ALLELIC VARIATION OF HEADING-TRAIT-RELATED GENES, ESSENTIAL FOR WIDE ADAPTATION OF WHEAT, AND ITS APPLICATION TO WHEAT BREEDING

摘要

Heading time is a complex character controlled by narrow-sense earliness and modified by vernalization requirement and photoperiod response. In the mid-latitude regions, which include Japan, photoperiod response and narrow-sense earliness are equally important for the control of heading time of winter wheat, and vernalization requirement is important for adaptation to winter cold. This review has summarized the genetic basis of heading traits of wheat and the molecular diversity of the Vrn genes for vernalization response. The potential practical use of new alleles identified by molecular analysis is discussed. The difference between spring and winter ecotypes is caused by allelic differences in five homoeologous genes, Vrn-1 to Vrn-5. Among these, vrn-A2 is a recessive gene for spring growth habit, but the others are dominant. By a map-based approach, Vrn-1, Vrn-2, and Vrn-3 have been cloned. Allelic variation of Vrn-A1 was surveyed in 250 landraces of common wheat and 19 accessions of tetraploid wheat. The Vrn-A1 sequence of winter type landraces was identical to that of winter type accessions of T. monococcum. In contrast, four types of sequence variation were identified in spring type landraces of common wheat: Vrn-A1a, with an insertion of 140 bp; Vrn-A1b, with a deletion of 20 bp; Vrn-A1c, without In/Dels (identical to vrn-A1 allele); and an insertion of 124 bp.