Dissection of mechanisms for high yield in two elite rice cultivars

Abstract Understanding mechanisms underlying high yield in elite cultivars and identifying new options to further increase rice yield are major focuses of current rice research. In this work, we develop a general method to tackle the above two challenges using two outstanding indica cultivars, i.e., Huang-Hua-Zhan (HHZ) and Yang-dao 6 (9311), which differ in their strategies to gain high yields. Briefly, HHZ grew slower during seedling stage, whereas accumulated more biomass from tillering to heading stage, and had a shorter leaf photosynthetic functional duration after heading; in contrast, 9311 had stronger seedling vigor, but less biomass accumulation from tillering to heading stage, and longer leaf photosynthetic functional duration after heading. To identify the mechanisms underlying these two different strategies, we dissected factors controlling daily canopy photosynthesis at four different growth stages throughout the growing season using a computational approach. Results showed that higher leaf area index (LAI) due to larger leaf width, regardless of a relatively lower leaf light-saturated photosynthetic rate, contributed to higher canopy photosynthesis and hence stronger seedling vigor of 9311 when LAI was low, whereas these same features decreased canopy photosynthetic rate at young panicle differentiation stage when LAI was high; while instead of increasing canopy photosynthesis to support seedling growth, lower LAI due to smaller leaf width, together with higher leaf light-saturated photosynthetic rate, favored biomass accumulation of HHZ between the late tillering stage and the heading stage. Concurrently, computational simulations revealed that earlier drooping of the panicle of HHZ could increase upper leaves’ light intercept and thus canopy photosynthesis at heading stage by reducing shading from panicles, whereas higher leaf nitrogen content was the most important factor for higher canopy photosynthesis of 9311 during grain filling. Overall, the method presented here can be used to quantitatively identify key factors that limit canopy photosynthetic efficiency of current elite cultivars, which is the basis for crop yield potential, and can be used as targets for rice yield improvement by traditional breeding approaches or by genomic editing technologies.