Comparison of yielding ability, yield component and harvest index in new rice varieties bred for cold climate regions

摘要

To clarify the high yielding characteristics of new rice varieties recently bred in the cold region of Japan, data were recorded on their yielding ability, yield components and harvest index in 1996 (24 varieties) and 1997 (21 varieties), and compared with those of 4 popular varieties registered after 1970 in Tohoku region. The grain yield was 716-845 g/m2 in 1996 and 696-799 g/m2 in 1997, and the difference among the rice varieties was 100-130 g/m2 in both years. Twenty of the new rice varieties recorded over 750 g/m2 grain yield in 1996 and 15 varieties recorded a similarly high yield in 1997. Compared with popular varieties, the new rice varieties were classified into 4 groups: (1) varieties having a larger sink due to a larger number of spikelets per m2, including Ouu 316 and Ouu 339; (2) varieties having a larger sink due to a heavier grain weight and similar number of spikelets per m2, including Fukuhibiki, Akita 59 and Manamusume; (3) varieties having a similar sink size due to a heavier grain weight but smaller number of spikelets per m2, including Okiniiri and Iwanan 6; and (4) varieties having a similar sink showing a similar number of spikelets per m2 and similar grain weight, including Hananomai and Jyoudeki. These results suggest that in order to breed high yielding rice varieties in the cold region of Japan, the sink capacity must be enlarged by either increasing the number of spikelets per m2 or increasing the grain weight, maintaining a similar number of spikelets per m2.