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Measuring and predicting
change
in crop wild relative species
by Toby Hodgkin and Jozef Turok
International Plant Genetic Resources Institute (IPGRI), Rome, Italy
What is a crop wild relative?
• Self- and out-pollinating annuals• Grassland species• Temperate forest trees
(angiosperms, gymnosperms)• Weedy species• Rare, mountain endemic plants
Large variation in the characteristics…
• Distribution extent and pattern• Longevity• Life form• Habitat
Are crop wild relative species different
with respect to change, erosion and
pollution?
Pollution
• Substantial gene flow from cultivated
species to primary genepool species,
which are fully inter-fertile, occur
together and overlap in flowering
period• Examples: Hordeum spontaneum,
Oryza rupifogon, Teosinte,
Pennisetum, Beta maritima
Conservation objectives
• Conservation of the full amplitude of
variation within a species• Conservation of specific traits (frost or
drought resistance)
Change
• Erosion and genetic pollution
• Global changes of the environment
• Effects of the global climate change on
crop wild relative species
• Factors and processes of evolutionary
change
• Methods to assess change
Dispersal capability
• Depends on seed biology and vector
of dispersal
• For long-term survival of a species
under global climate change, the
dispersal capability must be greater
than the speed of environmental
change
Gene flow
Inter-population differentiation
Mu-ta-
tions
Natural selection
Genetic drift
Pheno-typic
plasti-city
Constraints
PromotersEriksson (2003)
Factors and processes of evolutionary change
• Natural selection
• Genetic drift
• Mutation
• Gene flow
• Mating system and recombination
• Phenotypic plasticity
Phenotypic plasticityChange of survival, %
20
10
0
–10
–20
–30
Latitudinal transfer
+3 +2 +1 0 –1 –2 –3 –4 –5
northwards southwards
Phenotypic plasticity
Norm of reaction
Eriksson (2003)
Indicators of change
Indicator taxa:• Utility value or known ecological significance• Existence value, for species under threat of extinction• Value for species known to be paradigms of a large
class of species
Indicators of genetic variation:• Easy to implement, based on good experimental
design, indicate processes and flows, give early warnings, have clear objectives
• Application of population genetics – conservation of the processes that maintain current genetic variation
Namkoong et al. (2002); McKenney et al. (1994)
Indicators of change
1. Number of sub-specific taxa2. Population size and physical location3. Environmental amplitude of populations4. Genetic diversity at marker loci within
individuals and populations5. Quantitative genetic variation6. Inter-population genetic structure7. Mating system
Brown et al. (1997)
Indicators of change
Criterion: Conservation of the processes that maintain genetic variation
1. Levels of genetic variation
2. Directional change in gene or genotype frequencies
3. Gene migration between populations
4. Reproductive processes/ mating system
Namkoong et al. (2002)
Gene flow
Raybould et al. (1996)
Genetic erosion
“The loss of genetic diversity, in a particular location and over a particular period of time, including the loss of individual genes (alleles), and the loss of particular combinations of genes such as those manifested in landraces or varieties. It is thus a function of change of genetic diversity over time.”
FAO (GDEV paper prepared for 9th Session of CGRFA, 2002)
Genetic erosion – measurement and monitoring
Characteristics of species populations
Population size
Large/ abundant
Small/ sparse
Geographic distribution
everywhere
local
Genetic pollution
• Exotic species (crops, forages and forest trees)
• Artificial hybrids (Populus, Brassica napus)
• Exotic provenances (crops, forages and forest trees)
• Artificially selected plants (mainly forest trees and forages)
• GMOs (mainly crops such as cotton, maize, Brassica, soybean relatives)
Potts et al. (2001)
Pollution – why does it matter?
• Loss or disruption of adaptive gene complexes
• Introduction of “domestication genes” and therefore loss of natural survival capacities
• Increase of susceptibility to pests• Loss of out-breeding characteristics (thus
inbreeding depression)• Vigor loss in hybrids• Increase in weedy habit
Genetically modified organisms
• Vigor and likelihood of out-crossing (e.g. through spread of crop to new areas)
• The genes themselves – herbicide resistance, pest resistance
• Disruption of pollinator and plant communities
Transgene escape
• Plant containing it persists after harvesting in an agricultural or disturbed habitat or invades a natural habitat
• Transgene is transferred by pollination to another crop which persists in an agricultural, disturbed or natural habitat
• Transgene is transferred by pollination to a related wild plant which persists in agricultural habitats, disturbed habitats or natural habitats
Raybould and Gray (1993)
Potential indicators
• Existence of crop wild relatives in area (numbers and relationships)
• Viability and fertility of progeny
• Breeding system and extent of synchrony of flowering; presence of pollinators
• Extent to which subsequent generations can remain fertile and backcross
• Migration selection balance for transgene
Gepts and Papa (2003)
Conclusions
• Sufficient genetic variation within species
• Criteria and indicators: baseline data to show trends
• Important measurements, methods
• Early warning
• Trans-national monitoring and policy advice