Abstract
In Hokkaido, a leading winter wheat variety, Kitahonami, shows higher yielding ability than a previous variety, Hokushin. To identify the factors determining the high-yielding ability of Kitahonami, we compared its growth and grain yield performance with those of Hokushin in two growing seasons (2011-12 and 2012-13). The grain yield of Kitahonami was 8% greater than that of Hokushin. This difference was due to a higher number of grains per ear and 1000-grain weight. The high-yielding ability of Kitahonami was attributed to the large sink capacity. At maturity, the total dry weight of Kitahonami was 13% heavier than that of Hokushin. This increased total dry weight was a result of the increased crop growth rate (CGR) from the milk-ripe to maturity stage. In particular, the dry weight of the ear was greatly increased. A strong source activity during the later grain filling phase also contributed to the high-yielding ability of Kitahonami. The nitrogen content of the second and third leaves at the milk-ripe and maturity stages was higher in Kitahonami than in Hokushin. The erect green leaves of Kitahonami probably absorbed radiation more effectively than those of Hokushin, leading to a higher net assimilation rate (NAR) in the later grain filling phase and higher dry-matter production after the milk-ripe stage.
