ANALYSIS OF THE DRY-MATTER PRODUCTION PRO CESS AND YIELD FORMATION OFTHE HIGH-YIELDING RICE CULTIVAR TAKANARI FROM 1991 TO 1994

To clarify the physiological and ecological characteristics directly r esponsible for high yields in rice plants, the yield and yield compone nts, the process of dry matter production and the light-intercepting c haracteristics were compared between the cultivar Takanari, a high-yie lding variety bred in 1990, and the cultivar Nipponbare, a standard Ja panese variety. The Takanari yield of 528 similar to 642 kg/10 a was a bout 100 kg/10 a higher than the yields for Nipponbare in 1991 and 199 3, poor harvest years. The Takanari yield of 817 similar to 888 kg/10 a was about 230 kg/10 a higher in 1992 and 1994, good harvest years, o wing to higher dry matter productivity and harvest index for Takanari. In spite of a great number of spikelets per square-meter for Takanari , due to the large number of spikelets per panicle with more secondary rachis-branches, the percentages of ripened grains were almost the sa me as those of Nipponbare. Crop growth rates were higher owing to the higher net assimilation rate after heading in 1991, and owing to both higher net assimilation rate and larger mean leaf area index after the maximum tiller number stage in 1994. The net assimilation rate for Ta kanari was higher due to better light-intercepting characteristics con sidering the arrangement of leaves and position of panicles in the can opy. The higher harvest index for Takanari mainly resulted from a high er amount of assimilates translocated to the panicle from the culm and leaf sheath after heading.