Yoshida - 1981 - Fundamentals of Rice Crop Science

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RICE PLANT CHARACTERS IN RELATION TO YIELDING ABILITY 229 Table 6.7. Benefits and disadvantages of contrasting plant characteristics. a Plant Part Characteristics Benefits and disadvantages Leaf Thick Thin Higher photosynthetic rate per unit leaf area. Associated with development of larger LAI. Associated with more erect habit. Short and small Associated with more erect habit. Even distribution of leaves in a canopy. Erect Uses solar energy efficiently Droopy when LAI is large. Uses solar energy efficiently when LAI is small. Suppresses weeds. Culm Short and stiff Prevents lodging. Tall Suppresses weeds. Tiller Upright (compact) High tillering Permits greater penetration of incident light into a canopy. Adapted to a wide range of spacings; capable of compensating for missing hills; permits faster leaf area development. Low tillering Can be used for direct seeding. Root Shallow and low Uses high proportion of assimilates root/shoot ratio for shoot. Deep and high Increases resistance to drought. root/shoot ratio Uses soil nitrogen and recovers applied nitrogen efficiently. Panicle Low sterility at high Permits use of larger amount of nitrogen rates nitrogen. High harvest index Associated with high yields. Small grain Related to fast grain filling. Growth Large grain Early maturing Has potential for high yields (?). Increases grain production per day. duration Increases water use efficiency. Requires close spacings to achieve high yields. Late maturing Adapted to low fertility (?) Photoperiod Sensitive Adapted to areas of a long monsoon sensitivity season. Insensitive Can be grown any time of a year; fitted to multiple cropping systems. Early Fast Suppresses weeds. growth Slow Essential for early maturing varieties. Prevents excessive growth at later stages under a good management. a Adapted from Yoshida (1972, 1977b, 1978) and Yoshida et al (1972). Thus, an intermediate plant height has some advantages where there is undependable water control but that benefit may not be realized without more lodging resistance.
230 FUNDAMENTALS OF RICE CROP SCIENCE 6.7.2. Leaf angle Crop photosynthesis models indicate that droopy leaves are slightly better than erect leaves when the LAI is less than 3. And the leaf inclination is not too important when the LAI is less than 4 (Duncan 1971, Monteith 1965, van Keulen 1976). A LAI of 4 at heading is sufficient to produce about 5 t/ha in both the wet and dry seasons (see Fig. 6.4). In other words, the leaf angle per se is not important when grain yield is less than 5 t/ha. 6.7.3. Tillering capacity High tillering capacity basically relates to the plant’s ability to make maximum use of space. High tillering is considered more important under subnormal conditions than under optimal conditions. 6.7.4. Benefits and disadvantages of contrasting plant characteristics Each plant character has benefits and disadvantages under different conditions. Under a good environment and with good management, IR8 and similar semidwarf varieties are ideal. On the other hand. under diverse environments and different management levels, the problem becomes location and management specific. There is no single variety that can meet all the requirements set by the different environment and management levels. Apparently, gains in one aspect are accompanied by losses in another. In such a situation, it is important for plant breeders to recognize the benefits and disadvantages of contrasting plant characteristics (Table 6.7).
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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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