Yoshida - 1981 - Fundamentals of Rice Crop Science

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58 FUNDAMENTALS OF RICE CROP SCIENCE O. glaberrimas flowered but less than 5% in O. sativa had anthesis (IR lines and Speed 70). Pollen tubes start elongating after germination. Fertilization is normally completed 5–6 hours after anthesis; then the fertilized ovary develops into brown rice. 1.1.1. RIPENING 1.11.1. Ripening and senescence The ripening period is characterized by grain growth — increase in size and weight, changes in grain color, and senescence of leaves. At the early stages of ripening, the grains are green; they turn yellow as they mature. The texture of the grains changes from a milky, semifluid state to a hard solid. On the basis of such changes the ripening period is subdivided into milky, dough, yellow ripe, and maturity stages. Before heading, a considerable amount of starch and sugar accumulates in the culms and leaf sheaths. This accumulated carbohydrate is translocated to the grains during ripening. Leaf senescence starts from the lower leaves and extends upward as the plant matures. Leaf senescence is faster in indica than in japonica rices and in warm regions than in cool regions. In cool regions, some leaves remain green even at maturity. The relationship between rate of leaf senescence and grain filling is complex. In some cases, faster leaf senescence results from a faster translocation of carbohydrates and proteins from leaves to grains, which in turn may be related to faster grain filling. In other cases, faster leaf senescence indicates unfavorable weather or soil conditions. 1.11.2. Growth of single grains The process of grain growth is quantified by the increase in dry weight and the 1.48. Growth of single grains IR20 and Fujisaka 5 at different temperatures (Yoshida and Hara 1977).
GROWTH AND DEVELOPMENT OF THE RICE PLANT 59 1.49. Changes in the water content at successive stages of growth of 2 varieties of rice under 3 temperature regimes (Yoshida and Hara 1977). decrease in water content. The rate of grain growth is faster and the grain filling period is shorter at higher temperatures (Fig. 1.48). The duration of grain filling, defined as the number of days required to reach maximum weight, is 13 days at a mean temperature of 28°C, and 33 days at 16°C for IR20, an indica rice. Fujisaka 5, a japonica rice, takes a little longer to ripen: 18 days at a mean temperature of 28°C and 43 days at 16°C. Comparable figures for a field crop are much greater than those for a single grain because time of heading and anthesis vary among panicles and among spikelets within the same panicle. Hence, the crop, as a whole, takes a longer time to ripen than does a single grain. The final grain weights attained at high and low temperatures are about the same for IR20, suggesting that IR20 is well adapted to high temperatures during ripening. In Fujisaka 5, however, the final grain weight at 28°C is about 15% less than that at 16°C. Thus, high temperatures appear to have some detrimental effect on Fujisaka 5. Their detrimental effect is much more conspicuous in wheat (Sofield et al 1974). During the initial phases of grain filling, the water content of the grains is about 58% and it declines to about 20% or less at maturity (Fig. 1.49). As temperatures increase, water content decreases faster. 1.11.3. Grain growth of a field crop Grain growth of a field crop is initially slow, enters a linear phase where the growth rate is fast, and then slows down toward maturity (Fig. 1.50). Agronomically, the duration of ripening is from the date of heading to the time when the maximum grain weight is attained. The time of harvest is usually determined by past experience, grain color, and leaf senescence. The length of ripening, predominantly affected by temperature, ranges from about 30 days in the tropics to 65 days in cool temperate regions such as Hokkaido, Japan, and New South Wales, Australia (Tanaka and Vergara 1967). In crop physiology, the effective grain-filling period (T) or the period of physiological maturity is defined as shown in Figure 1.50. The length of T is considered more meaningful for grain growth than the length of the agronomic
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FOREWORD Rice is vital to more than
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CONTENTS Foreword Preface GROWTH AN
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3.2. Adaptation to Submerged Soils
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4.5. Corrective Measures for Nutrit
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1 .1. OUTLINE OF THE LIFE HISTORY T
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GROWTH AND DEVELOPMENT OF THE RICE
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GROWTH AND DEVELOPMENT OF THE RICE
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5.1. PHOTOSYNTHESIS 5.1.1. Photosyn
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PHOTOSYNTHESIS AND RESPIRATION 197
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Photosynthetic characteristics Meas
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A traditional tall variety vs an im
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Table 7.6. An example of high yield
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REFERENCES AGRICULTURAL POLICY STUD
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Yoshida - 1981 - Fundamentals of Rice Crop Science

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