Allelic Variations in Phenology Genes in Club Wheat (Triticum compactum) and Their Association with Heading Date

Abstract

The allelic diversity within genes controlling the vernalization requirement (VRN1) and photoperiod response (PPD1) determines the ability of wheat to adapt to a wide range of environmental conditions and influences grain yield. In this study, allelic variations at the VRN-A1, VRN-B1, VRN-D1 and PPD-D1 genes were studied for 89 accessions of Triticum compactum from different eco-geographical regions of the world. The collection was evaluated for heading date in both field and greenhouse experiments under a long photoperiod and without vernalization. Based on heading date characteristics, 52 (58.4%) of the genotypes had a spring growth habit, and all of them carried at least one dominant VRN1 allele, while 37 (41.6%) accessions had a winter growth habit and carried the triple recessive allele combination. The photoperiod-sensitive Ppd-D1b allele was detected in 85 (95.5%) accessions and the insensitive Ppd-D1a allele in four (4.5%) accessions. A total of 10 phenology gene profiles (haplotypes) were observed at four major genes in the T. compactum germplasm collection. The LSD test revealed significant differences in the mean heading date among the different spring phenology gene profiles, both in greenhouse and field conditions. In addition, 21 microsatellite markers (simple sequence repeats, SSRs) were used to assess the genetic diversity in the collection. The 21 SSR markers amplified a total of 183 alleles across all the genotypes, with a mean of 3.2 alleles per locus. The polymorphic information content ranged from 0.49 to 0.94, with a mean of 0.84. The results of this study may be useful for both T. compactum and common wheat breeding programs as a source of agronomic traits.

Keywords: Triticum compactum; club wheat; flowering date; genetic variability; photoperiod; vernalization.

Figure 1

PCR amplification using allele-specific primers for VRN-A1, VRN-B1, VRN-D1 and PPD-D1 loci of different T. compactum genotypes. (a) Primers VRN1-AF and VRN1-INT1R to detect dominant Vrn-A1a and Vrn-A1b and recessive vrn-A1 alleles of the VRN-A1 gene; (b) MspI restriction patterns of the corresponding PCR products in Figure 1a, separated by polyacrylamide gels; (c) primers Intr1/B/F, Intr1/B/R3 and Intr1/B/R4 to detect Vrn-B1a, Vrn-B1b and vrn-B1 alleles of the VRN-B1 gene; (d) primers Intr1/D/F, Intr1/D/R3 and Intr1/D/R4 to detect Vrn-D1a, Vrn-D1s and vrn-D1 alleles of the VRN-D1 gene; (e) primers Ppd-D1-F, Ppd-D1-R1 and Ppd-D1-R2 to detect dominant Ppd-D1a photoperiod-insensitive and recessive Ppd-D1b photoperiod-sensitive alleles of the PPD-D1 gene. Common wheat cultivars Chinese Spring (CS), Mara, Cadet and Escacena were used as controls.

Figure 2

Allele frequencies in the VRN-A1, VRN-B1, VRN-D1 and PPD-D1 genes in the T. compactum collection.

Figure 3

Distribution of the different combinations of vernalization and photoperiod alleles (haplotypes) in a T. compactum germplasm collection by geographical origin.

Figure 4

Unweighted pair group method with arithmetic mean dendrogram obtained from cluster analysis of 89 T. compactum accessions based on the Dice similarity coefficient using 21 SSR markers.

Figure 5

Spike and seed morphology of different T. compactum accessions. From left to right: (a) PI 25970; (b) PI 60740; (c) PI 164160; (d) PI 191542; (e) PI 294567 and (f) PI 330540.