Genetic Mechanisms of Vernalization Requirement Duration in Winter Wheat Cultivars

Wheat is cultivated across more land area than any other grain crops. Wheat cultivars are classified as two general types: winter wheat with variable low temperature requirement for a proper flowering time (vernalization) and spring wheat without the requirement, based on their qualitative vernalization requirement. Winter wheat cultivars are classified as three types, weak winter, semi-winter and strong winter, according to their quantitative vernalization requirement to reach a vernalization saturation point or achieve the maximum vernalization effect. Three vernalization genes, VRN1, VRN2, and VRN3, were cloned using a positional cloning approach and a one-gene model of qualitative variation in vernalization requirement between spring and winter wheat. A major gene for the vernalization requirement duration in winter wheat was mapped using a population of recombinant inbred lines (RILs) that were generated from two winter wheat cultivars, ‘Jagger’ and ‘2174’. Furthermore, the cloning population was developed using a RIL to backcross with 2174, which was segregated in a 3:1 ratio of the early flowered plants and the late flowered plants after the population was vernalized for 3 weeks. The wild type Jagger vrn-A1a allele for less vernalization was dominant over the 2174 vrn-A1b allele for more vernalization, and the two alleles encoded the vrn-A1 proteins with two point mutations. A third haplotype with one of the point mutations was found in common wheat. Gene markers were developed to direct breeding of semi-winter and strong winter wheat cultivars to adapt to different geographical areas and changing climates.