong> affects both grain weight (W) <strong>and</strong> percent fllled grains (F), the overall effect <strong>of</strong> the <strong>light</strong>-<strong>temperature</strong> interaction on grain yield can be best assessed by computing W X F, i.e., ripening grade. The combi. Xl 1 .s:: g 2 as li 3 ~4 E '~ 5 '0 6 Grain weight (mg) Filled grains (%) Grain number o 13 14 15 16 17 0 50 60 7080 90100 O'{-_-i5~_.!.Ir-0_--=-15;; .... 5 7 'in 8 ~ 9'---0----' 1 2 3 1 . 2· 3 4 5 6 7 8 9~~--.......... --.......... ~ Fig, 6. Effect <strong>of</strong> <strong>light</strong> on grain filling <strong>of</strong>IR20 riee at 32/24·0. (Low <strong>light</strong>-36 cal. em-" day-I; high <strong>light</strong>=1l4cal. cm-·. day-I PAR.) (PAR: Photosynthetically active radiation). Table 4. Effect <strong>of</strong> <strong>light</strong> <strong>and</strong> <strong>temperature</strong> on grain growth <strong>of</strong> IR20 <strong>and</strong> Fujisaka 5 rices. Grain Filled Ripening Lightll Temperatures, weight (W)I' grains (F) grade (mg) (%) (WxF) IR20 Low Low 15.5 65 1014 ( 71)11 Low High 14.8 62 9)0 ( 64) High Low 16.3 87 1423 (100) High High 16.0 85 1370 ( 96) Fujisaka 5 Low Low 22.0 86 1890 ( 90) Low High 2M 84 1718 ( 82) High Low 23.0 91 2102 (100) High High 21.9 92 2013 ( 96) 1) Low: 36cal. em-I. day-l PAR (photosynthetically active radiation), High: 114cal. cm-•• day-' PAR. II Low: 23/15°0, High: 32/24°0. I' LSD value at 5% level is 0.2 for both varieties. "Figures in parenthesis indicate relative values with 100 serving as the maximum.
Temperature <strong>and</strong> Light on Rice Grain Filling 103 nation <strong>of</strong> high <strong>light</strong> intensity <strong>and</strong> a low <strong>temperature</strong> gave the maximum ripening grade for both rice varieties (Table 4). Taking the maximum value as 100 for each variety, the ripening grade was reduced by 36 percent in IR20 <strong>and</strong> 18 percent in Fujisaka 5 when the <strong>light</strong> intensity was low <strong>and</strong> the <strong>temperature</strong> was high. Apparently, grain filling, <strong>and</strong> hence, the yield <strong>of</strong> IR20 is more likely to be reduced by adverse climatic environments than are those <strong>of</strong> Fujisaka 5 rice. DISCUSSION Downloaded by [Universitaetsbibliothek Giessen] at 15:43 06 April 2015 The length <strong>of</strong> the grain filling period markedly affects the yield <strong>of</strong> rice because it affects the maximum amount <strong>of</strong> solar energy available for grain filling. Additionally, it constitutes the last part <strong>of</strong> the rice plant's life cycle; this knowledge about the grain filling period can contribute to the overall <strong>und</strong>erst<strong>and</strong>ing <strong>of</strong> the total growth duration <strong>of</strong> rice varieties. Existing information on the effect <strong>of</strong> environmental factors <strong>and</strong> (or) plant physiological factors on the length <strong>of</strong> the grain filling period <strong>of</strong> rice is scarce. An.n et al. (1) reported that while the grain filling <strong>of</strong> a japonica rice was completed in about 25 days after anthesis at a daily mean <strong>temperature</strong> <strong>of</strong> 25°C, it took much longer when the daily mean <strong>temperature</strong> was 21 °C, <strong>and</strong> was not complete even after 75 days from anthesis when the daily mean <strong>temperature</strong> was 17°C. Their experiment was conducted in <strong>temperature</strong>-controlled glasshouse rooms where day <strong>and</strong> night <strong>temperature</strong>s were held constant. NAGATO <strong>and</strong> EBATA (11, 12) also measured the rate <strong>of</strong> grain filling <strong>und</strong>er different <strong>temperature</strong> regimes. When YAMAKAWA (24) planted 12 rice varieties in the field in Japan at different times so that these rice crops would be exposed to different daily mean <strong>temperature</strong>s during the ripening period, he showed that japonica rice ripened over 30 days when the daily mean <strong>temperature</strong> was about 29°C, while ripening took 53 days when the daily mean <strong>temperature</strong> was 18°e. The time for maturity was determined by visual examination in this experiment. In the present study, rice grains were fo<strong>und</strong> to mature faster than was expected, only 13 days were required for the upper grains <strong>of</strong> IR20 rice to reach the maximum weight when the daily mean <strong>temperature</strong> was 28°C, <strong>and</strong> 18 days for Fujisaka 5 rice. When the daily mean <strong>temperature</strong> was lower, 16°C, the upper grains <strong>of</strong> IR20 rice achieved maximum weight in 33 days, whereas those <strong>of</strong> Fujisaka 5 rice required 43 days. The critical low <strong>temperature</strong> for photosynthesis has been reported as IS.5°C for japonica rice (23) <strong>and</strong> between 20° <strong>and</strong> 25°e for indica rice (14). In the experiment <strong>of</strong> Aimi et al., the day <strong>and</strong> night <strong>temperature</strong>s were both 17°0 which is a subnormal <strong>temperature</strong> for photosynthesis <strong>of</strong> japonica rice, In our experiment, however, at a daily mean <strong>temperature</strong> <strong>of</strong> 16°0, the day <strong>temperature</strong> was held at 20°C, which is above the critical low <strong>temperature</strong> for photosynthesis <strong>of</strong> japonica rice. This difference in the <strong>temperature</strong> regimes may explain the variation in the results obtained in the present study <strong>and</strong> those <strong>of</strong> Aimi et aI, It is normally assumed that <strong>light</strong> intensity has little or no effect on the length <strong>of</strong> the
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Yoshida und Hara - 1977 - Effects of air temperature and light on grain fill

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