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

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

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

Factors affecting gene flow via pollen 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 via pollen in Wheat – Current State of Knowledge Review of pollen movement studies Review of pollen movement studies Review of information from out-crossing studies Review of information from out-crossing studies –Isolation distances –Varietal effects

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

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

Summary on pollen movement Viable wheat pollen can move > 150 ft Viable wheat pollen can move > 150 ft 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

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

Source: Ostby et al., 2004

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? Environment and variety can influence level of OC Environment and variety can influence level of OC In the two studies with spring wheat summarized a distance > ft sufficient gave zero outcrossing in HRSW In the two studies with spring wheat summarized a distance > ft sufficient gave zero outcrossing in HRSW Isolation distance >90: high probability of zero or minimal out-crossing Isolation distance >90: high probability of zero or minimal out-crossing

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

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

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

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

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

Conclusions With an isolation distance of ft (conservative based on the most promiscuous cultivar) there is limited risk of gene flow via pollen between cultivars of HRSW With an isolation distance of 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 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 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 Natural boundaries alone for isolation is not workable due to layout of fields

Conclusions Revised isolation distances in IP would likely not be too difficult to achieve 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 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? 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?