| Triticeae is a tribe of about 350-450 species in Poaceae. The tribe occurs from temperate through subtropical to tropical regions. Many species in the tribe are of important economic values, most notably the wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rye (Secale cereale L.), and many important forage grasses (e. g., Elymus sibiricus L., Leymus chinensis (Trio.) Tzvelve. Some species are tolerant to enduring cold, draft and alkaline and thus are suitable for ecological restoration purposes. An understanding of the genetic and phylogenetic relationships with the tribe is crucial for wise use of the wild genetic resources.Due to natural hybridization between species of the same genus or even different genera and polyloidy, the taxonomy of the tribe Triticeae is still a big problem. The circumscription and relationships of the genera have been controversial topics for a long time without any consensus because of few samples of both species and genes. In this thesis, I sampled 61 species representing 27 diploid species and 34 polyploid species of 20 major basic genomes of all genera and used ten chloroplast regions (trnK-matK-trnK、 trnL-F、rbcL、psbK-trnS、psbA-trnK、petA-psbJ、ndhF-rpl32、ndhE-ndhG、 trnP-psaJ-rpl33、rpsl6-trnQ-psbK) and two single-copy nuclear genes (Accl and DMC1) to reconstruct the phylogeny, divergence times and biogeographic history of the main lineages of Triticeae. Here are some main results.1. Phylogenetic relationships of TriticeaeMultiple gene phylogenies indicate that (1) Psathyrostachys (Ns), Leymus (NsXm) and Hordelymus (Ns_) have a close relationship. Ns genome from Psathyrostachys served as a maternal donor for the formation of Hordelymus and Eurasian Leymus species; (2) Hordeum (H) and Stenostachys (HW) have a close relationship and the maternal parent of Stenostachys gracilis is Hordeum; (3) Most species in Hystrix has Xm and Ns genomes except the type species Hystrix patula which belongs to Elymus and the Xm genome is closely related to F (Eremopyrum) and P (Agropyron) genomes; (4) Eremopyrum (F) and Agropyron (P) have a common ancestor; similarly Australopyrum (W), Henrardia (O) and Peridictyon (Xp) have a common ancestor; (5) Aegilops and Triticum are non-monophyletic. They have a close relationship with Amblyopyrum, Taeniatherum (Ta), Crithopsis (K), Secale (R) and Heteranthelium (Q).2. The divergence times and biogeography of the main lineages in TriticeaeUsing relaxed molecular clock approach that we estimated that the tribe Triticeae started to diverge 24.3 million years ago (Mya) in the early Miocene. Two rapid evolution events were indicated. The first one is the origins of genera form 24.3Ma to 9.6Ma, and the second one is a radiation from 9.6Ma. The second repid evolution is perhaps triggered by inter-species hybridization which led to the formations of many henera of hybrid origins.Triticeae originated in Asia, most probably in eastern and central Asia. Hordelymus originated in east and central Asia. Elymus, Leymus and Pseudoroegneria spreaded to North America from Asia via the Bering Land Bridge.The ancestors of the Oceanian Australopyrum retrofractum and Stenostachys gracilis originated in Asia and the Mediterranean and spreaded to the Oceania by long distance dispersal after the collision of Australia-New Guinea plate and and the Asian plate in the middle Miocene. Another migration possibility is through the land bridge which connected Malaysia, Asia and Oceania during the Miocene glacial periods. Elymus rectisetus is more likely of a recent origin after a long distance dispersal of a species carrying Y genome.Aegilops, Agropyron, Eremopyrum and Triticum originated in central Asia or the Mediterranean region, but Lophopyrum (Ee) and Thinopyrum (Eb) are more likely of the Mediterranean region and Europe origins. Hordeum migrated from the Mediterranean area to the East Asia and there to North America through Berling land bridge, and then from North America to South America in the Pliocene. |
PDF Full Text Request