Genetic loci in the photoperiod pathway interactively modulate reproductive development of winter wheat.

Responses to photoperiod and low temperature are the two primary adaptive mechanisms which enable wheat plants to synchronize developmental processes with changes in seasonal climate. In this study, the developmental process was characterized at two stages: stem length during the onset of stem elongation and heading date. These two developmental events were monitored and mapped in recombinant inbred lines (RILs) of a population generated from a cross between two complementary and locally adapted hard winter wheat cultivars. 'Intrada' undergoes stem elongation earlier but reaches heading later, whereas 'Cimarron' undergoes stem elongation later but reaches heading earlier. Variation in the developmental process in this population was associated with three major QTLs centered on Xbarc200 on chromosome 2B, PPD-D1 on chromosome 2D, and Xcfd14 on chromosome 7D. The Intrada Xbarc200 and Xcfd14 alleles and the Cimarron PPD-D1 allele accelerated both stem elongation and heading stages, or the Cimarron Xbarc200 and Xcfd14 alleles and the Intrada PPD-D1 allele delayed both stem elongation and heading stages. Integrative effects of the three QTLs accounted for 43% (initial stem length) and 68% (heading date) of the overall phenotypic variation in this population. PPD-D1 is a reasonable candidate gene for the QTL on chromosome 2D, PPD-B1 could be associated with the QTL on chromosome 2B, but VRN-D3 (=FT-D1) was not linked with the QTL on chromosome 7D, suggesting that this is a novel locus involved in winter wheat development. Because the PPD-D1 QTL was observed to interact with other two QTLs, all of these QTLs could play a role in the same pathway as involved in photoperiod response of winter wheat.