Allelic Variations of Vernalization Loci are Responsible for Quantitative Variation of Vernalization Requirement in Barley

Growth habits of barley (Hordeum vulgare) are divided according to their flowering behaviors into two: winter and spring. On the basis of degree of cold treatment period (vernalization requirement), barley accessions are assigned into five grades (grade I & II; spring, grade III-V; winter) (Saisho et al. 2011). A large number of wild ancestors of domesticated barley, H. spontaneum, belong to winter growth habit (grade III - V). Acquisition of spring growth habit (grade I and II) provided by several mutations into three vernalization loci (sgh1/vrn1, Sgh2/VRN1 and/or Sgh3/VRN3) is considered one of the driving forces to expand barley cultivation into high and low latitude area in western regions or North Africa (Bothmer et al. 2003). In contrast, higher grades of winter growth habit (grades IV and V) were mainly discovered in East Asia, such as China, Korea and Japan. As the results of ANOVA using a recombinant inbred lines derived from the cross between ‘H602’ (grade III) and ‘Hayakiso 2’ (grade IV), variation of degree of vernalization requirement was partially explained by allelic variation of three vernalization genes. Comparison of expression patterns of the three vernalization genes among the parents during vernalization treatment would support the results of the ANOVA. These evidences suggest that allelic variations of the vernalization genes would be responsible not only for the qualitative variation of growth habit (spring or winter), but also for the quantitative variation of the degree of vernalization requirement.