Pollen flow in wheat revisited

Pollen Flow in Wheat Revisited: 

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

Why renewed interest in pollen flow in wheat?: 

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

How does gene flow via pollen drift occur?: 

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.

Facts about wheat pollen: 

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

Factors affecting gene flow via pollen: 

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

Gene Flow via pollen in Wheat – Current State of Knowledge: 

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

How far can wheat pollen move?: 

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

Pollination of a male sterile : 

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

Summary on pollen movement: 

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

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

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: 

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 : 

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

Slide13: 

Source: Ostby et al., 2004

Factors conferring varietal differences in cross-pollination propensity: 

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

What are the practical implications of these data?: 

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

What are typical isolation distances in “IP” systems in ND currently?: 

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

Results: 

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

Results: 

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

Results: 

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

Summary on isolation distances: 

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

Conclusions: 

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

Conclusions: 

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?