Tiller fertility is critical for improving grain yield, photosynthesis, and nitrogen efficiency in wheat

Genetic improvement has promoted grain yield and nitrogen use efficiency (NUE) of wheat during the past decades, therefore, grain yield and NUE of wheat cultivars were high as compared to previous cultivars in the Yangtze River Basin since the 2000s. However, the critical traits and mechanisms of higher grain yield and NUE are not known. To explore the higher grain yield and NUE mechanisms of these new cultivars, 21 local cultivars were cultivated for three growing seasons from 2016 to 2019. Significantly positive correlations were observed between grain yield and NUE in the three years. The cultivars were grouped into high, medium, and low grain yield and NUE groups (abbreviated to HH, MM, and LL, respectively). Significantly high grain yield and NUE were observed in the HH group. High grain yield was attributed to more effective ears by high tiller fertility and greater single-spike yield by increasing post-anthesis single-stem biomass. Compared to other groups, longer leaf stay-green ability and greater flag leaf photosynthetic rate after anthesis were detected in HH group. It also showed higher N accumulation at pre-anthesis which contributed to increasing N accumulation per stem, including stem and leaf sheath, leaf blade, and unit leaf area at pre-anthesis, and promoting N uptake efficiency, the main contribution of high NUE. Moreover, Tiller fertility was positively related to N accumulation per stem, N accumulation per unit leaf area, leaf stay-green ability, and flag leaf photosynthetic rate, indicating that improving tiller fertility promoted N uptake, leaf N accumulation, and photosynthetic ability, thereby achieving synchronous improvements in grain yield and NUE. Therefore, tiller fertility is proposed as an important kernel indicator that can be used in the breeding and management of cultivars to improve agricultural efficiency and sustainability.