| Wheat, widely cultivated in the world, is a kind of plant in Poaceae and the second highest food crops. For a long time, people have been agained great progress in improving the yield and quality of wheat, however with the continuous deterioration of the ecological environment, such as plant pests, drought, barren, high salinity stress, which caused great losses of crops. Leymus Hochst. is a perennial gemus of grass in the Triticeae (Poaceae). All the species are polyploids with the chromosome numbers ranging from2n=4x=28to2n=12x=84. The genome of Leymus is NsXm, and they contain many excellent features:big spike, grain, pest-resistant, anti-sandstoms, rought and frost. Leymus is an important genetic resource and significant to the improvement of Triticeae cereal crops. However, the origin, definition, migration, geographical differentiation, presise taxonomic, ranks and relationships among the species of Leymus have been under discussion. In this study, we carried out phylogenetic analysis based on nrDNA ITS sequence and GISH analysis for seven Leymus species and its related species from seven diploid species in different genera in the Triticeae. The main results showed as follows:1. In the phylogenetic tree from ITS sequences, there was a direction in the process of evolution. The evolution direction of ITS sequence of L. racemosus, L. chinensis, L. triticoides, L. komarovii tend to Ns type, the evolution direction of ITS sequence of L. arenarius and L. angustus towards Ns and Xm type, but the evolution direction of ITS sequence of L. tianschanicus was inclined to Xm type. Therefore, the evolution direction of ITS sequence of different Leymus may be different.2. Genome DNA of Pseudoroegneria libanotica (2n=2x=14, St)was used as probe,while genome DNA of Psathyrostachy juncea(2n=2x=14, Ns) was used as blocking, in the genomic in situ hybridization with Leymus species.The results show that:1) Leymus arenarius (2n=4x=28),6chromosomes show yellow green fluorescence;2) Leymus chinensis (2n=4x=28),24chromosomes show yellow green fluorescence;3) Leymus angustus (2n=12x=84),4chromosomes show yellow green fluorescence;4) Leymus racemosus (2n=8x=56),1chromosomes show yellow green fluorescence. The results indicat that:there are some repetitive DNA homologous relationship between Xm genome of the Leymus species and St genome.3. Genome DNA of Eremopyrum triticeum (2n=2x=14, F) was used as probe,while genome DNA of Psathyrostachy juncea was used as blocking, in the genomic in situ hybridization with Leymus species.The results show that:1) L. arenarius, no chromosomes show yellow green fluorescence;2) Leymus triticoides (2n=4x=28), no chromosomes show yellow green fluorescence.The results indicat that:Xm genome of those two Leymus species have no-homology with the F genome.4. Genome DNA of Agropyron cristatum(2n=2x=14, P)was used as probe,while genome DNA of Psathyrostachy juncea was used as blocking, in the genomic in situ hybridization with L. arenarius,14chromosomes show yellow green fluorescence,The results indicat that there are some repetitive DNA homologous relationship between Xm genome of the L. arenarius and P genome.5. The DNA of Pse. libanotica (St), the DNA of Er. triticeum (F) and the DNA of Ag. cristatum (P) were used as probe respectively, the DNA of Psa. juncea (Ns) was used as the blocker, in the genomic in situ hybridization (GISH) with. L. komarovii, the chromosome of L. komarovii has no signal. But when Ns genome was used as probe, none of DN was used as blocker, the chromosomes showed yellow green fluorescence signal, indicating that the L. komarovii genome distantly related with the P, F, St genome and closely with the Ns genome, it is may be homologous tetraploid (NsNsNsNs).6. Combining ITS sequence analysis with GISH, Leymus often hybridize with the related species repeatly which caused interspecific introgression, just as P and St genome interogress into the genome of Leymus differently and involve in the polyploid origin of species in Leymus. |
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