Cytological And Agronomic Traits Of Newly Synthetic Hexaploid Wheat

Common wheat(Triticum aestivum L.) is allopolyhexaploid wheat composed of three diploid genomes A,B and D,which experienced two polyploidizations during its evolution. Tetraploid wheat T.turgidum L.(AABB,2n=4x=28) was formed in the first intercrossing between T.urartu(AA,2n=2x=14) and Aegilops speltoides(BB,2n=2x=14).Then, common wheat(Triticum aestivum L.,AABBDD,2n=6x=42) was formed by the second polyploidization after the intercrossing between T.turgidum L.and Ae.tauschii(paternal, DD,2n=2x=14) followed by chromosome doubling.It has been indicated that only few T. turgidum wheats and Ae.tauschii are involved in the evolution of common wheat. Compared with its donor species,the genetic diversity of common wheat declined sharply, which is so-called "the evolutionary bottleneck".Therefore,lots of genetic variations in tetraploid wheat and Ae.tauschii don't existed in common wheat.Synthetic hexaploid wheat can be produced by simulating the evolution of common wheat through the chromosome doubling of the hybrid between tetraploid wheat and Ae.tauschii.Synthetic hexaploid wheat is useful for breeder to overcome the "the evolutionary bottleneck" of common wheat.Cytological and agronomic traits of the first generation(S₁) in 23 synthetic hexaploid wheats,derived from the spontaneous chromosome doubling of the hybrids between Triticum turgidum ssp.dicoccoides,ssp.turgidum,ssp.durum and Aegilops tauschii,were observed in this study.There were significant variances on meiotic behaviours,largely depending on the female donor of tetraploid wheat(T.turgidum).Three synthetic hexaploid wheats derived from T.turgidum ssp.dicoccoides AS285 were very abnormal in meiosis,which may be related to the variation in Phl allele,responsible for the meiotic diploidization in wheat.The irregular meiosis may lead to the cytological instability of synthetic hexaploid wheat.Therefore,it is necessary to observe meiosis of newly synthetic hexaploid wheat in order to avoid the applications of synthetic hexaploid wheat with irregular meiosis in studies on genetics.Based on the present study,the number of univalents can be used as an indicator for the irregularity of meiosis.Moreover,there were high variations on agronomic traits in synthetic hexaploid wheat,thus indicating their value on wheat breeding.