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Genetic Variation for Nitrogen Assimilation and Translocation in Wheat. II. Nitrogen Assimilation in Relation to Grain Yield and Protein¹

An understanding of the relationship between N assimilation and grain yield and protein, and the measurement of genetic variation in preanthesis and postanthesis N assimilation in wheat (Triticum aestivum L.) are necessary to achieve additional gains in selecting for both high grain yield and high grain protein. Thus, total N assimilation in the spring wheat cultivars ‘Anza’ and ‘Cajeme 71’ and 96 F5-lines from the cross of these cultivars was studied in field experiments. Freanthesis N assimilation was similar for the two cultivars, but by maturity Anza had assimilated 9% (P < 0.01) more N than Cajeme 71 in both high and low N fertility levels. This difference was mainly due to greater postanthesis assimilation by Anza (22% of total) than Cajeme 71 (10%). Significant genetic variation among F5 lines in N assimilation prior to anthesis occurred in two of three experiments, but no relationships were found between this trait and grain yield, grain protein concentration, or grain protein yield. Significant genetic variability in N assimilation after anthesis was detected, although estimates of heritabilities were low. Nitrogen assimilation after anthesis strongly influenced grain and grain protein yields, explaining 27 to 39% of the variation, but no relationship was found with grain protein concentration. The residuals from the regression of N assimilation after anthesis on biomass at anthesis were also strongly related to grain and grain N yield in a stagewise regression analysis, indicating variation other than random error was involved. Grain protein concentration was also positively associated with these residuals in one experiment. Possible sources of this variation, particularly with relation to roots are discussed. Total N assimilation showed broad-sense heritabilities of 21 to 27% and was correlated (r = 0.68 to 0.86; P < 0.01) with grain and grain protein yields. Thus genetic variation in N assimilation has a role in determining grain yield and protein concentration in wheat. Further work to determine the genetic and physiological basis of factors influencing N assimilation is needed, especially with regard to roots.

Key Words: Triticum aestivum L. • Stagewise regression

² Former graduate student (presently rice breeder, Queensland Dep. of Primary Ind., P. O. Box 591, Ayr, Qld. 4807, Australia) and professors of agronomy, Univ. of California, Davis, respectively.

Received for publication January 30, 1984.