Soybean QTLs for Nitrogen and Ureides in Two Ril Populations Whose Parents Differ in Sensitivity of N2 Fixation to Drought.

Nitrogen fixation in soybean is sensitive to drought. N fixation was more tolerant to drought in soybean genotypes with low well-watered shoot-N concentration, without any apparent yield penalty associated with low shoot-N. Quantitative trait loci (QTLs) for shoot N and ureide concentrations were identified in two recombinant inbred line (RIL) populations [KS4895 x Jackson (KxJ) and KS4895 x PI424140 (KxP)] developed from parental lines differing for nitrogen fixation response to drought. For both RIL populations, broad-sense heritability for shoot-N and ureide concentrations ranged from 0.63 to 0.85 under irrigated conditions. Under drought conditions, heritability for shoot N was 0.22 to 0.24 and for ureide was 0.40 to 0.51. Composite interval mapping (CIM) indicated numerous QTLs for shoot N and/or ureide that overlapped between these two RIL populations and also with previously reported QTLs for N-associated traits in soybean. In previously published results for the KS4895 x Jackson 93705 RIL population, there were a total of nine QTLs identified for shoot N and ureide. Our data from the two RIL populations confirmed QTLs for shoot N/ureide for five of the nine QTLs reported previously on Gm9, Gm17, Gm19, and two on Gm13. We also identified novel QTLs for shoot N/ureide concentration in both the KxJ and KxP RIL populations on Gm10 and Gm11. In the KxP population, we identified a QTL for shoot ureide and N on Gm5 that overlapped with a previously reported QTL for specific leaf nitrogen.