Allele frequencies in the VRN-A1, VRN-B1 and VRN-D1 vernalization response and PPD-B1 and PPD-D1 photoperiod sensitivity genes, and their effects on heading in a diverse set of wheat cultivars (Triticum aestivum L.)

Heading of cereals is determined by complex genetic and environmental factors in which genes responsible for vernalization and photoperiod sensitivity play a decisive role. Our aim was to use diagnostic molecular markers to determine the main allele types in VRN - A1 , VRN - B1 , VRN - D1 , PPD - B1 and PPD - D1 in a worldwide wheat collection of 683 genotypes and to investigate the effect of these alleles on heading in the field. The dominant VRN - A1 , VRN - B1 and VRN - D1 alleles were present at a low frequency. The PPD - D1a photoperiod-insensitive allele was carried by 57 % of the cultivars and was most frequent in Asian and European cultivars. The PPD - B1 photoperiod-insensitive allele was carried by 22 % of the genotypes from Asia, America and Europe. Nine versions of the PPD - B1 -insensitive allele were identified based on gene copy number and intercopy structure. The allele compositions in PPD - D1 , PPD - B1 and VRN - D1 significantly influenced heading and together explained 37.5 % of the phenotypic variance. The role of gene model increased to 39.1 % when PPD - B1 intercopy structure was taken into account instead of overall PPD - B1 type (sensitive vs. insensitive). As a single component, PPD - D1 had the most important role (28.0 % of the phenotypic variance), followed by PPD - B1 (12.3 % for PPD - B1 _overall, and 15.1 % for PPD - B1 _intercopy) and VRN - D1 (2.2 %). Significant gene interactions were identified between the marker alleles within PPD - B1 and between VRN - D1 and the two PPD1 genes. The earliest heading genotypes were those with the photoperiod-insensitive allele in PPD - D1 and PPD - B1 , and with the spring allele for VRN - D1 and the winter alleles for VRN - A1 and VRN - B1 . This combination could only be detected in genotypes from Southern Europe and Asia. Late-heading genotypes had the sensitivity alleles for both PPD1 genes, regardless of the allelic composition of the VRN1 genes. There was a 10-day difference in heading between the earliest and latest groups under field conditions.