Detection and validation of QTLs for flowering time in morning glory

Japanese morning glory (Ipomoea nil), a short day plant, has been used for studying flowering times. Here, quantitative trait loci (QTL) analysis for days from sowing to flowering (DTF) of F₂ between I. nil var. Tokyo Kokei Standard (TKS) and I. hederacea line var. Q65, an early flowering variety, revealed seven QTLs: QTL Ipomoea Flowering 1-7 (qIF1-7). The position of qIF3, which had the most significant effect among the seven QTLs, corresponds with that of I. nil (or I. hederacea) CONSTANS (InCO/IhCO) in the linkage map. There is a single-base InDel in the coding sequence of InCO/IhCO. The single-base deletion (SBD) causes a frame-shift mutation and loss of function in TKS allele (inco-1). I. nil accessions bearing inco-1 tend to flower early, similarly to rice varieties bearing the loss of function allele of CO ortholog, hd1. The TKS allele of qIF3 reduces DTF and corresponds with the inferred effect of inco-1. Based on the distribution of inco-1, a hypothesis was proposed that the SBD in inco-1 might have played an important role in the expansion of Japanese morning glories, originally native to the tropical regions of the Americas, into temperate Asia.