Genetic variation and geographical divergence in Elymus nutans Griseb. (Poaceae: Triticeae) from West China

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Abstract

Elymus nutans Griseb. as an important forage grass and gene pools for improving cereal crops, widely distributes in west China. However, little is known about its genetic and geographical patterns. Inter-simple sequence repeat (ISSR) markers were applied to assess genetic diversity and geographical divergence among 63 E. nutans accessions from west China. The cluster analysis separated the accessions into several groups with geographical origins. The molecular variance analysis (AMOVA) showed that the proportion of variance explained by within- and among-geographical group diversity was 43.2% and 56.8%, respectively. Based on pairwise genetic distances (ΦST) between geographical groups, the relationships were congruent with the cluster of accessions. The distinct geographical divergence of E. nutans was revealed between Qinghai-Tibet Plateau and Xinjiang. The ecogeographical conditions such as climate and mountain ranges and elevation behaved as the crucial factors for genetic divergence. Furthermore, the study also indicated that Qinghai-Tibet Plateau might be the diversity differentiation center of E. nutans. The result will facilitate the breeding program and germplasm collection and conservation.

Introduction

Genetic diversity as the basis for survival, adaption and evolution of species is ubiquitous in nature (Nevo and Beiles, 1989). However, patterns of genetic variation and the distribution of plant species are not uniform but structured in space and/or time, which are often affected by abiotic ecological factor, biotic agents and species characteristics (Frankel et al., 1995). At a small spatial scale, the microgeographical variation of plant species is usually attributable to species characteristics such as population sizes, breeding system, seed dispersal (Yan et al., 2009a). Conversely, across a wide geographical region, the ecological factor is the crucial factor causing the macrogeographical variation of plant species, which could be divided into different ecogeographical groups or ecotypes (Yahiaoui et al., 2008). Furthermore, the spatial structure of genetic variation of plant species is a prerequisite for effective management of conservation programs (Sun et al., 2001).

Elymus nutans Griseb. is a perennial, caespitose and allohexaploid (2n = 6x = 42) species in genus Elymus L., which contains the St, H and Y genomes (Lu, 1993). It is native to temperate and tropical Asia, ranging from western and central Asia in the west to China and Mongolia in the east, from Russia in the north to India and the Himalayas areas in the south (Clayton et al., 2006). It grows in grassland, among bushes, along river banks, on mountain slopes, and in swales, at altitudes from 1000 m up to 5000 m (Lu, 1993). In China, it distributes in north, northwest and southwest China, particularly on Qinghai-Tibet Plateau (Kuo, 1987). E. nutans is the valuable forage grass in the alpine regions and has the characters of resistance for cold, drought and pest that can be used to improve cereal crops, which plays an important role in the restoration of the disturbed grasslands and construction of artificial grasslands, as well as animal production (Chen and Jia, 2002).

Up to the present, there is limited knowledge regarding the genetic and geographical differentiation of E. nutans, limiting the utilization and conservation of resources (Yan et al., 2006, Ma et al., 2007). Yan et al., 2009a, Yan et al., 2009b studied the genetic variation of E. nutans and Elymus burchan-buddae (Nevski) Tzvelev at a small spatial scale, which revealed that altitude and seed dispersal were the crucial factors affecting the spatial structure of genetic variation. However, effective utilization and conservation of species depends largely on the amount of knowledge of patterns of genetic variation. In west China, there are complicated and diversified environmental conditions, including diverse climate, intricate landform and various soil types. Therefore, it is reasonable to hypothesize that there would be a high level of genetic differentiation among the regions. Here we conducted an analysis of the genetic diversity and spatial variation at a macroscale to test it.

ISSR uses simple sequence repeats anchored at the 5′ or 3′ end by a short arbitrary sequence as PCR primers (Zietkiewicz et al., 1994). ISSR marker is more reproducible than RAPD marker because of the longer SSR-based primers and allowing more stringent annealing temperature (Wolfe and Liston, 1998). Though ISSR technique has some shortcomings as a dominant marker, it has been proved as an effective tool for investigation of genetic variation of species and systematic, as well as population genetics (Reddy et al., 2002). The objectives of the present study were to evaluate genetic diversity of E. nutans from west China based on ISSR, and reveal the divergence patterns of this species at the macrogeographic scale.

Section snippets

Plant materials

A total of 63 E. nutans accessions from five provinces representing western regions of China were used in the study (Table 1, Fig. 1). They were obtained from the USDA-ARS, United States; Triticeae Research Institute, Sichuan Agricultural University, China; Sichuan Grassland Science Academy, China. The vouchers of the materials were deposited at the Department of grassland science, Sichuan agricultural university, China. Seeds with a pretreatment at a low temperature were germinated on

ISSR profiles

The 16 primers were applied for PCR amplification of 63 accessions, generated 349 reliable bands with sizes ranging from 200 to 2000 bp, of which 319 (91.40%) were polymorphic (Table 2). The number of scorable bands per primer ranged from 14 to 33, with an average of 21.81 bands, of which 19.94 were polymorphic. The PIC values ranged from 0.202 (U834) to 0.357 (U848) with a mean of 0.281. They also demonstrated the good discriminatory power of the markers identified (Table 2).

Genetic similarities and cluster analysis

The genetic

Discussion

In the present study, the high level of genetic polymorphism of E. nutans was detected by ISSR, which was similar to the previous result with gliadin (Ma et al., 2007). Among the different groups, Sichuan and Tibet groups had the highest genetic diversity, which could result from the complicated ecogeographical conditions of the regions and selected sample sizes (Zheng, 1996). Then, large variation within regions was revealed, which was mainly made up of the variation within geographical

Acknowledgements

The study was supported by The National Basic Research Program (973 Program) in China (No. 2007CB108907) and The National Nature Science Foundation of China (NSFC Grant No. 30871820). The authors thank USDA, Triticeae Research Institute of Sichuan Agricultural University and Sichuan Academy of Grassland Science for kindly supplying the seeds.

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