Abstract: In order to explore the genetic basis for flowering date variation in alfalfa, a QTL mapping population was set up comprising 152 F₁ hybrids of 2 parent plants with contrasting maturity dates, and the QTL loci associated with flowering date were identified. A low-yielding early-maturing alfalfa variety was used as the pollen parent and a high-yield late-maturing variety was used as the seed parent. In 2015 and 2016, the date of initial flowering was recorded for the 152 F₁ hybrids and the 2 parent plants, and genotyping of the 154 single plants was carried out using GBS sequencing technology. The SNP markers generated were used to construct a linkage map, and QTL ici Mapping software and phenotypic data were used for QTL positioning of flowering time. A major gene and poly gene inheritance model was then used to build up the optimal genetic model for control of initial flowering time. The analysis indicated two major gene model-additive effect as the optimum genetic model for controlling date of initial flowering. The major gene heritability reached 99.0% in 2015, while it was 98.5% in 2016. The pollen-parent linkage map comprised 1386 cM and the average marker spacing was 3.2 cM. The female-parent linkage map covered 798.73 cM with an average marker spacing of 8.07 cM. Two main QTLs were found in both year’s data sets, with phenotypic variation accounted for being 12.13% and 11.02% respectively. In summary, date of initial flowering is largely determined by two major genes with additive effects. The initial time of flowering is mainly controlled by two QTL sites.

Key words: flowering trait, initial time of flowering, genetic analysis, genetic linkage map, QTL mapping