Differential effects of Aegilops tauschii genotypes on maturing-time in synthetic hexaploid wheats

Bread wheat (Triticum aestivum) is a hexaploid species with A, B and D genomes. Therefore, most breadwheat genes are present in the genome as triplicated homoeologous genes (homoeologs) derived from the an-cestral A, B, and D genome diploid species. Maturing-time, which is associated with flowering-time and thegrain-filling period, is one of the most important agronomic traits for wheat breeding. Here, the effects ofhomoeologs derived from D genome diploid species on maturing-time in bread wheat were examined in syn-thetic hexaploid wheats obtained by crossing tetraploid durum wheat T. turgidum ssp. durum cv. Langdonand three accessions of the D genome diploid species (Aegilops tauschii). After vernalization, the synthetichexaploid wheat derived from an early-flowering D genome donor showed an early-flowering phenotypeamong the synthetic hexaploids, whereas the synthetic wheat derived from a late-flowering D genome donorwas late-flowering among the synthetic hexaploids. This suggests that the early-flowering phenotype inhexaploid wheat is affected by the homoeolog for early-flowering in the D genome donor. In contrast,maturing-time and grain-filling period in the synthetic hexaploids did not correspond with those of the Dgenome donors, suggesting that these traits are controlled by the interaction between homoeologs on the A,B and D genomes in hexaploid wheat.Key Words: maturing-time, grain-filling period, hexaploid, wheat, Triticum aestivum, Aegilops tauschii,homoeolog.IntroductionIn cereal crops such as wheat and barley, maturing-time,which includes flowering-time and the grain-filling period,is an important character because of its influence on adapt-ability to different environmental conditions. Bread wheat(Triticum aestivum, 2n=6x =42, genome constitutionAABBDD) is grown in a wide range of environments allover the world, and its wide adaptability results from thevariation in maturing-time among cultivars (reviewed inWorland and Snape 2001).Many genetic studies have been performed to investigatethe genetic control of heading/flowering-time in wheat andthree component factors have been identified: vernalizationrequirement, photoperiod sensitivity, and narrow-senseearliness (earliness per se) (Yasuda and Shimoyama 1965,reviewed in Murai et al. 2005). Vernalization requirement isconcerned with the sensitivity of the plant to cold tempera-ture for accelerating spike primordium formation. The ver-nalization insensitivity (spring habit) genes, Vrn-A1, Vrn-B1and Vrn-D1, have been shown to be located on chromo-somes 5A, 5B and 5D, respectively, of bread wheat. The Agenome of hexaploid bread wheat came from T. urartu, theB genome from Aegilops speltoides or another speciesclassified in the Sitopsis section, and the D genome fromAe. tauschii (Feldman 2001). As a consequence of itsorigin, the hexaploid wheat genome contains triplicatedhomoeologous genes (homoeologs) derived from the ances-tral diploid species. Vrn-A1, Vrn-B1 and Vrn-D1 are thehomoeologs of the Vrn-1 gene. Vrn-A1 of the diploideinkorn wheat T. monococcum (2n =2x =14, A