Genetic linkage of an unknown gens controlling awn length and Vrn-D1 gene in bread wheat

Vernalization genes (Vrn) control wheat growth habit (spring and winter habit). These genes play a key role in flowering time and earliness of bread wheat and are of great interest in wheat drought tolerance studies. In a research that was designed to develop isogenic lines for Vrn-B1 and Vrn-D1 genes, in the BC5F5 generation of Roshan (recipient parent) and Excalibur (donor parent), some isogenic lines were awned. Since the recurrent parent was awnless and the genetic background of the isogenic lines were similar with a probability of 99.99%, the possibility that the awn controlling gene is independent of the Vrn-B1 and Vrn-D1genes was rejected. Results showed that the awned and awnless isogenic lines carry Vrn-D1 and Vrn-D1a alleles, respectively. Therefore, the evidence can confirm the association of a gene controlling awn and Vrn-D1. The hypotheses of genetic linkage and pleiotropic effect were proposed to explain this association. To find the genetic reason for this relationship, in addition to Roshan and Excalibur, Rakhshan, Shahpasand, Mahdavi and Kalhaydari cultivars were also genetically evaluated. The results showed that Shahpasand, Mahdavi and Kalhaydari cultivars had Vrn-D1/Vrn-D1 genotype while Rakhshan had Vrn-D1a/Vrn-D1a genotype. Therefore, the hypothesis of pleiotropic effect was rejected and it was determined that the gene which is located at a close distance from Vrn-D1 is controlling the awns. The distance between these two genes is so tight that no crossing over has been occurred between them in 14 generations of sexual reproduction. Three known genes on chromosomes 4A, 5A and 6B are controlling awns. Yet, there is not known gene on chromosome 5D controlling awns. Therefore, the gene that is located at a short distance of Vrn-D1 and controls the awns has remained unknown till now. In this research, it was found that the awned phenotype is linked with the Vrn-D1a allele. Since awnless phenotype is not a desirable trait, the genetic linkage of these two genes reduces the agronomic value of cultivar.