Objectives Leaf is the important organ for photosynthesis, transpiration and resistance in crops. The purpose of this study was to provide an important theoretical basis for breeding maize cultivars with high sunlight utilization efficiency, to dissect genetic variation of maize leaf-related traits under normal and no nitrogen application, and to map related QTLs.
Methods Using maize backbone Zong3 as the donor and Xu 178 as the acceptor, a total of 166 single segment substitution lines (SSSLs) of maize backbone Zong3 were constructed with Xu 178 as the background by means of hybrid, backcrossing and molecular marker assisted selection. All the SSSLs and Xu 178 were treated under normal (N+) and no N supply (N–) conditions in field plot experiment. The experiments were conducted in Guiyang and Dejiang City of Guizhou Province and Luoping City of Yunnan Province. The leaf area (LA), chlorophyll content (CC) and number of green leaves under ear (NGLE) were investigated.
Results Across the whole genomes, 42 leaf-related traits QTLs were identified under both N+ and N– conditions and located on ten chromosomes. Under N+ treatment, we identified 8 QTLs related to leaf area, 5 QTLs related to green leaf number under ear, and 8 chlorophyll content QTLs at the three experimental sites. qLAI1b was detected in all the three sites, and it contributed 14.41%, 14.47% and 16.38% of phenotypic variation in Dejiang, Guiyang and Luoping, respectively. The allele from Zong3 exaggerated the phenotypic effects. Besides, the QTLs (qLN7a and qLN7b) related to the number of green leaves under ear were detected in the three experimental sites. Under N– treatment, we identified 9 QTLs related to LA, 7 QTLs related to NGLE, and 8 chlorophyll content QTLs at the three experimental sites. Among them, QTL qLAI3b, which was located on bin3.08, whose fragment size was 120.48 cM, and it contributed 20.4% (Dejiang), 12.8% (Guiyang) and 13.2% (Luoping), respectively. The allele from Xu178 synergistic the phenotypic effects. QTL qLN9 (umc1957～umc1867～umc2078), which was located in bin9.01, whose fragments size was 62.7 cM. QTL qCHL4a, which was located on bin4.08, whose fragment size was 18.69 cM, and it contributed 17.6% (Dejiang), 10.6%（Guiyang）and 11.4% (Luoping), respectively. The allele from Zong3 exaggerated the phenotypic effects.
Conclusions Two QTLs are detected under two nitrogen treatments, one is qLAI3b, which is located on Bin3.01 with flank markers of umc1844～umc1320～bnlg1182, and the other are qLN7a and qLN7b, which are located on bin7.01 and bin7.05 with flank markers of umc1642～umc2160～umc1929 and phi328175. These loci may play important roles in nitrogen absorbing, transporting and utilization during maize development, and served important candidate loci in further map-based cloning of maize leaf-related traits.
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