Genetic variation for nitrogen use efficiency in Canada Western Red Spring wheat (Triticum aestivum L.) under conventional and organic management systems

  • Author / Creator
    Kubota, Hiroshi
  • Improved nitrogen use efficiency in cereal-based agricultural systems can contribute to increasing grain production while reducing agriculture-related pollution caused by nitrogen leaching, volatilization and denitrification. Organic agriculture differs to conventional systems in terms of in management practice, fertilization regimes, and the nature of nitrogen cycling. These differences affect nitrogen use efficiency and its associated traits. Therefore, breeding for improved nitrogen use efficiency in spring wheat (Triticum aestivum L.) requires adequate genetic variability for the traits according to the farming practice employed. Studies were carried out from 2010 to 2015 to evaluate differences in agronomic traits and genetic variation for nitrogen use efficiency traits in Canada Western Red Spring wheat cultivars under conventional and organic systems, and identified specific genotypes of high nitrogen use efficiency. Organically grown grain was earlier flowering, and had lower test weight grain yield compared to its conventional counterpart. Earlier maturity associated Vrn genes did not translate to any yield advantage under organic field conditions. There was a cross-over interaction of the genotypes between managements in grain protein content, indicating a necessity of specific cultivar choice/breeding for organic system. Under high and low nitrogen levels in conventional practices, genotype × fertilizer interaction was shown to be significant for important yield and nitrogen use efficiency traits. Correlations among traits were more pronounced under high nitrogen than low nitrogen treatment. The significant positive correlations between total dry matter at harvest and nitrogen uptake efficiency suggested that vigorous biomass production is an important driver for increased nitrogen uptake. Prominent effects of the Rht alleles on agronomic and nitrogen use efficiency traits were identified under high N conditions. However, the effect of the Rht-1b alleles on cultivar nitrogen uptake efficiency is inconsistent under high nitrogen condition, indicating that dwarfing Rht alleles have indirect mechanisms associated with nitrogen uptake. Genetic improvements were observed for grain yield, nitrogen use efficiency, and nitrogen utilization efficiency over the last century only in high nitrogen condition. These increases were mainly attributed to improved harvest index, suggesting an improvement in assimilate partitioning efficiency. Between conventional and organic farming systems, analysis of variance revealed significant effects of genotype, environment, and their interactions on grain and stem nitrogen yield, and nitrogen utilization efficiency under organic systems. Modern genotype, Superb, CDC Kernen, and CDC Stanley were superior and stable across the tested organic environments in several important traits including grain yield, and nitrogen use efficiency relative to other modern genotypes. These cultivars seemed to obtain high grain yield by different strategies. Breeding cultivars that possess characteristics of high grain and stem nitrogen yield with nitrogen use efficiency may be achievable by using potential genotypes such as Superb for organic cultivation systems to optimize the system sustainability while maintaining grain yield.

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  • Degree
    Doctor of Philosophy
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