Grain composition and productivity of maize hybrids derived from the Illinois protein strains in response to variable nitrogen supply

The Illinois Long-Term Protein Selection strains of maize (Zea mays L.) have been employed in a variety of studies investigating the genetic and physiological control of maize grain composition. These prior studies, however, have not assessed the grain composition and yield potential of these strains in hybrid combinations with an elite tester, or in response to supplemental N. Our objective was to study the interactive effect of genotype and N supply on productivity and grain quality for hybrids with a wide divergence in grain protein. Hybrids derived from the Illinois Protein Strains were evaluated in a 2-yr field experiment where N rates were varied from 0 to 235 kg ha(-1) (in eight 34-kg increments), along with a current commercial hybrid sharing the same female parent (FR1064). The Illinois Protein Strain hybrids produced grain protein concentrations that reflected the strain parents, with all hybrids except Illinois Low Protein showing increased grain protein in response to increasing N supply. Many other strain attributes were also manifested at the hybrid level, including the relative differences in kernel weights and the inverse relationship between grain protein to both starch concentration and grain yield. Nitrogen supply positively enhanced grain yield in all hybrids, primarily by increasing kernel number. Nitrogen supply also impacted the yield-protein relationship by stimulating protein synthesis rather than by inhibiting starch production. These results demonstrate the strong genetic control of grain composition in maize hybrids, which can be modulated by the positive effects of N on reproductive sink capacity and seed protein synthesis.