Analysis of high yielding mechanism of rice varieties belonging to different plant types .1. Comparison of growth and yield characteristics and dry matter production

To clarify the high yielding characteristics of new rice varieties bred recently in the Tohoku region of Japan, their growth and yield characteristics and dry matter production were examined in 1994 and 1995, as compared with those of Hitomebore and Kiyonishiki, popular cultivars in the region. The grain yields of the cultivars and strains used were in a relatively high level, ranging from 650 to 815 g m(-2). The sequence of grain yield was Fukuhibiki> Ouu 316, Kiyonishiki> Ouu 327 > Hitomebore. High grain yields in Fukuhibiki and Ouu 316 of the panicle weight type with short culm were mainly due to the large number of spikelets m(-2), which was mainly determined by the large number of spikelets per panicle. Fukuhibiki was also characterized by a large grain weight and a high percentage of ripened grains. The percentage of ripened grains was mainly governed by the ripened grains on the secondary rachis branch, which closely related to sink size. The high percentage of ripened grains of Fukuhibiki was due to the high percentage of ripened 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 ripened grains and markedly large grain weight, although this strain had a small number of panicles and spikelets m(-2). As compared with Hitomebore, Fukuhibiki and Ouu 316 with low plant length showed large weights of total dry matter and extremely large weights of dry panicles, which contributed to their large harvest indices. The results suggest that high yielding Fukuhibiki and Ouu 316 possess the excellent characteristics of dry matter production and distribution.