Higher light utilization and assimilate translocation efficiency produced greater grain yield in super hybrid rice

Background The yield potential of super hybrid rice has been increased by nearly 10% compared to ordinary hybrid or inbred rice. To further explain the reasons for the yield advantage of hybrids, we conducted investigations into the underlying physiological mechanism by considering leaf photosynthesis in combination with assimilate translocation. Methods Field experiments were conducted from 2020 to 2021 to compare the yield, photosynthetic performance, and efficiency of assimilate translocation-related traits between super hybrid rice (Yliangyou5867 and Yliangyou3218) and inbred super rice (Zhendao11 and Nanjing9108) under two nitrogen (N) levels. Results The average yield of hybrids across N levels was respectively 15.7% and 25.3% higher than that of inbreds in 2020 and 2021. Before heading, the biomass of hybrids was significantly higher than that of inbreds, and hybrids exhibited a higher harvest index. The higher radiation use efficiency (RUE) in hybrids was primarily due to an improved photosynthetic rate ( P n ). Dry matter translocation from stem and leaf to panicle of hybrids was higher than that of inbreds. The hybrids also exhibited greater fluctuation in day-night sugar content and higher phloem sugar content which indicated higher assimilate translocation efficiency with hybrids. Conclusions Our results revealed that the higher RUE was responsible for the higher aboveground biomass before heading in hybrids. Furthermore, the improved biomass partitioning and remobilization, as demonstrated by an increase in assimilate translocation efficiency, contributed to higher harvest index and grain yield in hybrids. Crop breeders should focus on coordinating light utilization and assimilate translocation efficiency in super hybrid rice.