Phylogenetic analysis of Elymus (Poaceae) in western China.

Elymus L. is often planted in temperate and subtropical regions as forage. Species in the genus have 5 allopolyploid genomes that are found in the grass tribe Triticeae. To determine the phylogenetic relationships in Elymus species from western China, we estimated phylogenetic trees using sequences from the nuclear ribosomal internal transcribed spacer and non-coding chloroplast DNA sequences from 56 accessions (871 samples) of 9 polyploid Elymus species and 42 accessions from GenBank. Tetraploid and hexaploid Elymus species from western China had independent origins, and Elymus species from the same area or neighboring geographic regions were the most closely related. Based on the phylogenetic tree topology, the St- and Y-genomes were not derived from the same donor and Y-genome likely originated from the H-genome of Hordeum species, or they shared the same origin or underwent introgression. The maternal genome of tetraploid and hexaploid Elymus species originated from species of Hordeum or Pseudoroegneria. Additionally, Elymus species in western China began diverging 17-8.5 million years ago, during a period of increased aridification as a consequence of the Messinian salinity crisis. Elymus species adapted to drought and high salinity may have developed based on the environmental conditions during this period. Elymus evolution in western China may have been affected by the uplift of the Qinghai-Tibetan Plateau (5 million years ago), when Elymus seeds were dispersed by gravity or wind into a newly heterogeneous habitat, resulting in isolation.

Breaking dormancy in freshly matured seeds of Elymus sibiricus, an important forage grass in the Tibetan Plateau.

Elymus sibiricus L. is an important forage grass widely distributed in Asia and is usually a dominant species on Tibetan Plateau alpine grasslands. Here, we used the seed development indices of 1000 seed weight, seed moisture content, and seed viability to compare the seed characteristics at 10, 20, 30, 40, 50, and 60 days after anthesis (DAA) in five populations of E. sibiricus growing in Gannan, China. Additionally, seeds collected at 60 DAA were air-dried for one month, and the primary germination percentage (GP) was determined in the laboratory. Treatment of seeds with 0.2% KNO3, 100 mg/L cytokinin, and 500 mg/L GA3 were tested for their effects on dormancy. A primary GP of 16% was found after 12 d of 15/25°C incubation, with no differences among the five populations. The 1000 seed weight and seed viability steadily increased and moisture content continuously fell with DAA. The optimal harvest time for E. sibiricus in an alpine pasture was 50 DAA. No effect on dormancy was found after treating seeds with 0.2% KNO3 or 100 mg/L cytokinin; however, a low concentration of GA3 induced a prompt and synchronized germination. Freshly matured E. sibiricus seeds were classified to be in non-deep physiologically dormant. Treatment of seeds with GA3 before sowing enhanced the emergence speed and seedling uniformity in E. sibiricus.

RAPD analysis of genetic diversity and population structure of Elymus sibiricus (Poaceae) native to the southeastern Qinghai-Tibet Plateau, China.

Genetic diversity of Elymus sibiricus (Poaceae) was examined in eight populations from the southeast Qinghai-Tibet Plateau. We detected 291 RAPD polymorphic loci in 93 samples. The percentage of polymorphic bands (PPB) was 79%. Genetic diversity (H(E)) was 0.264, effective number of alleles (N(E)) was 1.444, Shannon's information index (H(O)) was 0.398, and expected Bayesian heterozygosity (H(B)) was 0.371. At the population level, PPB = 51%, N(E) = 1.306, H(E) = 0.176, I = 0.263, and H(B) = 0.247. A high level of genetic differentiation was detected based on Nei's genetic diversity analysis (G(ST) = 32.0%), Shannon's index analysis (33.7%), and the Bayesian method (θ(B) = 33.5%). The partitioning of molecular variance by AMOVA demonstrated significant genetic differentiation within populations (60%) and among populations (40%). The average number of individuals exchanged between populations per generation (N(m)) was 1.06. The populations were found to share high levels of genetic identity. No significant correlation was found between geographic distance and pairwise genetic distance (r = 0.7539, P = 0.9996). Correlation analysis revealed a significant correlation (r = 0.762) between RAPD H(E) found in this study and ISSR H(E) values from a previous study.

Origin of the H genome in StH-genomic Elymus species based on the single-copy nuclear gene DMC1.

Previous studies have suggested that the H haplome in Elymus could originate from different diploid Hordeum species, however, which diploid species best represent the parental species remains unanswered. The focus of this study seeks to pinpoint the origin of the H genome in Elymus. Allopolyploid Elymus species that contain the StH genome were analyzed together with diploid Hordeum species and a broad sample of diploid genera in the tribe Triticeae using DMC1 sequences. Both parsimony and maximum likelihood analyses well separated the American Hordeum species, except Hordeum brachyantherum subsp. californicum, from the H genome of polyploid Elymus species. The Elymus H-genomic sequences were formed into different groups. Our data suggested that the American Horedeum species, except H. brachyantherum subsp. californicum, are not the H-genomic donor to the Elymus species. Hordeum brevisubulatum subsp. violaceum was the progenitor species to Elymus virescens, Elymus confusus, Elymus lanceolatus, Elymus wawawaiensis, and Elymus caninus. Furthermore, North American H. brachyantherum subsp. californicum was a progenitor of the H genome to Elymus hystrix and Elymus cordilleranus. The H genomes in Elymus canadensis, Elymus sibiricus, and Elymus multisetus were highly differentiated from the H genome in Hordeum and other Elymus species. The H genome in both North American and Eurasian Elymus species was contributed by different Hordeum species.