Detecting gene flow from gm crops to wild relatives Mike Wilkinson



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Detecting gene flow from GM crops to wild relatives

  • Mike Wilkinson




In the United Kingdom

  • Of 30 crops reviewed

  • 7 have no cross-compatible wild relatives

  • 11with the potential for hybrid formation

  • 12 with a history of hybridization

  • From Raybould and Gray, 1993, amended by Wilkinson 2002



In the United Kingdom

  • First wave of GM crops

  • Maize No relatives

  • Oilseed rape Many relatives

  • Sugar beet 1 close relative

  • Potato 3 relatives, none compatible



The process of transgene recruitment and spread

  • Initial Hybridization

  • Introgression

  • Gene flow between populations

  • Changed fitness leading to change in population size, density or distribution

  • Effects on other organisms

    • Bilateral interactions(e.g. bitrophic)
    • Trilateral interactions (Tritrophic)
  • Changed community



Initial hybridization



Why quantify hybridization?



1. Hybrid frequency affects the likelihood of all subsequent consequences







2. Hybrid abundance dictate the value of measures to repress/prevent hybrid formation

  • Isolation distance

  • Male sterility

  • Integration site

  • Chloroplast transformation

  • Inducible promotors/ ‘terminator technology’

  • Transgene excision



Estimates of hybrid abundance and other exposure terms have most value for regulation when applied at national scale



How do you estimate F1 hybrid formation between crop and wild relatives across the UK?

  • Identify recipients

  • Quantify ‘local’ gene flow rates

  • Estimate long-range gene flow

  • Combine 1-3 to estimate frequency and location of hybrids





Possible primary recipients Scheffler & Dale (1994) Transgenic Res. 3, 263-278

  • Brassica rapa

  • B. oleracea

  • B. carinata

  • B. juncea

  • B. nigra

  • B. adpressa



Brassica rapa





Hybrid seed formation

  • 9-93% of seeds from B. rapa are hybrids

  • Average 60%

  • Surely lots of hybrids will be everywhere

  • Jorgensen and Andersen (1994)



No, because





Hybrid survival

  • Hybrid seeds show <10% dormancy

  • Weedy B. rapa shows 60-90% dormancy

  • So in next year, 90% of hybrids germinate but only 10-40% of B. rapa

  • WEED CONTROL IS EFECTIVE IN CEREALS

  • Linder (1998) Ecological Applications 8 (4): 1180-1195





Wild B. rapa

  • Local hybrids

  • Long-range hybrids





Screen seed offspring for hybrids

  • 15341 seeds sown from two populations

  • 8647 seeds germinated

  • 46 hybrids [morphology, flow cytometry, chromosome counts, ISSR] (0.5%)

  • Hambledon (5m separation- 0.4%)

  • Culham (1m separation- 1.5%)

  • Wilkinson et al (2000)



How often do populations coincide?





Sympatry Likelihood Map



Total hybrid number per annum



Conclusions

  • The number and distribution of hybrids determine the scale, speed and possibility of any subsequent ecological change

  • Hybrid numbers in a country determines the feasibility of corrective measures

  • Error estimates will be fairly large initially but can be improved

  • Hybrid frequency estimates should be followed by measures of other parts of the pathway to change



Thoughts

  • Quantification of each stage in the pathway to change is possible but requires consideration of location, context and biology of both crop and recipient

  • Quantification requires effort to integrate data from different disciplines

  • Information generated is generic for the crop in the country concerned




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