Yoshida - 1981 - Fundamentals of Rice Crop Science

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RICE PLANT CHARACTERS IN RELATION TO YIELDING ABlLlTY 217 The plant-type concept has since attracted considerable attention and more intensive examination in Japan (Murata 1961, Hayashi and Ito 1962, Hayashi 1968, 1969). Experimental data for tropical varieties clearly demonstrate that certain morphological characters are indeed associated with yielding ability (Tanaka et al 1964, 1966a). Work on plant type has been well summarized and the concept appears to have been widely accepted by rice breeders in many countries as a guide for breeding high yielding varieties (Ishizuka 1971, Jennings 1964, Yoshida 1972). The following morphological characters deserve particular attention: • Short, stiff culms. • Erect leaves. • High tillering. 6.3.2. Short, stiff culms The increased resistance of improved varieties to lodging appears to be the single character most responsible for high yields. A short, stiff culm makes the rice plant more lodging resistant. Table 6.2 compares the yield performance of Peta, a tall, lodging-susceptible variety, with that of IR8. The mechanical support alone increased the grain yield of Peta by 60% in the wet season and by 88% in the dry. Although height is the most important plant character associated with lodging, a short variety is not always lodging resistant. There are differences in the stiffness of short culms (Chandler 1969). The importance of lodging resistance has long been recognized, but only in recent years has the semidwarf gene been effectively introduced into tropical rice varieties. In southern Japan, Hoyoku and its sister high yielding varieties are largely characterized by increased lodging resistance (Shigemura 1966). 6.3.3. Erect leaves Erect leaves allow the deeper penetration and more even distribution of light, which results in increased crop photosynthesis (see Chapter 5). In one model, the crop photosynthesis of an erect-leaved canopy is about 20% higher than that of the droopy-leaved canopy when the LAI is extremely high (van Table 6.2. An example of the yield performance of IR8 and Peta in the wet and dry seaons. a Yield (t/ha) Variety Wet Dry Mean season b season c Peta, not supported 2.83 (100) 3.97 (100) 3.40 (100) Peta, supported 4.52 (160) 7.46 (188) 5.99 (176) IR8. not supported 6.10 (216) 9.10 (229) 7.60 (224) a Yoshida, et al (1972). b 1966, 30– x 30-cm, spacing, 100 kg N/ha. c 1968, 20- x 20-cm spacing, 120 kg N/ha.
218 FUNDAMENTALS OF RICE CROP SCIENCE 6.2. Difference in light-photosynthesis curves between rice populations with erect and droopy leaves (Tanaka et al 1969). Keulen 1976). This model assumes that all the leaves are uniformly oriented at angles of 0° or 90° with respect to the horizontal plane. When we consider leaf angles and the fight environment of individual leaves within a canopy, almost intuitively we visualize that a combination of short, erect upper leaves grading to droopy, longer lower leaves is ideal for maximum crop photosynthesis. In fact, theory and experimental evidence shows that this plant architecture leads to the maximization of incident solar radiation (Matsushima et al 1964a, Duncan 1971). There is only one rice experiment indicating that the droopy-leaved canopy has a lower crop photosynthesis than the erect-leaved canopy at high light intensities (Fig. 6.2); accordingly, the droopy-leaved canopy was lower than the erect-leaved 6.3. Response of high-tillering (IR8) and low-tillering (IR154-45-1) varieties to spacing (adapted from Yoshida and Parao 1972).
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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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Yoshida - 1981 - Fundamentals of Rice Crop Science

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