Genetic Loci for Vernalization Requirement Duration in Winter Wheat
Abstract
Wheat is traditionally categorized into two classes, winter wheat and spring wheat. Winter wheat requires a period of low temperature to accelerate the transition from vegetative to reproductive development, 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. Winter wheat cultivars have various durations of vernalization requirements that can be manipulated to regulate the developmental process for different purposes in wheat production, but little is known about how this important trait is genetically controlled. In this study, two diploid winter wheat accessions, PI362553 and G3116 were found to require 2 weeks and 5 weeks of low temperature, respectively, to attain their vernalization saturation points. An F2 population was developed from a cross between these two accessions, and the population was treated with 2 weeks of low temperature in order to observe the most sufficient segregation in vernalization requirement duration. A total of 114 markers including 104 SSR markers transferred from hexaploid wheat and 10 PCR markers developed for 6 known flowering time genes and 4 RFLP loci were mapped in 94 lines of this population. A major QTL was located on the long arm of chromosome 7Am in a 21.8 cM region between two SSR markers Xwmc96 and Xbarc172, explaining 22.8% of phenotypic variation. This QTL, designated QVrd.osu.7Am, was not associated with orthologues of eitherTmVRN3 or TmVRT2, two known flowering time genes that were mapped on the same chromosome. Therefore, QVrd.osu.7Am locus should contain new gene(s) responsible for the vernalization requirement duration in diploid winter wheat. TmVRN2 but not other five flowering time genes (TmVRN1, TmVRN3, TmPPD1, TmGI, and TmVRT2) had a significant effect (P<0.05) on heading date in the vernalized population by statistical analysis, although a minor QTL associated with the TmVRN2 locus on chromosome 5Am did not reach the LOD value of 2.5 for a common threshold. Based on these findings, we conclude that vernalization requirement duration in the genetic background of the diploid wheat applied in this study is regulated by two QTLs, explaining part of the total phenotypic variation.
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- OSU Theses [15752]