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