Grain oil content is negatively correlated with starch content in maize in general. In this study, 282 and 263 recombinant inbred lines (RIL) developed from two crosses between one high-oil maize inbred and two normal dent maize inbreds were evaluated for grain starch content and its correlation with oil content under four environments. Single-trait QTL for starch content in single-population and joint-population analysis, and multiple-trait QTL for both starch and oil content were detected, and compared with the result obtained in the two related F2∶3 populations. Totally, 20 single-population QTL for grain starch content were detected. No QTL was simultaneously detected across all ten cases. QTL at bins 5.03 and 9.03 were all detected in both populations and in 4 and 5 cases, respectively. Only 2 of the 16 joint-population QTL had significant effects in both populations. Three single-population QTL and 8 joint-population QTL at bins 1.03, 1.04–1.05, 3.05, 8.04–8.05, 9.03, and 9.05 could be considered as fine-mapped. Common QTL across F2∶3 and RIL generations were observed at bins 5.04, 8.04 and 8.05 in population 1 (Pop.1), and at bin 5.03 in population 2 (Pop.2). QTL at bins 3.02–3.03, 3.05, 8.04–8.05 and 9.03 should be focused in high-starch maize breeding. In multiple-trait QTL analysis, 17 starch-oil QTL were detected, 10 in Pop.1 and 7 in Pop.2. And 22 single-trait QTL failed to show significance in multiple-trait analysis, 13 QTL for starch content and 9 QTL for oil content. However, QTL at bins 1.03, 6.03–6.04 and 8.03–8.04 might increase grain starch content and/or grain oil content without reduction in another trait. Further research should be conducted to validate the effect of these QTL in the simultaneous improvement of grain starch and oil content in maize.

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Plant traits play an important role in determining plant density and final grain yield. In this study, two related RIL populations developed from two crosses between one high-oil maize inbred and two normal dent maize inbreds were evaluated for 13 plant traits under four environments. QTL were detected within population and in joint-population analysis, and compared with the result obtained in the two F 2:3 generations. Our main objective was to find identical QTL and key genetic regions valuable in further research. Totally, 318 single-population QTL, 142 pairs of digenic epistasis and 412 joint-population QTL were detected. Joint-population analysis could detect much more QTL and increase the accuracy of QTL localization. Consistent QTL across generations, environments and analysis methods were observed for five traits at four bins. QTL for plant height and ear height at bin 3.05, and for leaf area at bin 6.03-6.04 had the highest consistency across most situations. These QTL with high consistency were worthy to be put into marker-assisted selection in trait improvement and to construct near isogenic lines in further research. Maize breeding could be improved by integrating marker assisted selection and phenotypic selection.