Abstract
The high-yielding winter wheat variety ‘Kitahonami’ is the most widely cultivated variety in Hokkaido, Japan, accounting for more than 50% of the country’s domestic wheat production. In this study, we studied the factors underlying the high-yielding ability of ‘Kitahonami’ based on ripening physiology. ‘Kitahonami’ and an older variety ‘Hokushin’, were cultivated in 2014/2015 and 2015/2016; and, the dry matter weight and nitrogen accumulation in each organ and site were examined throughout the ripening period. In 2014/2015, the grain yield was significantly higher in ‘Kitahonami’ than in ‘Hokushin’, owing to the higher number of grains per unit area in the former. Although the number of grains on each ear in ‘Kitahonami’ was lower, the higher grain weight resulted in a higher yield in 2015/2016. The total dry weight increased linearly from heading to maturity in ‘Kitahonami’ while it increased significantly around the milk-ripe stage in ‘Hokushin’, tapering off thereafter. Therefore, in ‘Kitahonami’, the crop growth rate (CGR) was lower in the first half of the ripening period and higher in the second half than in ‘Hokushin’. ‘Kitahonami’, had a low grain nitrogen concentration in the second half of the ripening period, which led to a low grain nitrogen content in 2014/2015. The varietal characteristics leading to low grain protein content were clarified based on nitrogen metabolism during the ripening period.
