Genetic analysis of maize grain yield components and physiological determinants under contrasting nitrogen availability

Context Most maize breeding is conducted under high-input conditions, with nitrogen supply being crucial due to its impact on yield. Aims This study aimed to investigate broad-sense heritability, and general and specific combining ability variances of physiological traits defining grain yield under contrasting soil nitrogen supply. Methods A six-parent full diallel cross was analysed under high (fertilised with 200 kg N/ha) and low (unfertilised control) nitrogen supply in two seasons. We measured kernel number per plant and kernel weight, the associated traits of plant growth during the critical and grain-filling periods, and source–sink relationships in both periods. Key results Heritabilities of traits ranged from 0.54 to 0.88, and general surpassed specific combining ability for most traits. At low nitrogen (1) the relative importance of general combining ability estimated by Baker’s ratio increased across traits (low nitrogen: 0.90 vs high: 0.85) because the decrease in combining ability variance was larger for specific than general (–78% vs −39%), and (2) source–sink relationship during grain filling had the highest Baker’s ratio (0.96) and heritability (0.78). Plant growth rates during the critical period and kernel number increased substantially at high nitrogen (40 and 34%, respectively), and they had the highest heritability (0.79 and 0.88) and Baker’s ratio (>0.90). Conclusions Low nitrogen environments increased the relative importance of general combining ability effects, and high yield can be obtained by improving the source–sink relationship during grain filling, whereas high nitrogen increased yield by improving plant growth rate during the critical period and kernel number. Implications Knowledge of source–sink relationship during effective filling period, plant growth during the critical period and kernel number may result in a more targeted selection program.