Distribution of the Vrn-D1b allele associated with facultative growth habit in Chinese wheat accessions

Vernalization requirement in wheat is determined by allelic variation mainly at three loci, Vrn-A1, Vrn-B1 and Vrn-D1. Up to 2011 only two alleles at the Vrn-D1 locus were known. The dominant allele, now designated as Vrn-D1a, confers spring growth habit, and the other, recessive allele, vrn-D1, is associated with the winter growth habit. Recently, we found an additional dominant allele, Vrn-D1b, associated with the facultative growth habit. As facultative wheat cultivars play an important role in wheat production we screened 689 accessions from all over China, with a specific aim of determining the frequency and distribution of Vrn-D1b. The results showed that Vrn-D1a, Vrn-D1b and vrn-D1 were present in 27.3, 20.6 and 52.1 % of all accessions, respectively. Vrn-D1a was mostly distributed in the autumn sown spring wheat zone, whereas Vrn-D1b was common in the autumn sown facultative wheat zone. One cultivar (Shiluan 02-1) was heterogeneous at the Vrn-D1 locus. A comparison between the Vrn-D1b genotype and the vrn-D1 genotype from the same cultivar showed that without vernalization the Vrn-D1b genotype reached the double ridge (DR) stage 27 days earlier than the vrn-D1 genotype. Vernalization responses, expressed as a reduction in the number of days to reach the DR stage following cold treatment, at 4 A degrees C for 20, 30 and 40 days, were 62, 67 and 75 days, respectively, for the Vrn-D1b genotype, and 74, 87 and 98 days, respectively, for the vrn-D1 genotype, confirming the effect of Vrn-D1b on facultative growth habit. Pedigree analysis indicates that the Vrn-D1b allele originated from Chinese landraces.