Genetic Mechanisms of Vernalization Requirement Duration in Winter Wheat Cultivars

Abstract

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.