Indica rice restorer lines with large sink potential exhibit improved nutrient transportation to the panicle, which enhances both yield and nitrogen-use efficiency

The yield and nitrogen use efficiency (NUE) of hybrid rice combinations are closely related to restorer line. Therefore, it is essential to evaluate the agronomic characteristics of restorer lines with high yield and high NUE (HYHN). However, it is unclear which restorer lines are HYHN, and neither have the common agronomic traits of the HYHN restorer lines been identified. Aiming to address this issue, we conducted two filed experiments using three nitrogen applications, which screened five HYHN restorer lines from 15 indica restorer lines. Yield, NUE and nutrient transportation of restorer lines with different yields and NUE types were examined. Yield and total nitrogen absorption in aboveground biomass (TNA) increased, whereas NUE for grain production decreased with increasing nitrogen application levels. The HYHN restorer lines had large spikelets and high weight per panicle that were significantly positively correlated with yield and NUE. Therefore, large sink potential may be beneficial for both yield and NUE. We further studied the differences in nutrient transportation to panicles between the HYHN and low yield and low NUE (LYLN) restorer lines and found that the former had a higher nitrogen absorption level and dry matter weight ratios of panicle in maturity. Moreover, the HYHN lines also had a higher root and neck-panicle node bleeding intensity per stem after heading and more developed vascular bundles of neck-panicle nodes and leaves than the LYLN lines, which could contribute to the transportation of nutrients from root to ground and from stem and leaf to spike. Therefore, the advantages of large sink potential of the HYHN restorer lines include large nutrient accumulation in and distribution to the panicles and smooth flow of nutrients along the transportation channels.