Theor Appl Genet (1998) 97 : 103 —109  Springer-Verlag 1998 R. N. Sarma · B. S. Gill · T. Sasaki · G. Galiba J. Sutka · D. A. Laurie · J. W. Snape Comparative mapping of the wheat chromosome 5A Vrn-A1 region with rice and its relationship to QTL for flowering time Received: 23 December 1997 / Accepted: 12 January 1998 Abstract The vernalization gene Vrn-A1 on chromo- some 5A is the predominant gene determining the spring/winter habit difference in bread wheat. Vrn-A1 was physically mapped using a set of deletion lines which located it to the region of chromosome 5A flan- ked by deletion breakpoints 0.68 and 0.78. This interval was shown to be homoeologous to a region of rice chromosome 3 that contains the flowering-time QTL Hd-6, previously mapped in a NipponbareKasalath cross, and FLTQ1, a novel QTL identified by analysis of 78 F  families derived from a cross of ‘IR20’‘63—83’. Possible relationships between Vrn-A1 and rice QTL are discussed. Analysis of the chromosome 5A deletion lines showed evidence for a second, more proximal flowering-time effect located between deletion break- points 0.56 and 0.64. The proximal part of chromosome 5A is homoeologous to rice chromosome 9, on which two QTL were detected in the ‘IR20‘63—83’ cross. The possible relationship between these effects is also discussed. Key words Comparative trait mapping · Deletion mapping · Flowering time · QTLs · Vernalization response Communicated by G. Wenzel R. N. Sarma · D. A. Laurie · J. W. Snape ( ) John Innes Centre, Norwich Research Park, Colney, Norwich, NR4 7UH, UK Fax: #44 1603 452571 E-mail: john.snape@bbsrc.ac.uk B. S. Gill Department of Plant Pathology, Kansas State University, Manhattan, KS 66508-5502, USA T. Sasaki Rice Genome Research Program, National Institute of Agrobiological Resources, Tsukuba, Ibraki, Japan G. Galiba · J. Sutka Agricultural Research Institute of Hungarian Academy of Sciences, H2467, Martonvasar, Hungary Introduction Flowering time is an important criterion for regional adaptation and yield in all cereals. In rice (Oryza sativa L., 2n"2x"24) flowering time has been shown to be determined by the basic vegetative growth phase (BVG) and photoperiod sensitivity (PS). Two genes conferring PS, Se-1 and Se-2, have been mapped onto rice chromosomes 6 and 7, respectively (Kinoshita and Takahashi 1991; Mackill et al. 1993). Several other genes conferring PS (Se-3, Se-4, E-1, E-2, E-3) have been reported, but their chromosomal locations are still un- certain (Sato et al. 1988; Tsai 1995; Kinoshita and Takahashi 1991; Yokoo and Okuno 1993). Flowering- time quantitative trait loci (QTL) mapped in relation to restriction fragment length polymorphism (RFLP) markers include loci Hd-1, Hd-2, Hd-3, Hd-4, Hd-5 and Hd-6 mapped in a Nipponbare x Kasalath population (Yamamoto et al. 1996; Yano et al. 1997). In bread wheat (¹riticum aestivum L., 2n"6x"42), an initial need for a period of growth at low temper- ature to initiate flowering (vernalization response) distinguishes winter wheats from spring wheats, which have little or no vernalization response. Several loci for vernalization response have been identified, and their chromosomal locations have been estab- lished (Law 1976; Snape et al. 1985). Among these, the Vrn-A1 (formerly Vrn1) locus has been found to predominate and has been mapped onto the long arm of chromosome 5A (Galiba et al. 1995). This locus has been shown to form a homoeologous series with Vrn-B1 (formerly Vrn2) on chromosome 5B and Vrn-D1 (formerly Vrn3) on chromosome 5D ( Snape et al. 1997). A comparison of a common set of RFLP markers suggests that the Vrn-A1 locus is homologous to Sh  (Sgh2), the vernalization gene of barley mapped on chromosome 5H by Laurie et al. (1995), and to Sp1, another vernalization-response lo- cus mapped on to the 5R chromosome of rye (Plaschke et al. 1993).