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

Abstract

Translocation and assimilation of N during grain filling are involved in determining grain protein content in wheat ( Trificum aestivum L.). Considerable controversy on the physiological basis for high grain protein concentration exists. These aspects of N movement within the plant were studied in field experiments with the spring wheat cultivars Anza and Cajeme 71 and 96 F 5 lines from the cross of these cultivars. Cajeme 71 had higher grain protein concentration, higher translocation, translocation efficiency, and a higher proportion of N in the grain than Anza, but no relationship between any of these three parameters and grain protein concentnation was found in the F 5 lines. The ratio of N harvest index to grain harvest index, which gives a rough estimate of the relative proportioning of N and carbohydrate in the grain, was positively related to grain protein concentration ( r =0.39 to 0.45, P < 0.01), emphasizing the need to consider both N and carbohydrate partitioning while studying the genetic basis of high grain protein concentration. A relatively simple genetic basis was postulated for the observed variation. A two‐gene additive model fit the F 5 frequency distribution observed in both low and high N experiments. The F 5 lines that assimilated more N after anthesis than required for their yield level, identitied by regression of N assimilation after anthesis on grain yield (Le., high positive residuals), and that had high N translocation were found to be high in grain protein concentration. Excess assimilated N, the sum of translocation and these residuals (positive or negative), was closely related to grain protein concentration ( r =0.8 to 0.9, P < 0.01). Further, these data for excess N conform closely to theoretical calculations of the additional N requirement for a 1% increase in grain protein concentration.