Agronomic and physiological performance of indica/japonica hybrid rice cultivar under low nitrogen conditions

Abstract

It is generally believed that indica/japonica hybrid rice (IJHR) cultivars have a higher yield potential under high nitrogen (N) supply, but it is not established whether IJHR could obtain a relatively high yield under low N conditions. In order to fill this gap of knowledge, six rice cultivars were examined in this study, consisting of three IJHR cultivars and three japonica hybrid rice (JHR) cultivars, all of which are prevalent in the lower Yangtze River plain. These cultivars were compared for grain yield and other closely-related agronomic and physiological traits under two N input treatments: one being a low application of N (LN) and the other a normal application of N (NN), in 2016 and 2017 in Hangzhou, Zhejiang Province, China. Compared to JHR, IJHR showed grain yield increases of 15% under NN and 25% under LN. Relative to JHR, there are four main agronomic and physiological traits which are associated with IJHR’s superior yield performance under LN conditions. Firstly, IJHR has less redundant vegetative growth, evidenced by a higher percentage of productive tillers. Secondly, IJHR has the larger sink size, resulting from higher spikelet numbers per panicle and sufficient panicles per m2. Thirdly, IJHR exhibited increased shoot activity during the grain filling period, indicated by an increased accumulation of non-structural carbohydrate (NSC) in the stems at heading time, a higher percentage of NSC remobilization from stem to grains during the ripening period, higher enzyme activity in the grains’ sucrose-to-starch conversion process, and greater photosynthesis production during the ripening period. Finally, IJHR was seen to have improved root morpho-physiological traits, characterized by greater root biomass, deeper soil distribution at heading time, and higher root oxidation activity (ROA) during the ripening period. Our results suggest that IJHR’s improved agronomic and physiological traits will lead to improved yields under low N input conditions.