High SSR diversity but little differentiation between accessions of Nordic timothy (Phleum pratense L.)

O. Manninen,P. Tanhuanpää

doi:10.1111/j.1601-5223.2012.02244.x

Abstract

A large collection of genebank accessions of the hexaploid outcrossing forage grass species timothy (Phleum pratense L.) was for the first time analysed for SSR diversity on individual, population and regional level. Timothy is the most important forage grass species in the Nordic countries. Eighty-eight timothy accessions from Nordic countries and eight accessions around Europe were analysed with recently developed simple sequence repeat (SSR) markers. Timothy proved to be very polymorphic: the 13 selected SSRs amplified a total of 499 polymorphic alleles, the number of alleles per SSR locus varying from 15 to 74. Taking all SSR alleles together, the observed number in each accession ranged from 95 to 203. Levels of diversity were found to be significantly different between countries, vegetation zones and different cultivar types. However, the differentiation between accessions was low: most of the variation (94%) in the studied timothy material was due to variation within accessions and only 5% was between accessions and 1% between countries. Lack of geographical differentiation may reflect the outcrossing and hexaploid nature of timothy. Our results showed that neutral SSR markers are suitable for demonstrating levels of diversity but not alone adequate to resolve population structure in timothy. Nordic timothy material seems to be diverse enough for breeding purposes and no decline in the level of diversity was observed in varieties compared to wild timothy populations. Challenges in analysing SSR marker data in a hexaploid outcrosser were discussed.

Highlights

A large collection of genebank accessions of the hexaploid outcrossing forage grass species timothy (Phleum pratense L.) was for the first time analysed for simple sequence repeat (SSR) diversity on individual, population and regional level
The abundant centre model (Brown 1984) presumes reduced neutral genetic diversity within peripheral compared to more central populations (Eckert et al 2008)
Genetic diversity within and among 96 timothy accessions mostly from Nordic countries was assessed with 13 selected SSR loci

Summary

Introduction

A large collection of genebank accessions of the hexaploid outcrossing forage grass species timothy (Phleum pratense L.) was for the first time analysed for SSR diversity on individual, population and regional level. The distribution of hexaploid timothy covers most of Europe (Conert 1998), at the northern margin, namely northern boreal and alpine vegetation zones, harsh winter conditions may limit survival of timothy. This may be reflected in the levels of diversity. Characterisations were mostly made on coarse, relative scale and variation within each accession was not taken into account This data gives an overall picture of the phenotypic variation present in the collection. It doesn’t fully describe the levels of genetic diversity, the genetic structure of variation between and among populations nor the genetic distances between individuals or populations

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Conclusion