QTL mapping for seedling traits under different nitrogen forms in wheat

The uptake and utilization of nitrogen (N) by plants are affected by the different forms of N in the soil. In this study, eight morphological traits at the seedling stage were investigated using a set of recombinant inbred lines (RILs). Three hydroponic culture experiments were conducted using three different NO₃ ^?/NH₄ ⁺ ratios (T1 at 50/50 %, T2 at 100/0 % and T3 at 0/100 %). The investigated traits in T2 and T1 were significantly higher than T3 in all three experiments, indicating that NO₃ ^? promoted or NH₄ ⁺ suppressed the production of biomass. Comparing T1 with T2, NO₃ ^? significantly increased the values of root fresh weight (RFW), total fresh weight (TFW) and root dry weight (RDW) and significantly decreased shoot dry weight (SDW). A total of 147 quantitative trait loci (QTLs) for the eight traits were detected on 18 chromosomes (except 2A, 3D and 4D). Among them, 16 QTLs (QRfw-1A, QRfw-1D, QSfw-1D, QSfw-2B.1, QTfw-1A, QTfw-1D, QRsfw-2B, QRsfw-3B.1, QRdw-1A.1, QRdw-1A.2, QSdw-6B.1, QSdw-7A.1, QTdw-1A.1, QRsdw-1A.1, QRsdw-5A.1 and QRsdw-7A.1) were detected in more than three of the nine treatment–experiments, and most of the 16 QTLs made large contributions of approximately 15 %. Surprisingly, QRsfw-4A.1 and QRsfw-4A.2 explained as much as 47.9 and 55.5 % of the phenotypic variation, respectively. Thirteen important QTL clusters (C1-C13) with more than four QTLs and involving 66 QTLs (44.9 %) were mapped on chromosomes 1A, 1D, 2B, 2D, 4A, 4B, 5B, 5D, 6B, 7A and 7B.