Divergent selection for grain protein affects nitrogen use in maize hybrids

The Illinois high (IHP), low (ILP), and corresponding reverse (IRHP, and IRLP) protein–strains of maize represent genetic extremes for differences in grain protein concentration. The objective of this study was to determine how divergent selection for grain protein affects N use in hybrid plants. Inbreds derived from the protein–strains were crossed as males to a common tester and the resultant hybrids evaluated at eight N rates in the field over 3 years. A more than two-fold difference in grain protein concentration was observed among the strain-hybrids with ILP averaging 65 g kg−1, IRHP 89 g kg−1, IRLP 111 g kg−1, and IHP 148 g kg−1 of grain protein. Except for IHP at the lowest N levels, the strain-hybrids were similar in their whole shoot biomass production both pre- and post-flowering. Conversely, the strain-hybrids differed markedly in their uptake and accumulation of plant N, and these differences were already evident at flowering before a grain sink was present. Although all hybrids had the same overall N use efficiency at maturity (approximately 24 kg kg−1 N), they differed in their N use components with IHP and IRLP exhibiting a higher uptake efficiency, and ILP and IRHP exhibiting high utilization efficiency. The remobilization of leaf N was also more extensive for IHP and IRLP. Changes in grain protein concentration from divergent selection were directly related to changes in uptake and use of N by the plant.