Improvements in grain yield and nutrient utilization efficiency of japonica inbred rice released since the 1980s in eastern China

The cropping area of japonica inbred rice has expanded rapidly since the 1980 s, which occupies 90% of the total cropping area nowadays in Jiangsu, east China. In this process, information on the genetic improvement in grain yield and nutrient use efficiency of japonica inbred rice is still limited. Fifteen japonica inbred rice released from 1983 to 2014 were tested during the 2018 and 2019 rice-growing seasons. Grain yield increased yearly at 65.1 kg ha⁻¹ (0.65%) in 2018 and 58.1 kg ha⁻¹ (0.59%) in 2019. Panicles per m² and filled-kernel percentage decreased (P < 0.01), while spikelets per panicle increased (P < 0.01), with year of release. Pre-heading biomass, post-heading biomass, and total biomass increased (P < 0.01 or P < 0.05) linearly with year of release; while harvest index gradually increased with year of release before 2000, thereafter remaining relatively stable. Leaf area index (LAI) at heading and maturity, plant height, specific leaf weight, and flag leaf photosynthetic rate at heading, and intercepted radiation and radiation use efficiency (RUE) from heading to maturity all increased (P < 0.01) with year of release, which was associated with the increased biomass accumulation during the breeding process. Genetic improvement has increased total N, P, and K accumulation, as well as their use efficiencies. Grain yield and harvest index correlated positively (P < 0.01) with NUEg, PUEg, and KUEg among rice cultivars. Our results suggested the impressive progress in grain yield and nutrient use efficiency of japonica inbred rice since the 1980 s in eastern China. The yield progress was mainly attributed to the increased spikelets per panicle. For rice cultivars released before 2000, an increase in harvest index contributed more to yield improvement than total biomass; while the yield improvement after 2000 resulted from total biomass. The results also indicated possible opportunities for improving use efficiency of N, P, and K through increasing harvest index in rice.