Genetic erosion and genetic pollution in forage species and their wild relatives
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Genetic erosion and genetic ‘pollution’ in forage species and their wild relatives. Michael T. Abberton Legume Breeding and Genetics Team Institute of Grassland and Environmental Research John M. Warren Institute of Rural Sciences University of Wales Aberystwyth, Ceredigion, Wales, UK.

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Genetic erosion and genetic ‘pollution’ in forage species and their wild relatives.

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Genetic erosion and genetic pollution in forage species and their wild relatives

Genetic erosion and genetic ‘pollution’ in forage species and their wild relatives.

Michael T. Abberton

Legume Breeding and Genetics Team

Institute of Grassland and Environmental Research

John M. Warren

Institute of Rural Sciences

University of Wales

Aberystwyth, Ceredigion, Wales, UK


Forage species

Forage species

  • Often long-lived perennials

  • Widespread in agricultural and semi-natural landscapes

  • Often outbreeding with high levels of heterozygosity


Genetic erosion and genetic pollution in forage species and their wild relatives

  • Recruitment from seed is at a low level

  • Vegetative spread may result in dominance of a few clones

  • Hybridisation with ‘wild’ relatives can occur-likely to be at low levels in some cases (e.g. Trifoliums, ryegrass/fescue) more in others (e.g. perennial ryegrass/Italian ryegrass)


Genetic erosion

Genetic Erosion

  • Major threat is loss of habitat

  • Within species erosion likely to be significant for future breeding

  • Loss of diversity in a few wild relative species may be important


Using germplasm from sites of potential genetic erosion

Using germplasm from sites of potential genetic erosion

Collecting trips to Bulgaria, former

Czechoslovakia and Poland

Anticipated changes in management

Expected that traditional managements would

favour germplasm with traits for interest for future

varieties in UK


Genetic erosion and genetic pollution in forage species and their wild relatives

44 different lines from Poland characterised under field conditions as individual plants for

Leaf size

Height

Spread

Flowering date

Flowering density

Disease

Rooting

Tolerance to grazing

Winter damage

etc


Genetic erosion and genetic pollution in forage species and their wild relatives

Initial evaluation under cutting

Four best lines selected

Ac 4162

Ac 4164

Ac 4174

Ac 4179

Further evaluation under grazing

Compared with control of same leaf size


Genetic erosion and genetic pollution in forage species and their wild relatives

Evaluation under continuous sheep grazing

Clover D.M. Yield Kgha-1

2nd year3rd year

Ac 41621415 788

Ac 416419441473

Ac 417422711681

Ac 417924241850

S18431762924

Menna29021458

Best line identified

200 plants evaluated as spaced plants

Evaluated under continuous sheep grazing in 2003

17 best plants selected


Genetic erosion and genetic pollution in forage species and their wild relatives

Selection line evaluated under continuous sheep grazing

Control

Selection line


Wild relatives collected at sites

Wild relatives collected at sites

  • T. fragerifum (strawberry clover)

  • T. angustifolium (narrow clover)

  • T. vesiculosum (arrow leaf clover)

  • T. spadiceum (large brown clover)


Related species that can hybridise to white clover

Related species that can hybridise to white clover

  • T. ambiguum. Hybridises with extreme difficulty. Ovule culture. Important in breeding of white clover

  • T. nigrescens (putative ancestor). Hybridises easily but F1 is annual triploid. Important in breeding of white clover

  • T. occidentale (putative ancestor) Diploid

  • T. uniflorum Tetraploid. Hybridises with difficulty


Priorities for in situ conservation in the clovers

Priorities for in situ conservation in the clovers

  • T. fragiferum

  • T. repens

  • T. cherleri

  • T. hirtum

  • T. subterrranean

  • T. pratense

    Lamont et al Chapter 4 Plant Genetic Resources of Legumes in the

    Mediterranean Maxted and Bennett (eds) Kluwer 2001


White clover

White clover

Genetic exchange between crop to wild relative

unlikely to have significant impact:

(i) Few species will cross

(ii) Difficulty of hybridisation

(iii) Low fertility of F1


Genetic erosion and genetic pollution in forage species and their wild relatives

  • In situ conservation of :

    T. ambiguum

    T. nigrescens

    and of the immense genetic diversity within the

    species itself is high priority with respect to white

    clover breeding.

  • Some related species may become of

    greater agricultural significance in their own right.


Genetic pollution

Genetic ‘pollution’

  • Exchange between introduced varieties and semi-natural populations likely to be common

  • Exchange with related species less common and often resulting in hybrids of low fertility


Genetic exchange between introduced and semi natural grasses

Genetic exchange between introduced and semi-natural grasses

(Warren et al Heredity 81 556-562 1998)

  • Compared perennial ryegrass (Lolium perenne) and Agrostis curtisii (limited distribution in S. England) using isozymes

  • Differences in genetic structure: deficit of heterozygotes in L. perenne


Genetic erosion and genetic pollution in forage species and their wild relatives

  • Agrostis curtisii: adjacent populations more genetically similar.

  • Not the case for L. perenne

  • Evidence of gene flow from introduced varieties into semi- natural grasslands e.g. Romney Marsh in Kent, Aberystwyth on the west coast of Wales

  • No apparent major impact on ecology


Effects on other species

Effects on other species

  • Comparison of modern varieties and old varieties/landraces

  • Invertebrate counts at 3 N levels


Questions

Questions

  • Relationship between molecular diversity and diversity in important traits ?

  • Is hybridisation likely to upset clines of adaptive significance (e.g. cyanogenesis in white clover, keel colour polymorphism in Lotus corniculatus )?

  • Effects of hybrids (e.g. triploids) on conservation

  • Trait specific effects on fitness ?


Acknowledgements

Acknowledgements

  • Legume Breeding and Genetics Team, IGER: Huw Powell, Andy Williams, Athole Marshall

  • Department of Environment, Food and Rural Affairs

  • Biotechnological and Biological Sciences Research Council


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