Vernalization (VRN) and Photoperiod (PPD) Genes in Spring Hexaploid Wheat Landraces

Abstract

The heading time in wheat and some other cereals is mainly determined by the genetic system of VRN (vernalization response) and PPD (photoperiod response) genes. Using diagnostic DNA markers, we analyzed VRN-A1, VRN-B1, VRN-D1, and PPD-D1 allelic diversity in a set of landraces representing seven hexaploid spring wheat species from several regions of Eurasia. The determination of the spring growth habit was found to be variable: in 55.3% accessions, it was controlled monogenically by a VRN gene; in 30.3% accessions, by a combination of two VRN genes; and in 2.6% accessions, trigenically. The dominant Ppd-D1a allele was almost completely absent (only 2.6%) in the landraces, which suggests it being secondary to the recessive ppd-D1b allele as well as increase in its frequency during the recent “green revolution.” In species T. aestivum, Т. compactum, T. petropavlovskyi, and T. tibetanum, the Vrn-D1a frequency was shown to increase eastward with maximum concentration in the regions of Afghanistan, India, and China. In species with a compact ear (T. antiquorum, T. sphaerococcum, and Asian forms of Т. compactum), the spring growth habit is controlled by a single Vrn-B1a allele, which indicates their possible initial distribution in the same gene pool. The European and Asian T. spelta subspecies, despite the very fragmented distribution range, have the same Vrn-A1b and Vrn-B1c alleles, which genetically unites these subspecies. A common set of alleles of the VRN genes in landraces and modern cultivars have provided the adaptability of wheat to diverse environmental conditions during the long period of its cultivation. The newly detected DNA fragments in the first intron of VRN-D1 and PPD-D1 loci may mark new alleles and be of interest for further examination and use in breeding programs.