RESPONSE TO SELECTION OF A MAIZE POPULATION FOR ADAPTATION TO HIGH OR LOW NITROGEN FERTILIZATION

The adaptation of maize varieties to lower N-fertilization could become a selection goal for sustain- able agriculture. The question is then to know whether it is better to select at low N-input (direct selection) or at high N-input (indirect selection). To answer this question with specific material, a recurrent selection was devel- oped from the same population during two cycles, with two independent selections: one for adaptation to low N- input and the other for adaptation to high N-input. Popu- lations of each cycle were then evaluated with the initial population both at low and at high N-input. The results show a greater efficiency of indirect selection than of di- rect selection. This was interpreted as being due to a low- er heritability at low N-input, with higher environmental variance and genotype x environment interaction than at high N-input. After one cycle of selection, genetic vari- ance at low N-input was even lower than genetic variance at high N-input. During the two selection cycles there was no specific adaptation of the material to the breeding N- conditions. A low N-input environment appeared as an unfavourable environment for selection. The response to grain yield was associated with a decrease in kernel pro- tein content. However there was an increase in grain pro- tein yield.