LAUSR

ABSTRACT Hokkaido is a major wheat production region in Japan and is located in the northernmost area of the country. The winter wheat variety ‘Kitahonami’ is the most extensively grown variety in Hokkaido. We established a novel cultivation method to achieve stable high yields of ‘Kitahonami’ following examination of the morphological aspects of wheat cultivated in Hokkaido, Japan. The leaves of ‘Kitahonami’ are highly erect and potentially absorb radiation more effectively than those of ‘Hokushin’, which is the previous variety grown in Hokkaido, leading to a higher net assimilation rate in the later grain-filling phase and higher dry matter production after the milk-ripe stage; thus, we consider ‘Kitahonami’ as an ideotype. Furthermore, tracking tillering has been attempted using commercially available colored rubber bands. In winter wheat varieties including ‘Kitahonami’ in Hokkaido, the productive capacity of the tillers with >2 leaves before winter is high, leading to increased grain number and heavy spike weight. A decrease in the sowing rate is critical for stable high yields of ‘Kitahonami’. We have developed a novel nitrogen topdressing method that considers the plant type and tillering of ‘Kitahonami’. When the nitrogen topdressing is applied at the spike formation stage, maintaining a higher net assimilation rate until later phases of grain filling is possible using improved plant types with erect leaves. This paper summarizes the novel techniques for improving grain yield performance based on findings of the tillering trends and a plant type of ‘Kitahonami’. Graphical Abstract