Genetic Variation for Nitrogen Remobilization and Postsilking Nitrogen Uptake in Maize Recombinant Inbred Lines: Heritabilities and Correlations among Traits

In maize (Zea mays L.), grain protein yield is the result of two nitrogen fluxes: N remobilization from stover to the kernels and N allocation to kernels from postsilking N uptake. Nitrogen-15 labeling was used to study these two fluxes. Genetic variation for N remobilization and postsilking N uptake was studied in testcrosses derived from a population of recombinant inbred lines. On average, from a 2-yr experiment, 28.3% of whole-plant N was taken up after silking, and 93% of this postsilking N uptake was allocated to kernels. Nitrogen remobilization represented around 61% of total grain N. However, there was greater variation for postsilking N uptake than for N remobilization. Consequently, N grain yield was more highly correlated with the amount of postsilking N uptake than with the amount of N remobilization. The amount of N remobilization was significantly correlated with both the whole-plant N amount present at silking and the proportion of N remobilized, whereas N from N uptake within kernels was only correlated to the postsilking N uptake. Variation for the proportion of postsilking N uptake allocated to kernels was low in comparison to that of postsilking N uptake. There was a negative correlation between the amount of N remobilization and the amount of postsilking N uptake, which appears to have a physiological basis. Finally, use of 15N labeling provided a better description of variation for N accumulation in kernels than the classical balance method.