Genetic erosion and genetic ‘pollution’ in forage species and their wild relatives. Michael T....
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![Page 1: Genetic erosion and genetic ‘pollution’ in forage species and their wild relatives. Michael T. Abberton Legume Breeding and Genetics Team Institute of.](https://reader035.fdocuments.us/reader035/viewer/2022070401/56649f175503460f94c2e056/html5/thumbnails/1.jpg)
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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Forage species
• Often long-lived perennials
• Widespread in agricultural and semi-natural landscapes
• Often outbreeding with high levels of heterozygosity
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• 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)
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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
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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
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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
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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
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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
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Selection line
Control
Selection line evaluated under continuous sheep grazing
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Wild relatives collected at sites
• T. fragerifum (strawberry clover)
• T. angustifolium (narrow clover)
• T. vesiculosum (arrow leaf clover)
• T. spadiceum (large brown clover)
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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
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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
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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
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• 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.
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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
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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
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• 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
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Effects on other species
• Comparison of modern varieties and old varieties/landraces
• Invertebrate counts at 3 N levels
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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 ?
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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