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

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). 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 Occurs naturally via –Seed dispersal –Pollen movement

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

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

How does gene flow via pollen drift occur? Some biology: 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.

Factors affecting gene flow Crop 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’

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

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

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

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

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

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

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

Summary of studies quantifying cross fertilization in traditional wheat STUDYRESULTSCOMMENTS 1932, Harrington (Saskatoon) 0.0 – 2.16% (Mean 0.79%) 5 females and 6 pollinators over 5 yrs. at 1 ft. 1980, Allen (Oregon) 3 – 4% Adjacent rows 1984, Martin (Kansas) 0.3 – 3.1% (Mean 1.2%) Avg. over 3 years at 1 ft. on 11 HRWW cultivars 1987, Griffin (New Zealand) 0.14 – 3.95% (Mean 1.1%) 10 spring cultivars at 1 ft. with no significant differences 1993, Hucl (Saskatoon) 0.22 – 4.64% (Mean 0.89%) Avg. over 2 yrs. at 8 inches with 11 cultivars 2001, Hucl (Saskatoon) 0.2 – 3.8% (Mean 0.77%) 4 spring cultivars over 2 yrs. at 1 ft.

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

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

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

Out-crossed seed number by distance , , , OsloKatepwa Percent Seed/bu Distance (ft)

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

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

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

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

Conclusions Gene flow through pollen drift is low in wheat and IP programs for non-GMO cultivars should not be difficult 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 Seedstocks and soybeans 2 of 4 soybean fields in Iowa GMO in seed 2 of 4 soybean fields in Iowa GMO in seed