Nitrogen Uptake and Remobilization from Pre- and Post-Anthesis Stages Contributes Towards Grain Yield and Protein Concentration in Wheat Nam Rils Grown in Limited Nitrogen Condition

Nitrogen (N) remobilization from vegetative tissue to developing grains in wheat depends on environmental and genetic factors. We assessed genetic variation for accumulation, partitioning, and remobilization of N towards grain, and its association with grain protein concentration (GPC) and yield in a nested association mapping (NAM) RILs (195 lines). These lines were derived by crossing Paragon (P) with CIMMYT core germplasm (P×Cim), Baj (P×Baj), Watkins (P×Wat), and Wyalkatchem (P×Wya) and were grown under field conditions with limited N supply in northern India. A genotype-dependent positive association of grain yield with pre- and post-anthesis biomass accumulation was observed. Among four groups, the P×Cim lines performed superior, while the P×Wya lines responded poorly under low N input. The N-remobilization efficiency (NRE) was correlated with aboveground N accumulation at anthesis (AGN A ) and grain yield but negatively associated with AGN at post-anthesis (AGN PA ) suggesting higher N uptake to anthesis would favour higher N remobilization towards grain filling. Hierarchical cluster analysis based on NRE and grain yield revealed four clusters of RILs defined as efficient (31), moderately efficient (59), moderately inefficient (58), and inefficient (47). In the N-efficient lines, AGN A contributed to 77% of total N accumulated in grains, whilst in the N-inefficient lines, it was 63%. Among the four clusters, 16 lines of P×Cim, 10 from P×Wat, and 5 from P×Baj were categorized as N efficient while most of the P×Wya lines were inefficient or moderately inefficient. Several N efficient lines exhibited positive grain protein deviation (GPD), combining high grain yield and GPC and this is the first report of genotype-dependent GPD associated with both AGN PA and AGN A in wheat. These positive GPD lines could be deployed as varieties or serve as genetic resource for improving grain yield with high GPC under limited N condition. We propose that traits favouring pre- or post-anthesis biomass accumulation and N uptake may be targeted for breeding to improve grain-yield and protein concentration under limited N.