Allele frequency of VRN1 and Rht genes in historical lines
According to the frost trial results, except for VrnB1a , the mutated VrnA1a , VrnD1a and Rht alleles were highly associated with the frost QTL. It is interesting to see the allele frequency of these mutated genes in historical varieties. In the current study, a set of 171 commercial wheat cultivars, released between 1890 to 2015, were surveyed for the VRN1 and Rht allele frequencies. For VRN1 and Rht , recessive alleles made up 95-100% of varieties released before 1967, except for vrnB1(15%) (Fig. 9). After 1968, VrnA1a was maintained at around 61% whereas VrnB1a dropped from 85 to 50% and remained at that level thereafter. The VrnD1a allele appeared mainly in the varieties released after 2000. The Rht1 allele was presented in a large proportion of varieties released after 1968 (56-69% of lines) while theRht2 allele gradually increased to near 41% in recent years.