Nitrogen Utilization Efficiency: Relationships with Grain Yield, Grain Protein, and YieldRelated Traits in Rice
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Rice (Oryza sativa L.) breeders have historically not included nitrogen utilization efficiency (NUE) as a selection criterion in breeding for cultivars, even though it has economic and ecological implications. This study examined the significance and magnitude of variation in N content, NUE, N translocation ratio (NTR), and grain protein concentration among diverse rice genotypes. Fifteen rice genotypes were studied representing the combinations of low and high levels of four yield-related traits: maximum number of tillers, grain mass, main culm panicle node number, and panicle mass. These genotypes included 'Lemont', Teqing', and 13 advance recombinant inbred genotypes obtained from a Lemont x Teqing cross. Field data were obtained from experiments conducted during two cropping seasons. Plant samples were analyzed for N concentration. There was significant variation in N content and NUE among genotypes. The genotype NUE means ranged from 25.3 to 63.9 kg grain kg-1 N in a square meter of plants (kg grain kg-1 N), with the top four NUE values ranging from 56.6 to 63.9 kg grain kg-1 N. Nitrogen content and NUE were not significantly correlated with each other, and they had significant positive direct effects on grain yield. Grain yield was positively correlated with NUE, N content, and NTR, whereas NTR was correlated with grain protein concentration. Plant breeders could use these significant correlations to their advantage in breeding for rice cultivars that not only produce high yield but also utilize N efficiently and produce grain with a higher protein concentration. American Society of Agronomy.