Mapping quantitative trait loci for nitrogen uptake and utilization efficiency in rice (Oryza sativa L.) at different nitrogen fertilizer levels.

Genetic improvement is the fundamental basis for improving nitrogen-use efficiency. A better understanding of genetic factors controlling nitrogen uptake and utilization is required for crop genetic improvement. In this study, we identified the quantitative trait loci (QTLs) associated with traits of nitrogen uptake and utilization by using the single-sequence repeat marker method and a recombinant inbred line (RIL) population derived from a super hybrid Xieyou9308. All the traits investigated were inherited quantitatively by continuous variation and showed normal distribution in phenotype with transgressive segregation in the RIL population. Most of the traits were significantly correlated with each other except for nitrogen absorption ability (NAA) with nitrogen harvest index (NHI) and NHI with agricultural nitrogen-absorption efficiency (ANAE). At logarithmic odds value of 2.3, total 13 candidate QTLs, including 4 for NAA, 2 for NHI, 2 for physiological nitrogen-use efficiency, 1 for agricultural nitrogen-use efficiency (ANUE), and 4 for ANAE, were detected and mapped on chromosomes 2, 3, 4, 5, 8, 9, 10, and 12. Significant pleiotropic effect or neighboring expression of QTLs was observed among traits. At position 64.8 cM on chromosome 4 near the marker RM5757, there was a QTL cluster of NAA, ANUE, and ANAE, and at chromosome 5 near the marker RM5968, there was a QTL cluster of NAA and ANUE. The QTL clusters might provide partial explanation and genetic mechanism for the observed correlations between nitrogen uptake and utilization efficiency traits and might form a basis for future breeding programs.