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Pollen Flow in Wheat Revisited

Pollen Flow in Wheat Revisited. Joel Ransom Extension Agronomist – Cereal Crops. Why renewed interest in pollen flow in wheat?. Steady progress in the development of wheat with transgenic traits Certain markets have indicated that they require non-transgenic wheat

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Pollen Flow in Wheat Revisited

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  1. Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

  2. Why renewed interest in pollen flow in wheat? • Steady progress in the development of wheat with transgenic traits • Certain markets have indicated that they require non-transgenic wheat • Pollen drift is one of many factors to consider when maintaining segregation • Information on out-crossing in wheat can help design effective identity preserved (IP) programs

  3. How does gene flow via pollen drift occur? • Some biology: • Pollen is produced in anthers • Fertilization requires viable pollen to attach to a receptive stigma and the successful transfer to genetic material to the ovule.

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

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

  6. Gene Flow via pollen in Wheat – Current State of Knowledge • Review of pollen movement studies • Review of information from out-crossing studies • Isolation distances • Varietal effects

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

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

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

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

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

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

  13. Source: Ostby et al., 2004

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

  15. What are the practical implications of these data? • Environment and variety can influence level of OC • In the two studies with spring wheat summarized a distance > 33-59 ft sufficient gave zero outcrossing in HRSW • Isolation distance >90: high probability of zero or minimal out-crossing

  16. What are typical isolation distances in “IP” systems in ND currently? • Methodology • Fields (within/between farms) sampled • 8 Organic fields • 8 certified/foundation seed production fields • 3 IP fields • Distance between closest wheat crop measured (all edges and corners) • Distance of natural isolation distance measured

  17. Results • Organic production fields (isolation required from non-organic fields - ? distance) • Natural isolation • Minimum distance – 0 ft • Maximum – 250 ft • Average – 57 ft • Median – 45 ft • Actual • Minimum distance - 48 • Maximum – 21,120 • Average - 2640 • Median - 2640

  18. Results • Certified Seed Production (current regulations – 5 ft) • Natural isolation • Minimum distance – 0 ft • Maximum – 165 ft • Average – 43 ft • Median – 42 ft • Actual • Minimum distance - 5 • Maximum – 21,120 • Average – 4,933 • Median – 2,640

  19. Results • Identity Preserved (isolation specified in contract) • Natural isolation • Minimum distance – 0 ft • Maximum – 500 ft • Average – 97 ft • Median – 50 ft • Actual • Minimum distance – 1 ft • Maximum – 15,840 ft • Average – 2,039 ft • Median – 152 ft

  20. Summary on isolation distances • Natural boundaries typically 50+ feet • “Fields” are not always separated by natural boundaries • If new standards of OC established for non-transgenic wheat requiring greater isolation (i.e. 60-90 ft): • Most but not all IP fields currently close to these distances • Seed production would be most impacted

  21. Conclusions • With an isolation distance of 60 - 90 ft (conservative based on the most promiscuous cultivar) there is limited risk of gene flow via pollen between cultivars of HRSW • Zero tolerance cannot be guaranteed with this distance, however, as pollen is capable of much farther movement • Current IP systems frequently have isolation distances approaching 60 ft, but sometimes much less • Natural boundaries alone for isolation is not workable due to layout of fields

  22. Conclusions • Revised isolation distances in IP would likely not be too difficult to achieve • Isolation distances in seed production would need to be revised to ensure increased purity • Given limited out-crossing and current field layouts, gene flow from transgenic wheat to non-transgenic wheat will likely be minimal and manageable. Other factors in segregation process will present greater challenges?

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