| Leymus Hochst. is an important perennial genus of Triticeae Dumortier (Poaceae). There are about32species and19subspecies in Leymus, widely distributing in Eurasia and mountains of North America, and also a small amount of the distribution in South America. Many species of Leymus are not only main components of grass lands and grass marshlands, but also fine varieties of herbage and forage. Leymus species are mesoxerophytes, adapt to a quite broad range, from the warm temperate zone, temperate sylvosteppe to arid grasslands, desert grassland, steppe desert, and up to the elevations over4500meters also distributed. Most of Leymus species bear strong habitat adaptability in resistance to alkali and cold, drought tolerance, as well as such excellent characters as disease and insect resistance, bigger spikes and efficient photosynthesis, being an important genetic resource of cereal crop and forage in genetic improvement and germplasm breeding.However, the definition of the Leymus genus, precise taxonomic ranks, interspecific genetic relationships, NsXm genome composition and origin still have much divergence which are under discussion at present.In this study, genetic diversity, phylogenetic relationships and reticulate evolution analysis between polyploid Leymus species and their related diploid species as Psathyrostachys(Ns),Pseudoroegneria(St),Agropyron(P),Australopyrum(W),Hordeum(H), Lophopyrum(Ee), which were reconstructed based on intersimple sequence repeats (ISSR) molecular markers and chloroplast trnQ-rpsl6sequences, to evaluat the interspecific genetic relationships among Leymus and its relative genera, investigated the maternal donor of Ns genome and speculate the origins of Xm genome.The main results showed as following:1. The genetic diversity evaluat and phylogenetic relationships among41Leymus accessions representing22species and2subspecies, combined with Pseudoroegneria stipifolia, Psathyrostachys fragilis, Australopyrum retrofractum, Hordeum bogdanii, H. chilense and Lophopyrum elongatum were analyzed by using ISSR molecular markers.The data of ISSR bands were used to generate Nei’s similarity coefficients and to construct a dendrogram by means of UPGMA. The results showed as follows: (1) A total of376clear and reproducible DNA fragments were amplified by29ISSR primers, among which368(97.87%) fragments were found to be polymorphic,8-18polymorphic bands were amplified by each primer, with an average of12.69bands, which suggested that ISSR primers have abundant polymorphism in Leymus species and its relative genera.(2) The similarity coefficients data suggested great genetic diversity in genus Leymus and related diploid Triticeae species, the genetic diversity among the different species was more abundant than that of the different accessions.(3) L. hybrid, L. triticoides, L. ambiguous, L. salinus, L. innovatus and L. cinereus which come from North America were clustered with certain Leymus species come from central Asia and East Asia, suggesting closely relationship among them and speculating that their ancestor may come from central Asia.(4) L. duthiei was nested in the clade of Leymus species which indicated that L. duthiei is closely related to other Leymus species and supported it is included in genus Leymus.(5)40accessions of Leymus were clustered with Psa. fragilis in group I which suggested that Leymus species were closely relate to Psathyrostachys, giving strong evidence that Psathyrostachys is the maternal donorof Leymus species. Australopyrum retrofractum was clustered with partial Leymus species in Group I, infering that Xm genome of Leymus species was related to the W genome.2. Phylogenetic relationships and genetic genealogical of36accessions of Leymus representing25species, together with11diploid taxa from six monogenomic genusas Psathyrostachy(Ns), Pseudoroegneria(St), Agropyron(P), Australopyrum(W), Hordeum(H), Lophopyrum(Ee), which were analyzed via reconstructing phylogenetic tree and haplotype median-joining networks based on chloroplast trnQ-rpsl6gene sequences. The phylogenetic analyses by neighbor-joining and median-joining network analyses supported three major clades:Ns,St and Xm. Sequence diversity and genealogical analysis suggested that:(1) Leymus species from the same areas or neighboring geographic regions are closely related, partial Leymus species from Qinghai-Tibetan Plateau were clustered independently, suggesting that the trnQ-rpsl6gene of Leymus species from Qinghai-Tibetan Plateau and central Asia were evolutionarily distinct.(2) Leymus species from North America and Eurasia are evolutionarily distinct, yet partial of them were closely related to the Leymus species from central Asia, showing the geographical continuity of Leymus species in the process of evolution.(3) Most of the Eurasian Leymus species have obvious genetic relationship with Psathyrostachys, Psa. juncea serve as the Ns genome donor of Eurasian Leymus species, and there might be more than one Psathyrostachys species involved in the speciation of Leymus.(4)The Xm genome may be originated from ancestral lineage of Pseudoroegneria (St), Lophopyrum (Ee), Australopyrum (W) and Agropyron (P). |
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