Evaluation of cold hardiness in two sets of near-isogenic lines of wheat (Triticum aestivum) with polymorphic vernalization alleles

In wheat, variation at the orthologus Vrn-1 loci, located on each of the three genomes, A, B and D, is responsible for vernalization response. A dominant Vrn-1a allele on any of the three wheat genomes results in spring habit and the presence of recessive Vrn-1b alleles on all three genomes results in winter habit. Two sets of near-isogenic lines (NILs) were evaluated for DNA polymorphisms at their Vrn-A1, B1 and D1 loci and for cold hardiness. Two winter wheat cultivars, 'Daws' and 'Wanser' were used as recurrent parents and 'Triple Dirk' NILs were used as donor parents for orthologous Vrn-1 alleles. The NILs were analysed using molecular markers specific for each allele. Only 26 of 32 'Daws' NILs and 23 of 32 'Wanser' NILs had a plant growth habit that corresponded to the marker genotype for the markers used. Freezing tests were conducted in growth chambers programmed to cool to -21.5 degrees C. Relative area under the death progress curve (AUDPC), with a maximum value of 100 was used as a measure of death due to freezing. The average relative AUDPC of the spring habit 'Daws'Vrn-A1a NILs was 86.15; significantly greater than the corresponding winter habit 'Daws'Vrn-A1b NILs (42.98). In contrast, all the 'Daws'Vrn-A1bVrn-B1aVrn-D1b and Vrn-A1bVrn-B1bVrn-D1a NILs (spring habit) had relative AUDPC values equal to those of their 'Daws' sister genotypes with Vrn-A1bVrn-B1bVrn-D1b NILs (winter habit). The average AUDPC of spring and winter habit 'Wanser' NILs differed at all three Vrn-A1, Vrn-B1 and Vrn-D1 locus comparisons. We conclude that 'Daws' and 'Wanser' have different background genetic interactions with the Vrn-1 loci influencing cold hardiness. The marker for Vrn-A1 is diagnostic for growth habit and cold hardiness but there is no relationship between the Vrn-B1 and Vrn-D1 markers and the cold tolerance of the NILs used in this study.