Genomic regions involved in response to grain yield selection at high and low nitrogen fertilization in maize.

In order to validate the role of genomic regions involved in nitrogen use efficiency and detected in a population of recombinant inbred lines (RIL), we have applied from the same population a recurrent selection for adaptation to low N-input (N0) and to high N-input (N1). Variation of allele frequency at neutral marker during the two cycles of recurrent selection may provide information about markers linked to QTLs. Significant temporal variation of allele frequency was investigated using the test of Waples, which tests the hypothesis of genetic drift versus selection. Most genomic regions (12/19) responding to selection were detected for selection at high N-input and only two were common to selection at high and low N-inputs. This was consistent with the greater grain yield response to selection observed for the population selected under high N-input compared with the population selected under low N-input, when they were evaluated at high N-fertilization. In contrast, when they were evaluated at low N-input both types of selection gave similar yield. As was expected, in the first cycle we observed selection of markers linked to grain yield QTLs. In the course of the second cycle three situations were observed: the confirmation of most regions already selected in C1 including all C1 regions overlapping with grain yield QTLs; the non-confirmation of some C1 regions (2/9); and the identification of new genomic zones (10/17). The detected marker-QTL associations revealed the consistency of the involvement of some traits, such as root architecture and glutamine synthetase activity, which would be of major importance for grain yield setting whatever the nitrogen fertilization.