Genetic variation for nitrogen use efficiency in a set of recombinant maize inbred lines I. Agrophysiological results

To avoid pollution by nitrates and to maintain a sufficient net income, the farmer must optimize the use of nitrogen fertilizer. Using Varieties with a better nitrogen use efficiency (NUE) is a way Co reach such an objective. To study the genetic variability and genetic basis of NUE in maize(Zea mays L.) a set of 99 recombinant inbred lines crossed to a rester was studied for grain yield and other traits, including N content, in comparison to commercial varieties, at low input (N-) and high input (N+), during two years in one location. From N+ to N- grain yield was reduced by 38%, kernel number by 32% and kernel weight by 9%. Vegetative development was reduced by 14% whereas the growth after anthesis was reduced by 21%. N uptake efficiency (NUpE) was reduced by 35% at harvest whereas N utilization efficiency (NUtE) was increased by 27%. Genotype x nitrogen (G x N) interaction variance was significant for yield and kernel number, brit not for kernel weight. G x N interaction for kernel number was highly correlated to the interaction observed for yield. Responsiveness for yield or kernel number was negatively correlated to yield in N-. Heritability was decreased in N-. Differences in grain yield were easier to explain in N- than in N+. Vegetative development was favourable in both N conditions. In N-, N uptake and nitrogen nutrition index at silking were positively correlated to grain yield whereas leaf senescence and anther-silking interval were negatively correlated. NUE was explained both by NUpE and NUtE. However NUpE was more variable in N+ than in N- and the reverse for NUtE. Limiting steps in N metabolism appears to be different at low and high levels of N fertilizer.