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Grain and Plant Protein Relationships in Hard Red Spring Wheat¹

Genetic variation for characters, related to N utilization and their relative contribution to grain protein percentage, grain protein yield, and grain yield was studied in 30 selected spring wheat (Tritieura aestivura L.) genotypes over four environments. These genotypes differed for all measured traits. Grain protein concentration was negatively correlated (P 0.05) with grain yield and grain protein yield. Total plant N at maturity was not correlated with grain protein concentration. Total plant N at anthesis amounted to 93% of the total plant N at maturity. High, positive correlations were found between biomass at anthesis and total plant N at anthesis and between biological yield and total N at maturity. Plant height was not correlated with biological yield or total N at maturity. Nitrogen harvest index was negatively correlated with grain protein concentration and was positively correlated with harvest index. Stepwise regressive analyses, which included grain protein concentration, grain protein yield, and grainyield as dependent variables, indicated that harvest index was the first independent variable to be included in each of the three equations. The harvest index coefficient was negative in the case of grain protein concentration and positive in the case of grain protein yield and grain yield. Total N at maturity, with a positive coefficient, was the only variable in addition to harvest index which was determined to be important in the grain protein yield equation. Important variables, in addition to harvest index, for the grain protein concentration equation were biological yield, with a negative coefficient, and N harvest index and total N at maturity with positive coefficients. Thus, although N harvest index and grain protein concentration were negatively correlated, their relationship became positive when harvest index was taken into account first in the regression equation. Increases in N harvest index or total N at maturity may increase grain protein percentage and grain protein yield without reducing yield. However, there is a need to identify additional variability for N harvest index and total N at maturity if significant gains are to be made.

Key Words: Triticum aestivum L. • Nitrogen harvest index • Harvest index • Stepwise regression analysis • Grain protein • Plant protein

² Former graduate research assistant (now professor, Univ. Nacional de Mar del Plata, Facultad de Ciencias Agrarias, c.c. 276-7620 Balcare, Argentina), assistant scientist, and research geneticist and professor, USDA-ARS, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication March 25, 1984.