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 to reach sucl an objective. To study the genetic variability and genetic basis ot NUE in maize(Zea mays L.) a set of 99 recombinant inbred lines crossed to a tester 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 29%. 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, but 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.