Functional stay-green is generally considered a desirable trait in major crop varieties including maize. Finding new loci and candidate genes related to stay-green, and providing new theoretical basis for the genetic research on stay-green.

Using 150 recombinant inbred lines (RIL) populations derived from the cross between Xu 178 and K12, QTL mapping of three stay-green related traits (visual stay green (VSG), green leaf number at silking stage (GLNS) and green leaf number at mature stage (GLNM) were performed by the composite interval mapping (CIM) method of Windows QTL Cartographer V2.5. Besides, an association population, which composed of 139 natural materials genotyped with 50790 high-quality SNP markers, was used to dissect genetic locus of three traits by genome-wide association study (GWAS) based on the mixed linear model MLM).

Based on CIM, three traits (GLNM, GLNS and VSG) were mapped using phenotypic values in a single environment and best linear unbiased prediction (BLUP) value. A total of 37 QTLs were detected on all chromosomes except Chromosome 10, and the LOD score ranged from 2.58-11.36, with a phenotypic variation contribution rate of 4.34%-22.40%. Among them, 14, 12 and 11 loci were detected for GLNM, GLNS and VSG traits, respectively. Four of the QTLs, qGLNS2-1, qVSG1-1, qVSG1-2 and qVSG7-1, were genetically stable and were detected simultaneously in three or more different single environments. GWAS was performed on three stay-green related traits using MLM, and a total of 44 significant SNPs above the threshold line were detected. According to the physical position of SNP markers in the B73 reference genome, a total of 15 SNP were found to fall into the QTL interval mapped by linkage analysis.

Combined with the results of QTL mapping and genome-wide association study, a total of 4 genetically stable colocalization genetic regions were detected (the corresponding physical position intervals on the B73 reference genome version 4 are 6.2-8.2 Mb on chromosome 1, 209.1-221.4 Mb on chromosome 2, 96.8-102.1 Mb on chromosome 6, and 4.9-11.4 Mb on chromosome 7), and four important candidate genes (Zm00001d006119, Zm00001d018975, Zm00001d006535 and Zm00001d036763) related to photosynthesis and stress response were mined.