The Genetics of Winterhardiness in Barley: Perspectives from Genome-Wide Association Mapping

Fall-planted barley makes the best use of available precipitation in the Pacific Northwest of the United States. This growth habit is also suitable to many other areas of the world. A prerequisite for production in most of these areas is tolerance of low temperature during the vegetative growth stages. Fall-planted barley is often equated with winter habit barley. Winter habit type cereals require vernalization: a period of low temperature necessary to trigger the vegetative to reproductive transition. Facultative growth habit defines germplasm that is tolerant of low temperature but do not require vernalization. Cereals achieve their greatest cold tolerance during vegetative stages, and a vegetative condition can be maintained by vernalization sensitivity or sensitivity to short days. As global climate changes and temperatures fluctuate without warning, vernalization sensitivity becomes an unreliable trait for maintaining a vegetative condition, and thus maximizing cold tolerance. Hence the interest in short day sensitive facultative types -- provided that maximum cold tolerance can be achieved without vernalization sensitivity. Facultative cereals have the additional advantages that they can be fall or spring planted and they are amenable to rapid cycling breeding methods. In barley, winterhardiness loci have been identified using bi-parental QTL approaches. Candidates for the FR-H1 and FR-H2 QTL are VRN-H1 and a cluster of CBF family members respectively. VRN-H1, which interacts epistatically with VRN-H2 and VRN-H3, is also a major player in vernalization sensitivity. FR-H1 and FR-H2 are approximately 30 cM apart on the long arm of chromosome 5H. The candidate genes for the PPD-H1 and PPD-H2 photoperiod sensitivity QTL are HvPRR7 on chromosome 2H and HvFT3 on chromosome 1H respectively. Genome-wide association mapping provides a complementary or alternative approach to bi-parental mapping. In this research, we explored the genetics of winterhardiness in barley germplasm through genome-wide association mapping. We identified the same FR-H1, FR-H2, VRN-H2, PPD-H1 and PPD-H2 QTL identified via bi-parental QTL mapping. We found that FR-H1/FR-H2/VRN-H2 haplotypes predict maximum cold tolerant facultative germplasm with high certainty and that facultative germplasm is as cold tolerant as vernalization sensitive germplasm.