Quantitative trait loci associated with flowering time in wild chrysanthemum (Chrysanthemum seticuspe)

The mechanisms of flowering-time (FT) regulation in cultivated chrysanthemum (Chrysanthemum morifolium) are essential for breeders owing to their significant effects on cultivation. The wild diploid Chrysanthemum seticuspe has the same short-day flowering habits as cultivated chrysanthemum. We investigated an F₂ segregating population derived from crosses of accessions with differences in FT for quantitative trait locus (QTL) mapping. Three major QTLs for FT were mapped, each overlapping with QTLs for other flowering traits: one QTL associated with a longer critical daylength and two QTLs linked to the ability to flower rapidly following floral transition under short-day conditions, one of which also contributes to flowering competence at high temperatures. These traits collectively influence the regulation of FT. Altered expression patterns of circadian-clock-related genes in SoS4-4, the early-flowering parental line, suggested altered rhythmicity of the circadian clock. Circadian-clock-related genes and a photoreceptor gene were also found in the FT QTL interval. These genes may be responsible for altering the circadian clock and causing variation in FT by changing the critical daylength.