Mapping of quantitative trait loci controlling heading date among rice cultivars in the northernmost region of Japan

Heading date is the major factor in the regional and seasonal adaptation of rice cultivars. Although many genes controlling heading date have been identified using several mapping populations, it is not clear which previously identified genes contribute to the variation of heading date in particular regions. However, great effort is needed to identify quantitative trait loci (QTLs) among rice cultivars in rice breeding programs in a particular region because they are genetically closely related. In this study, we identified QTLs controlling]leading date in 3 F, Populations among rice cultivars in Hokkaido, the northernmost region of Japan. The segregations of heading date were continuous in all Populations. For QTL analysis in populations with genetically close relationships, we used SSR markers located near the known QTLs for the heading date. Three QTLs for the heading date, qDTH3, qDTH-6-1, and qDTH6-2, were detected on chromosomes 3 and 6. The relationships between the three QTLs identified in this study and the known QTLs are discussed.