| Population structure is determined by the interaction between gene flow and genetic drift. It is well established that gene flow can be restricted by environmental barriers. Genetic drift can be intensified by stochastic processes which are known to interact with demographic characteristics.Gene flow can be transmitted by pollen and seeds. Roegneria ciliaris(Triticeae, Poaceae) is widely d istributed in C hina, Japan and the Russian Federation and has multiple origins. Based on cytological data, R. ciliaris and R. japonensis were combined into one species and named as R. ciliaris. R. shandongensis is distributed in China and eastern Asia and has close relationship with R. ciliaris. R. shandongensis is easily confused with Elymus tsukushiensis and can be distinguished from E. tsukushiensis by three major taxonomic characters. The hyaline margin is wanted in glumes and lemmas of R. shandongensis, but it is possessed by E. tsukushiensis(Salonom, 1990). Glumes of R. shandongensis are larger in length and more nerves(5–7 nerves) than E. tsukushiensis(3–5 nerves)(Salonom, 1990). The apex of glumes is acute in R. shandongensis, rather the apex of glumes is tapered or awned in E. tsukushiensis. Although R. ciliaris and R. shandongensis had different morphological characters, the two species include many genes that confer resistance to diseases and pests and provide useful gene pools for wheat and forage grass improvement.Recently, populations of the two species have been found to occur sympatrically in three islands(Tian-heng island, Zhu-cha island, and Ling-shan island), at shorelines next to curbs(Yang-kou shoreline and Yun-lu shoreline), and in maninland areas from Shandong Province. Results of field observations, indicating R. shandongensis has higher population densities in most regions except of Ling-shan island that is occupied by more R. ciliaris, suggest that the two species have differe nt demographic traits. After six years of observations, two obvious differences are found between the two species. O ne major difference between R. ciliaris and R. shandongensis is if seeds are dispersed or not after maturation. Most seeds of R. shandongensis stay enclosed in spikelets, while most seeds of R. ciliaris are shed around the plant individual. The other is if the surface of the seed sampled from the same region is dirty or not, i.e., if some black spots are found on the surface of the seed or not. The surface of the R. ciliaris seed is frequently covered with black spots, while the surface of the R. shandongensis is not so frequent dirty. Here, our aims were to quantify the population genetic diversities and differentiation of R. ciliaris and R. shandongensis and interpret these results in the light of interspecific differences in geographical isolation, seed dispersal and seed quality.Through research, the PCR reaction system of 20 u Lwas determined: 2.5mm10 × buffer(Mg2+ free) 2.0 u L, 2.5 mm Mg C l2 2.4 u L, 2.5 mm d NTP 1.6 u L, 50 ng of DNA, and 2 mmol / L primer 3.0 u L, 1 unit of Taq enzyme and sterile distilled water was added to 20 u L(the additive volume of 2.5mm Mg C l2 was adjusted according to different primers). The results of using this PCR system are as follow: 1) Variation of SSR markers suggested populations of R. ciliaris showed a similar diversity(0.39 – 0.57) with R. shandongensis(0.33 – 0.57). AMOVA indicated higher variation within populations(23%) of R. shandongensis as compared to the variation within populations(31%) of R. ciliaris. The high Fst in R. ciliaris indicated the effects of severe local fragmentation. The relatively low Fst in R. shandongensis implied extensive gene flow among populations and may suggest that such gene flow was promoted by seed- mediated transport due to human activities. The Mantel test failed to detect significant correlations between the genetic and geographic distances in either species. UPGMA clustering and PCo A analysis also showed that the R. shandongensis and R. ciliaris populations were grouped into three clusters without geographical clustering. 2) Variation of resistance-gene based markers(RGMs) linked to loci conferring resistance to barley yellow dwarf virus(BYDV, Ryd loci) suggested populations of R. ciliaris showed a remarkably lower diversity(0.10 – 0.15) than R. shandongensis(0.33 – 0.42). AMOVA indicated higher variation within populations(90%) of R. shandongensis as compared to the variation within populations(57%) of R. ciliaris. The high Φst and low genetic diversity in R. ciliaris indicated the effects of severe local fragmentation. The relatively low Φst and high genetic diversity in R. shandongensis implied extensive gene flow among populations and may suggest that such gene flow was promoted by seed- mediated transport due to human activities. The Mantel test failed to detect significant correlations between the genetic and geographic distances in either species. UPGMA clustering and PCo A analysis also showed that the R. shandongensis populations were grouped into one clusters without geographical clustering, and R. ciliaris populations were grouped into 3 clusters with clear geographical structuring. These results indicated genetic drift and gene flow made effect on the genetic diversity and differentiation of the two Roegneria species. Gene flow was benefited from the waters of their distributions, which has got wind and increased the pollen flow. Also, gene flow was benefit from the good quality of seeds. For example, R. shandongensis had more rate of gene flow than R. C iliaris due to its high seed quality. However, the more study is need to supply more detailed evidence. |
PDF Full Text Request