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

• Often long-lived perennials

• Widespread in agricultural and semi-natural landscapes

• Often outbreeding with high levels of heterozygosity

• 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

• 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

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

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

Initial evaluation under cutting

Compared with control of same leaf size

Four best lines selected

Ac 4162

Ac 4164

Ac 4174

Ac 4179

Further evaluation under grazing

Best line identified

200 plants evaluated as

spaced plants

17 best plants

selected

Evaluated under

continuous sheep grazing

in 2003

Evaluation under continuous sheep grazing

Clover D.M. Yield Kgha-1

2nd year 3rd year

Ac 4162 1415 788

Ac 4164 1944 1473

Ac 4174 2271 1681

Ac 4179 2424 1850

S184 3176 2924

Menna 2902 1458

Selection line

Control

Selection line evaluated under continuous sheep grazing

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

• 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

• 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

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

• In situ conservation of :T. ambiguumT. 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’

• 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 (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

• 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

• Comparison of modern varieties and old varieties/landraces

• Invertebrate counts at 3 N levels

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

• 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