The Cytological Basis Of Preferential Elimination Of D-genome Chromosomes In Progenies Between Synthetic Wheat And Rye

Triticale?x Triticosecale Wittmack?is the first manmade crop.Due to their better meiotic stability and fertility,hexaploid triticales have attracted more and more attention compared with octoploid triticales.In our previous study,hexaploids triticale were obtained from the hybrids between synthetic wheat and rye by fertility selection over several generation.Hexaploids can be found at the F₃ generation resulted frompreferential elimination of the D-genome chromosomes.However,the cytological mechanism of hexploid triticale production was still unknown.In the present study,we try to uncover the underlying cytological basis by study the variation of D-genome chromosomes in the hybrids between synthetic wheat and rye from the F₂ and F₃ generation.The main results are as follows:?1?The number of D-genome chromosomes ranged from five to fourteen among the analyzed 89 F₂ individuals.The highest three frequencies were fourteen?56.2%,50/89?,seven?20.2%,18/89?and thirteen?12.4%,11/89?.According to the distribution of D-genome chromosomes,the F₂s were divided into two distinct types.Type I contained 69individuals and their total chromosomes was around 56,with 10 or more from D-genome;Type II contained 19 individuals and their total chromosome was around 49,Type II contained 19 individuals and their total chromosome was around 49,with seven or less from D-genome.?2?All of the checked F₂s had at least one copy of chromosome 2D;except for726-7-7?with single copy of 2D,3D,5D,6D,and 7D?,all F₂s contained at least one complete set of D-genome chromosomes.All type I F₂s with 14 D-genome chromosomes contained two complete set of D-genome chromosomes?1-7D?;except for chromosome 2D,1D and 3-7D were randomly eliminated.Except for 726-7-7,each of the remaining seventeen type II F₂s contained a complete copy of 1-7D chromosomes.These results suggested the D-genome chromosome composition of F₂s was affected by some unknown selection pressures.III?3?All of the eight F₂s,derived from the synthetic wheat using Aegilops strangulata as the D-genome donor,were belonged to type I.However,the 80 F₂s,which derived from the synthetic wheat using Aegilops tauschii as the D-genome donor,belonged to both type I?61,76%?and type II?19,24%?,respectively.?4?Using synthetic wheat-rye hybrid F₁ as the female parent,Chinese spring as the male parent,we obtained five hybrids.Of these,two plants contained a complete set of D-genome chromosomes inherited from synthetic wheat,and the other three only contained three to five D-genome chromosomes.However,all of them retained chromosome 2D.?5?The chromosome constitution of F₃s,derived from three F₂s containing one complete copy of D-genome chromosomes and two F₂s containing twelve D-genome chromosomes,were analyzed.The former contained 15F₃s with an average of 2.2D-genome chromosomes,ranged from zero to five.The latter contained 13 F₃s with an average of 12 D-genome chromosomes,ranged from nine to fourteen.