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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 l.jpg

Pollen Flow in Wheat Revisited

Joel Ransom

Extension Agronomist – Cereal Crops


Why renewed interest in pollen flow in wheat l.jpg
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


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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.


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Facts about wheat pollen

  • Relatively heavy

  • Viable for 2 to 20 minutes

  • 2,000 to 4,000 pollen grains per flower


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Factors affecting gene flow via pollen

  • Distance between plants

  • Temperature

  • Humidity

  • Wind

  • Insects

  • Variety

  • Receptivity of the stigma

  • ‘Nick’ (synchrony of flowering)

  • Pollen viability


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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


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How far can wheat pollen move?

Adapted from Khan et al, 1973 (Kansas)


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Pollination of a male sterile

Adapted from Khan et al, 1973


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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


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Effect of variety and year on out-crossing in adjacent plants in Kansas, HRWW

Adapted from Martin, 1990



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Effect of isolation distance on out-crossing of four Canadian wheat cultivars, 1995

Adapted from Hucl & Matus-Cadiz, 2001


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Source: Ostby et al., 2004 Canadian wheat cultivars, 1995


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Factors conferring varietal differences in cross-pollination propensity

  • Glume opening

  • Extrusion of anthers

  • Duration of opening

  • Open spikelets vs dense spikes


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What are the practical implications of these data? propensity

  • 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


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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


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Results ND currently?

  • 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


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Results ND currently?

  • 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


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Results ND currently?

  • 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


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Summary on isolation distances ND currently?

  • 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


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Conclusions ND currently?

  • 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


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Conclusions ND currently?

  • 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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