Studies On Systematics And Evolution Of Leymus (Poaceae: Triticeae)

Leymus Hochst. is an important perennial genus of Triticeae Dumortier (Poaceae). It includes about 30 species and 19 subspecies. They are distributed in the coastal areas of North Sea, Central Asia, East Asia, extending to Alaska and the western areas of North America. They are found in particularly large numbers on the mountains of Central Asia and North America. Formerly, it included about 10 species recorded in China. In addition to some new taxon reported in recent years, it includes about 25 species, 4 subspecies and 3 varieties, which are mainly distributed in north-western, north, north-eastern and south-western regions in China. Many species of Leymus are not only main components of grasslands and grass marshlands, but also fine varieties of herbage and forge. Growing in saline or alkaline lands, and dry or semi-dry areas, some species are highly adaptable to coldness, dryness and saline or alkaline lands. And some species bear such desirable traits as disease and insect resistance, bigger spikes, more and bigger grains and efficient photosynthesis. Being an important genetic resource, Leymus is of significance to improvement of Triticeae cereal crops. However, the origin and definition of the genus, precise taxonomic ranks and relationships among the species in the genus have been under discussion. The study on genetic diversity of Leymus would provide theoretical foundation for using this genus plants to breed Triticeae crops and herbage. The present study systematically evaluated the genetic diversity of Leymus on morphology, anatomy, cytology, biochemistry and molecular level, and investigated biosystematic relationships among species and evolution level in this genus as well. The main results showed as following:1. The 23 morphological characters comparison among the 18 taxon in Leymus showed that there existed distinct morphological variation in Leymus. L. arenarius (L.) Hochst., L. racemosus (Lam.) Tzvel., L. ovatus (Trin.) Tzvel., L. crassiusculus L. B. Cai and L. pseudaracermosus C. Yen & J. L. Yang belonged to Sect. Leymus of Leymus Hocsh., while L. multicaulis (Kar. & Kir.) Tzvel., L. chinensis (Trin.)Tzvel., L. aemulans (Nevski) Tzvel. and L ruoqiangensis S. L. Lu et Y. H. Wu were included in Sect. Anisopyrum (Griseb.) Tzvel., and L. secalinus (Georgi) Tzvel., L. secalinus var. tenuis L. B. Cai, L. paboanus (Claus) Pilg., L. angustus (Trin.) Pilg. and L. karelinii (Turcz.) Tzvel., L. tianshanicus (Drobow) Tzvel., L. flexus L. B. Cai, L. latiglumus L. B. Cai and L. aristiglumus L. B. Cai were categorized in Sect. Aphanoneuron (Nevski) Tzvel.. Morphological evidences indicated that the Sect. Leymus Hocsh. of Leymus Hocsh. is a relatively primitive section, whereas the Sect. Anisopyrum (Griseb.) Tzvel. is an advanced section.2. The endosperm cells of 21 species of Leymus were surveyed. The results showed that there existed distinct variation in endosperm cells of Leymus species. Different species had different endosperm cells. The significant variations were mainly included differences in the sizes, forms and quantity of endosperm cells. The characters of endosperm cells may be used to distinguish the species in Leymus. L. arenarius (L.) Hochst., L. racemosus (Lam.) Tzvel. and L. mollis (Trin.) Kara belonged to relatively primitive Sect. Leymus Hochst., with bigger endosperm cells than those of L. multicaulis (Kar. & Kir.) Tzvel. and L cinereus (Scribn. & Merr.) A. Love, which belonged to relatively advanced Sect. Anisopyrum (Griseb.) Tzvel..3. The karyotypes of 19 species and 1 subspecies in Leymus Hochst. were reported. The karyotype formulae were as follows: L. akmolinensis (Drobow) Tzvel., 2n=4x=28=20m(2SAT)+8sm(2SAT); L arenarius (L.) Hochst., 2n=4x=28=18m+4sm+ 6st(4SAT); L cinereus (Scribn. & Merr.) A. Love, 2n=4x=28=22m(2SAT)+6sm(4SAT); L condensatus (J. Presl) A. Love, 2n=4x=28=22m+4sm(2SAT)+2st(2SAT); L innovatus (Beal) Pilg., 2n=4x=28=24m(4SAT)+4sm(2SAT); L. hybrid, 2n=4x=28= 24m+4sm; L multicaulis (Kar. & Kir.) Tzvel., 2n=4x=28=20m+6sm+2st (2SAT)...