Mapping of QTLs conferring extremely early heading in rice (Oryza sativa L.).

Two genes related to extremely early heading were identified in populations derived from crosses between Hoshinoyume, a variety adapted to the northernmost limit of rice cultivation (Hokkaido), and Nipponbare, a variety adapted to the temperate region of Japan. The segregations for heading date clearly revealed that a two-gene model determined the extremely early heading in the F(2) and BC(1)F(1) populations under natural field conditions in Hokkaido. Using molecular markers corresponding to ten known quantitative trait loci (QTLs) for heading date, we carried out QTL analysis in the BC(1)F(1) population and detected two QTLs, qDTH-7-1 and qDTH-7-2, both on chromosome 7, and observed epistatic interaction between them. We conclude that the recessive alleles of these two genes contribute to extremely early heading for the adaptation to Hokkaido environment and to stable rice production in Hokkaido. The relationships between the two QTLs identified in this study and known QTLs are discussed.