Genetic Control of Nitrogen Uptake and Translocation in Maize1

Hybrid combinations of 10 flint with nine dent inbred lines of maize (Zea mays L.) along with 10 standard cultivars were evaluated in two environments. Four flint and four dent inbred lines were the result of a breeding program for high protein percentage in the grain and good combining ability for agronomic traits. The materials were harvested at two stages, i.e. at the beginning of the grain‐filling period and at grain maturity. Data based on stover, ear, and grain were collected to study N translocation from stover to ear during the grain‐filling period and N uptake in two phases of plant growth: the pre‐grain‐filling period (phase 1) and the grain‐filling period (phase 2). Highly significant differences were observed due to general combining ability (GCA) and specific combining ability (SCA) for total N uptake, N uptake in phase I, N uptake in phase 2, and N translocation. Genotype ✕ environment interactions involving both GCA and SCA contributed significantly to the variation for these traits. A high N uptake in phase 1 accompanied by a low N uptake in phase 2 seemed to increase the N translocation, depending on the capacity of the sink. The experimental hybrids, with high protein percentage and protein yield of grain, generally silked later than the conventional hybrids, but were at least comparable for percent ear dry matter at maturity and grain yield. This indicated a high rate of ear dry matter production and drying of the high‐protein hybrids. It is hypothesized that a high protein percentage and protein yield of mature grain, may be due to an intensive N uptake, a prolongation of the N uptake phase, and a high N translocation. The relative importance of these factors may vary in different genotypes and environments.