The Relationships between Development and Low Temperature Tolerance in Barley Near Isogenic Lines Differing for Flowering Behavior

Flowering time, vernalization requirement, photoperiod sensitivity and low temperature tolerance are key traits in the Triticeae. We characterized a set of isogenic genetic stocks-representing single and pairwise substitutions of spring alleles at the VRN-H1, VRN-H2 and VRN-H3 loci in a winter barley background-at the structural, functional and phenotypic levels. High density mapping with reference to the barley genome sequence confirmed that in all cases target VRN alleles were present in the near isogenic lines (NILs) and allowed estimates of introgression size (at the genetic and physical levels) and gene content. Expression data corroborated the structural and phenotypic results. The latter confirmed that substitution of a spring allele at any of the VRN loci is sufficient to eliminate vernalization requirement. There was no significant change in low temperature tolerance with substitution of a spring allele at VRN-H2, but there were significant losses in cold tolerance with substitutions at VRN-H1 and VRN-H3. Reductions in cold tolerance are ascribed to an accelerated transition from the vegetative to reproductive state. The set of NILs will be a rich resource for understanding the genetics of vernalization, low temperature tolerance and other traits encoded/regulated by genes within the introgressed intervals.