Gene Flow Through Pollen Drift: A Scientific Perspective

1. Gene Flow Through Pollen Drift: A Scientific Perspective Joel Ransom Extension Agronomist – Cereal Crops

2. Gene Flow • Movement of gametes (i.e. pollen), zygotes (seeds) and plants from one place to another and their incorporation into the gene pool at the new locality (Slatkin, 1987). • Occurs naturally via • Seed dispersal • Pollen movement

3. For the purpose of this presentation, focus is on the transfer of genes, mainly transgenes, from one crop variety to another. • Pollen drift does not equal gene flow (fertilization must occur) • Can include gene movement to related species (i.e. wheat and jointed goatgrass).

4. Renewed interest in pollen flow • Development of transgenic wheat • Adverse reception of trangenics in some markets • Segregation of trangenics from non-trangenics important • Pollen drift data can be used to develop policies and procedures for maintaining segregation (IP programs)

5. How does gene flow via pollen drift occur? • Some biology: • Pollen is produced in anthers • Pollen is released by anthers – “anthesis” • Fertilization requires viable pollen to attach to a receptive stigma and the successful transfer to DNA to the ovule.

6. Factors affecting gene flow • Crop • Corn – Cross pollinated (wind), isolations of 660’ • Canola - Cross pollinated (wind and insects), isolations of > 1,320’ • Barley – Self pollinated (flowers in the boot), isolations of 5’ • Soybean – Self pollinated, isolations of 5 ft’

7. Factors affecting gene flow • Distance between plants • Temperature • Humidity • Wind • Insects • Variety • Receptivity of the stigma • ‘Nick’ (synchrony of flowering) • Pollen viability

8. Gene Flow in Wheat – Current State of Knowledge • Review of pollen movement studies • Review of information from fertilization studies • Isolation distances • Varietal effects

9. Facts about wheat pollen • Relatively heavy • Viable for 2 to 20 minutes • 2,000 to 4,000 pollen grains per flower

10. How far can wheat pollen move? Adapted from Khan et al, 1973 (Kansas)

11. Pollination of a male sterile Adapted from Khan et al, 1973

12. Pollination of a male sterile Y=0 36 ft 41 ft 34 ft Adapted from J. Miller et al., 1975. 7 locations in ND

13. Summary on pollen movement • Viable wheat pollen can move > 150 ft • Zero tolerance will be unworkable • Based on male sterile plants, cross pollination risk greatest in first 20 ft of isolation from source • Fertilization success dependant on pollen concentration

14. Summary of studies quantifying cross fertilization in traditional wheat

15. Effect of variety and year on out-crossing in Kansas, HRWW Adapted from Martin, 1990

16. Effect of variety and year on out-crossing (92-93), HRSW, Canada Adapted from Hucl, 1996

17. Effect of isolation distance on out-crossing of four Canadian wheat cultivars, 1995 Adapted from Hucl & Matus-Cadiz, 2001

18. Out-crossed seed number by distance Oslo Katepwa Distance (ft) Percent Seed/bu Percent Seed/bu

19. Factors conferring varietal differences in cross-pollination propensity • Glume opening • Extrusion of anthers • Duration of opening • Open spikelets vs dense spikes

20. What are the practical implications of these data? • Gene flow between transgenic and non-transgenic varieties will depend on • Distance from pollen source • Variety • Environment • Isolation distance for < 0.01% • most varieties = 10 ft • Promiscuous varieties = 80 ft

21. Management Recommendations for non-GMO IP programs • Maintain isolations of 90 ft (conservative based on the most promiscuous cultivar) • Use border rows to “flood” field with non-GMO pollen • Use different planting dates and maturity types than GMO neighbors • Use pure seed and clean equipment

22. Conclusions • Wheat pollen can move significant distances (>200 ft) • Tolerance levels of transgenes are needed; zero tolerance will not be workable • Gene flow is dependant on environment, varieties grown and isolation distance • Data on out-crossing potential of ND varieties is needed for refining segregation strategies

23. Conclusions • Gene flow through pollen drift is low in wheat and IP programs for non-GMO cultivars should not be difficult • Use isolation distances > 90 ft and follow other practices that reduce the risk of cross pollination • Avoiding physical mixtures will be key • Seedstocks and soybeans • 2 of 4 soybean fields in Iowa GMO in seed