Genetic Loci for Vernalization Requirement Duration in Winter Wheat.

Wheat is traditionally categorized into two classes, winter wheat and spring wheat. Winter wheat requires a period of low temperature to accelerate transition from vegetative to reproductive development and flowering, a phenomenon known as vernalization, whereas spring wheat has no vernalization requirement for flowering. The three vernalization genes, VRN1, VRN2 and VRN3, have been cloned, based on variation in vernalization requirement between spring and winter types of wheat and barley. However, little is known about how various vernalization requirements are genetically controlled among winter cultivars. Winter wheat cultivars are generally classified into three types: a weak winter type that is stimulated to flower by brief exposure of low temperature, a semi-winter type that requires 2 to 4 weeks of cold exposure for flowering, and a strong winter type requiring 6 to 8 weeks of cold exposure. Winter wheat occupies approximately 75% of total wheat in United States, and to understand genetic basis and molecular mechanisms of growth and development of winter wheat cultivars will be particularly important in keeping United Stated in the leading position in the world supply and exporter.
In this study, we generated an F₂ population from a cross between two types of winter wheat, the one requiring 2 weeks and the other requiring 5 weeks of low temperature to attain their vernalization saturation point. We have already mapped approximately 70 SSR markers in the segregating population. Flowering time of the still growing F₂ population plants has been segregated after the plants were treated with 2 weeks of vernalization, and it is expected that genes responsible for vernalization requirement duration could be located in linkage maps. This study was conducted in diploid wheat species T. monococcum (genome A^mA^m), in order to establish a simpler genetic model to explain variation in vernalization requirement duration in wheat.