Mapping of QTL for agronomic traits using high-density SNPs with an RIL population in maize.

BACKGROUND: Genome wide association studies (GWAS) have been widely used to identify QTLs underlying quantitative traits in humans and animals, and they have also become a popular method of mapping QTLs in many crops, including maize. Advances in high-throughput genotyping technologies enable construction of high-density linkage maps using SNP markers. OBJECTIVES: High-density genetic mapping must precede to find molecular markers associated with a particular trait. The objectives of this study were to (1) construct a high-density linkage map using SNP markers and (2) detect the QTLs for grain yield and quality related traits of the Mo17/KW7 RIL population. METHODS: In this study, two parental lines, Mo17 (normal maize inbred line) and KW7 (waxy inbred line) and 80 F7:8 lines in the Mo17/KW7 RIL population were genotyped using the MaizeSNP50 BeadChip, an Illumina BeadChip array of 56,110 maize SNPs. Marker integration and detection of QTLs was performed using the inclusive composite interval mapping (ICIM) method within the QTL IciMapping software. RESULTS: This study was genotyped using the Illumina MaizeSNP50 BeadChip for maize Mo17/KW7 recombinant inbred line (RIL) population. The 2904 SNP markers were distributed along all 10 maize chromosomes. The total length of the linkage map was 3553.7 cm, with an average interval of 1.22 cm between SNPs. A total of 18 QTLs controlling eight traits were detected in the Mo17/KW7 RIL population. Three QTLs for plant height (PH) were detected on chromosomes 4 and 8 and showed from 16.01% (qPH8) to 19.85% (qPH4a) of phenotypic variance. Five QTLs related to ear height (EH) were identified on chromosomes 3, 4, and 6 and accounted for 3.79% (qEH6) to 27.57% (qEH4b) of phenotypic variance. Five QTLs related to water content (WC) on chromosomes 1, 4, 8, and 9 accounted for 9.55% (qWC8b) to 23.30% (qWC4) of phenotypic variance. One QTL (qAC9) relating to amylose content (AC) on chromosome 9 showed 82.10% of phenotypic variance. CONCLUSIONS: The high-density linkage map and putative QTLs of the maize RIL population detected in this study can be effectively utilized in waxy and normal maize breeding programs to facilitate the selection process through marker-assisted selection (MAS) breeding programs.

Genetic characterization and association mapping in near-isogenic lines of waxy maize using seed characteristics and SSR markers.

BACKGROUND: Association mapping has been advocated as the method of choice for identifying loci involved in the inheritance of complex traits in crop species. This method involves identifying markers with significant differences in allele frequency between individuals with a phenotype of interest and a set of unrelated control individuals. OBJECTIVE: The purpose of our study is not only to investigate the genetic diversity and relationships of the basic molecular markers of near-isogenic lines (NILs) of waxy maize, but it is also to identify molecular markers related to interesting seed characteristics including 4 seed quantity traits and 4 seed phenotypic traits using association analysis with population structure. METHODS: We performed association mapping of 200 SSR markers and 8 seed characteristics among 10 NILs of waxy maize and two parental lines (HW3, HW9) (recurrent parent) of "Mibaek 2" variety. RESULTS: In population structure and cluster analysis, the 10 NILs and two parental lines were divided into two groups. Seven inbred lines, including HW3, were assigned to Group I. Group II contained 5 inbred lines, including HW9. In addition, we found that 32 SSR markers associate with 8 seed characteristics in 10 NILs. In particular, five SSR markers (umc1986, umc1747, umc2275, phi078, umc1366) were together associated with more than one seed characteristics such as EL, 100 KW, SCC, R, L*, and V. CONCLUSION: This study demonstrated the utility of SSR analysis for studying GD, population structure, and association mapping in 10 NILs and two parental lines (HW3, HW9) of "Mibaek 2" variety.

Construction of genetic linkage map and identification of QTLs related to agronomic traits in DH population of maize (Zea mays L.) using SSR markers.

BACKGROUND: In this study, we used phenotypic and genetic analysis to investigate Double haploid (DH) lines derived from normal corn parents (HF1 and 11S6169). DH technology offers an array of advantages in maize genetics and breeding as follows: first, it significantly shortens the breeding cycle by development of completely homozygous lines in two or three generations; and second, it simplifies logistics, including requiring less time, labor, and financial resources for developing new DH lines compared with the conventional RIL population development process. OBJECTIVES: In our study, we constructed a maize genetic linkage map using SSR markers and a DH population derived from a cross of normal corn (HF1) and normal corn (11S6169). METHODS: The DH population used in this study was developed by the following methods: we crossed normal corn (HF1) and normal corn (11S6169), which are parent lines of a normal corn cultivar, in 2014; and the next year, the F1 hybrids were crossed with a tropicalized haploid inducer line (TAIL), which is homozygous for the dominant marker gene R1-nj (Nanda and Chase in Crop Sci 6:213-215, 1966), and we harvested seeds of the haploid lines. RESULTS: A total of 200 SSR markers were assigned to 10 linkage groups that spanned 1145.4 cM with an average genetic distance between markers of 5.7 cM. 68 SSR markers showed Mendelian segregation ratios in the DH population at a 5% significance threshold. A total of 15 quantitative trait loci (QTLs) for plant height (PH), ear height (EH), ear height ratio (ER), leaf length (LL), ear length (EL), set ear length (SEL), set ear ratio (SER), ear width (EW), 100 kernel weight (100 KW), and cob color (CC) were found in the 121 lines in the DH population. CONCLUSION: The results of this study may help to improve the detection and characterization of agronomic traits and provide great opportunities for maize breeders and researchers using a DH population in maize breeding programs.