Detection of QTLs for heading time and photoperiod response in wheat usinga doubled-haploid population

The genetic basis of heading time in wheat (Triticum aestivum L.) was inves tigated through the study of flowering under normal autumn sown field condi tions as well as photoperiod responses under a controlled environment. Quan titative trait loci (QTLs) for these traits were mapped in a doubled-haploi d (DH) population derived from a cross between the wheat cultivars 'Courtot ' and 'Chinese Spring'. A molecular marker linkage map of this cross that w as previously constructed based on 187 DH lines and 380 markers was used fo r QTL mapping. The genome was well covered (85%) except for chromosomes 1D and 4D, and a set of anchor loci regularly spaced over the genome (one mark er each 15.5 cM) was chosen for marker regression analysis. The presence of a QTL was declared at a significance threshold of alpha = 0.005. The popul ation was grown under field conditions in Clermont-Ferrand, France during t wo years (1994-1995), in Norwich, U.K. over one year (1998), and also under controlled environments in Norwich. For each trait, between 2 and 4 QTLs w ere identified with individual effects ranging between 6.3% and 44.4% of th e total phenotypic variation. Two QTLs were detected that simultaneously af fected heading time and photoperiod response. For heading time, these two Q TLs were detected in more than one year. One QTL located on chromosome arm 2BS near the locus Xfbb121-2B, co-segregated with the gene Ppd-B1 known to be involved in photoperiod response. This chromosome region explained a lar ge part of the variation (23.4-44.4% depending on the years or the traits). Another region located on chromosome arm 7BS between the loci Xfbb324-7B a nd Xfbb53-7B also had a strong effect (7.3-15.3%). This region may correspo nd to a QTL for earliness per se.