Mapping QTLs for seed dormancy and the Vp1 homologue on chromosome 3A in wheat

A major component of the observed genetic variation for pre-harvest sprouting in wheat (Triticum aestivum L.) appears to be the level of seed dormancy. Group 3 chromosomes have received attention as carrying the R genes for seed-coat color and the taVp1 genes that are orthologous to the maize Vp1 gene which encode a dormancy-related transcription factor. The objectives of the present study were to map quantitative trait loci (QTLs) for seed dormancy on chromosome 3A and to investigate an association between taVp1 or R-A1 and the QTLs detected. A mapping population in the form of recombinant inbred lines developed from the cross between the highly dormant Zenkoujikomugi (Zen) and Chinese Spring (CS) was utilized. Nineteen marker loci, including taVp1, were mapped on chromosome 3A. The taVp1 locus was located in the middle of the long arm, about 85 cM from the centromere. The population was evaluated in duplicate by growing them under controlled environment conditions. Two QTLs for seed dormancy, designated as QPhs.ocs-3A.1 and QPhs.ocs-3A.2, were identified on the short and long arms, respectively. QPhs.ocs-1 explained 23-38% of the phenotypic variation and the Zen allele had a striking effect on maintaining dormancy. QPhs.ocs-2, with a minor effect, was detectable only at the dormancy-breaking stage. Although QPhs.ocs-2 was loosely linked to taVp1 by around 50 cM, they are clearly distinct genes. Zen and CS carry the white R-A1a allele, and no QTL effect was detected in the vicinity region of R-A1. Hence it was concluded that the high dormancy associated with chromosome 3A of Zen is ascribable to QPhs.ocs-1 on the short arm but is not due to the direct contribution of either the taVp1 or R-A1 locus.