IDENTIFICATION OF QUANTITATIVE TRAIT LOCI CONTROLLING HEADING DATE INRICE USING A HIGH-DENSITY LINKAGE MAP

Quantitative trait locus (QTL) analysis has been carried out to identi fy genes conferring heading date in rice. One hundred and eighty six F -2 plants derived from a cross between a japonica variety, Nipponbare, and an indica variety, Kasalath, were used as a segregating populatio n for QTL mapping and more than 850 markers were employed to identify QTLs. Scan-analysis revealed the existence of two QTLs with large effe cts, Hd-1 and Hd-2, one in the middle of chromosome 6 and one at the e nd of chromosome 7, respectively. For both loci, the Kasalath alleles reduced days-to-heading. In addition, three QTLs with minor effects, H d-3, Hd-4 and Hd-5, were found to be located on chromosomes 6, 7 and 8 based on a secondary scan analysis which was carried out by removing the phenotypic effects of Hd-1 and Hd-2. For the three secondary loci, the Nipponbare alleles reduced days-to-heading. The five QTLs explain ed 84% of the total phenotypic variation in the F-2 population based o n a multiple-QTL model. The presence of a digenic interaction between Hd-1 and Hd-2 was clearly suggested.