Varietal Differences in Morphological Traits, Dry Matter Production and Yield of High-Yielding Rice in the Tohoku Region of Japan

A two-year field experiment was conducted with japonica type high-yielding variety "Fukuhibiki," indica type high-yielding variety "Takanari," large grain type high-yielding variety "Bekoaoba" and conventional japonica type varieties "Akitakomachi" and "Hitomebore" in the Tohoku region (colder area of Japan). The panicles of Takanari and Bekoaoba located lower in the canopy, and the flag leaf of those varieties intercept more solar radiation, because the flag leaf was long and the first internode of panicle did not emerge above the lamina joint of the flag leaf in Takanari and the panicle hung lower in Bekoaoba. The three high-yielding varieties produced a large sink size, due to the large potential sink size in Takanari, the very large grain size in Bekoaoba and the rather large number of spikelets per panicle and somewhat large grain size in Fukuhibiki. Based on dry matter production, the three high-yielding varieties had a high harvest index, although there were little varietal differences in top dry weight at maturity. Unhulled rice weight of the three high-yielding varieties was heavier than that of other varieties at 30 days after heading (30 DAH). However, there were no varietal differences in the increase in unhulled rice weight from 30 DAH to maturity (later than 50 DAH), probably due to the continual growth of the grains located lower until the late ripening period in all varieties. In conclusion, the traits related to high yield varied greatly among varieties. However, the three high-yielding varieties had a large sink size, heavy unhulled rice weight at 30 DAH and high harvest index.