Genomic Constitutions Of Natural Hybrids Of Elymus From Hongyuan,Sichuan

Natural hybridization between different species and genera is frequently occurred in Triticeae.Elymus L.is a genus of polyploid with the St and H genomes.Elymus species have excellent forage traits and strong resistance characteristics.Most of Elymus species were used as forage with high quality.Ten natural hybrids of the Triticeae species were discovered in the field of Hongyuan,Sichuan,China.Morphologically,these hybrids are strong with 97-131 cm tall,tiller 98-361,perennial,and sterile or with very low fertility(0.13%).In order to investigate the genomic constitutions and the possible parental species of the 10 natural hybrids,different methods including karyotype,meiotic pairing behavior and genomic in situ hybridization(GISH)were used in this study.The main results were as follows:1.Morphologically,the hybrids looked stronger than the other plants in the field and looked like the Elymus species,e.g.spikelet 2 per node,lanceolate glumes,palea equal to lemma.Species co-occurring at the same locality with the hybrids were Elymus sib iricus,E.nutans,and some other species of Elymus.2.The number of chromosomes was observed in the metaphase of mitosis of the ten natural hybrids.The results showed that Eight hybrids(named SH01-08)were pentaploids(2n = 5x = 35),while two hybrids(named SH09,SH10)were tetraploids(2n = 4x = 28).3.Meiotic pairing was observed in the ten natural hybrids.Meiotic pairing averaged 7.90 to 10.93 bivalets per cell in the eight pentaploid hybrids.The results suggested that more than one(some were two)set of genome in the pentaploid hybrids were homology.Chromosome pairing of the two tetraploid hybrids was higher,with averaged 13.21 and 13.88 bivalents per cell,respectively.The results indicated that the two set of genomes in tetraploid hybrids were homology.4.GISH results showed that the eight contain 14 St chromosomes,14 H chromosomes and 7 Y chromosomes.Thus,the genomic constitutions of pentaploid hybrids is StStHHY.Meanwhile,chromosomal translocation between the 2H and 3Y genomes were observed in four pentaploid hybrids(SH01-SH04),but not observed of the other four pentaploid hybrids.The two tetraploid hybrids have 14 St chromosomes and 14 H chromosomes based on GISH analysis.Thus the genome constitutions of tetraploid hybrids is StStHH.5.Based on above results,it is concluded that the pentaploid hybrids contain the StStHHY genomes and might hybridize from species with tetraploids containing the StStHH genomes and pentaploids with the StStHHYY genomes;the two tetraploid hybrids possess the StStHH genomes and might come from the hybridization between Elymus species with the StStHH gonomes.The parental species of the natural hybrids needs further studies.