Domestication affects nitrogen use efficiency in foxtail millet

Enhancing nitrogen use efficiency (NUE) in crops, particularly under limited nitrogen availability, is pivotal for advancing sustainable agricultural practices. This study investigates the NUE and associated physiological responses in foxtail millets (Setaria spp.) subjected to varying nitrogen regimes. We selected two genotypes of S. viridis and four of S. italica, representing three distinct domestication stages. The study employed four nitrogen treatments: 0 mg/kg (N0), 25 mg/kg (N25), 50 mg/kg (N50), and 100 mg/kg (N100), ranging from nitrogen deficiency to sufficiency. Our findings highlight marked variances in phenotypic adaptations to nitrogen availability among these domestication stages. Notably, wild genotypes (Q4, Q23) performed well in lower nitrogen conditions, evidenced by substantial increases in shoot and root biomass. Conversely, cultivated genotypes (Yugu18, C28) flourished predominantly under higher nitrogen conditions, displaying significant growth in shoot and root biomass, alongside improvements in root length, surface area, and volume. A critical observation was that under nitrogen-limited conditions, wild genotypes exhibited superior NUE compared to their cultivated counterparts. Structural equation modeling (SEM) elucidated a positive correlation between NUE and root architecture in wild genotypes, contrasted by a negative association with plant nitrogen content. Our findings indicate that modern elite varieties do not perform as well as the wild species in adapting to poor soil conditions. Physiological responses to N fluctuation in foxtail millet is likely under selection during domestication and breeding processes.