ANALYSIS OF HIGH-YIELDING MECHANISM OF RICE VARIETIES BELONGING TO DIFFERENT PLANT TYPES .1. COMPARISON OF GROWTH AND YIELD CHARACTERISTICSAND DRY-MATTER PRODUCTION

To clarify the high yielding characteristics of new rice varieties bre d recently in the Tohoku region of Japan, their growth and yield chara cteristics and dry matter production were examined in 1994 and 1995, a s compared with those of Hitomebore and Kiyonishiki, popular cultivars in the region. The grain yields of the cultivars and strains used wer e in a relatively high level, ranging from 650 to 815 g m(-2). The seq uence of grain yield was Fukuhibiki> Ouu 316, Kiyonishiki> Ouu 327 > H itomebore. High grain yields in Fukuhibiki and Ouu 316 of the panicle weight type with short culm were mainly due to the large number of spi kelets m(-2), which was mainly determined by the large number of spike lets per panicle. Fukuhibiki was also characterized by a large grain w eight and a high percentage of ripened grains. The percentage of ripen ed grains was mainly governed by the ripened grains on the secondary r achis branch, which closely related to sink size. The high percentage of ripened grains of Fukuhibiki was due to the high percentage of ripe ned grains on the secondary rachis branch. The grain yield in Ouu 327 of the big grain type was mainly due to a fairly high percentage of ri pened grains and markedly large grain weight, although this strain had a small number of panicles and spikelets m(-2). As compared with Hito mebore, Fukuhibiki and Ouu 316 with low plant length showed large weig hts of total dry matter and extremely large weights of dry panicles, w hich contributed to their large harvest indices. The results suggest t hat high yielding Fukuhibiki and Ouu 316 possess the excellent charact eristics of dry matter production and distribution.