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

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

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

Pollen Flow in Pollen Flow in Wheat Wheat RevisitedRevisited

Joel RansomExtension Agronomist – Cereal Crops

Page 2: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Why renewed interest in Why renewed interest in pollen flow in wheat?pollen flow in wheat?

Steady progress in the development Steady progress in the development of wheat with transgenic traitsof wheat with transgenic traits

Certain markets have indicated that Certain markets have indicated that they require non-transgenic wheat they require non-transgenic wheat

Pollen drift is one of many factors to Pollen drift is one of many factors to consider when maintaining consider when maintaining segregation segregation

Information on out-crossing in Information on out-crossing in wheat can help design effective wheat can help design effective identity preserved (IP) programsidentity preserved (IP) programs

Page 3: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

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

– Pollen is produced in Pollen is produced in anthersanthers

– Fertilization requires Fertilization requires viable pollen to attach viable pollen to attach to a receptive stigma to a receptive stigma and the successful and the successful transfer to genetic transfer to genetic material to the ovule.material to the ovule.

Page 4: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Facts about wheat Facts about wheat pollenpollen Relatively heavyRelatively heavy Viable for 2 to 20 Viable for 2 to 20

minutesminutes 2,000 to 4,000 pollen 2,000 to 4,000 pollen

grains per flowergrains per flower

Page 5: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Factors affecting gene flow Factors affecting gene flow via pollenvia pollen Distance between Distance between

plantsplants TemperatureTemperature HumidityHumidity WindWind InsectsInsects VarietyVariety Receptivity of the Receptivity of the

stigmastigma ‘‘Nick’ (synchrony ofNick’ (synchrony of

flowering) flowering) Pollen viabilityPollen viability

Page 6: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Gene Flow via pollen in Gene Flow via pollen in Wheat – Current State of Wheat – Current State of KnowledgeKnowledge

Review of pollen Review of pollen movement studiesmovement studies

Review of Review of information from information from out-crossing out-crossing studiesstudies– Isolation distancesIsolation distances– Varietal effectsVarietal effects

Page 7: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

How far can wheat pollen How far can wheat pollen move?move?

0

20

40

60

80

100

0 20 39 59 79 98 118 138 157

Distance from pollen source in ft

Pollen g

rain

s/17m

m2

1968 1969

Adapted from Khan et al, 1973 (Kansas)

Page 8: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Pollination of a male Pollination of a male sterilesterile

0

10

20

30

40

50

0 20 39 59 79 98 118 138 157

Distance from pollen source in ft

% s

eed s

et

1966 1968 1969

Adapted from Khan et al, 1973

Page 9: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Summary on pollen Summary on pollen movementmovement Viable wheat pollen can Viable wheat pollen can

move > 150 ftmove > 150 ft Based on male sterile Based on male sterile

plants, cross pollination plants, cross pollination risk greatest in first 20 ft risk greatest in first 20 ft of isolation from sourceof isolation from source– Fertilization success Fertilization success

dependant on pollen dependant on pollen concentrationconcentration

Page 10: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

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

0123456

KS7521

0

Newto

n

TAM 1

05

Larned

Eagle

Arkan

Trium

ph 6

4

Bennet

t

Bucksk

in

Win

gsVona

Centu

rk

% o

utc

ross

ing

1982 1983 1984

Adapted from Martin, 1990

Page 11: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Effect of variety and year on Effect of variety and year on out-crossing (92-93), HRSW, out-crossing (92-93), HRSW, CanadaCanada

0123456

Bigga

r

Gen

esis

Osl

o

Rongote

a

Wild

cat

Gle

nlea

Katep

wa

Laura

CDC Mak

wa

Colum

bus

Roblin

% o

utc

ross

ing

1992 1993

Adapted from Hucl, 1996

Page 12: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

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

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60 70 80

Distance from pollen source in ft

% o

ut-

cross

ing Katepwa Biggar Roblin Oslo

Adapted from Hucl & Matus-Cadiz, 2001

Page 13: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Effect of spatial separation on OC in 4 varieties, Prosper, ND, 2004.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1.1 13 33 110

Separation distance (ft)

% O

utc

ross

ing

Alsen Granite Explorer Oslo

Source: Ostby et al., 2004

Page 14: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Factors conferring varietal Factors conferring varietal differences in cross-differences in cross-pollination propensitypollination propensity Glume openingGlume opening Extrusion of Extrusion of

anthersanthers Duration of Duration of

openingopening Open spikelets vs Open spikelets vs

dense spikesdense spikes

Page 15: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

What are the practical What are the practical implications of these implications of these data?data?

Environment and variety Environment and variety can influence level of OC can influence level of OC

In the two studies with In the two studies with spring wheat spring wheat summarized a distance summarized a distance > 33-59 ft sufficient > 33-59 ft sufficient gave zero outcrossing in gave zero outcrossing in HRSWHRSW

Isolation distance >90: Isolation distance >90: high probability of zero high probability of zero or minimal out-crossingor minimal out-crossing

Page 16: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

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

– Fields (within/between farms) sampledFields (within/between farms) sampled 8 Organic fields8 Organic fields 8 certified/foundation seed production 8 certified/foundation seed production

fieldsfields 3 IP fields3 IP fields

– Distance between closest wheat crop Distance between closest wheat crop measured (all edges and corners)measured (all edges and corners)

– Distance of natural isolation distance Distance of natural isolation distance measuredmeasured

Page 17: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

ResultsResults

Organic production fields Organic production fields (isolation required from non-(isolation required from non-organic fields - ? distance)organic fields - ? distance)– Natural isolationNatural isolation

Minimum distance – 0 ftMinimum distance – 0 ft Maximum – 250 ft Maximum – 250 ft Average – 57 ftAverage – 57 ft Median – 45 ftMedian – 45 ft

– ActualActual Minimum distance - 48Minimum distance - 48 Maximum – 21,120Maximum – 21,120 Average - 2640Average - 2640 Median - 2640Median - 2640

Page 18: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

ResultsResults

Certified Seed Certified Seed Production (current Production (current regulations – 5 ft)regulations – 5 ft)– Natural isolationNatural isolation

Minimum distance – 0 ftMinimum distance – 0 ft Maximum – 165 ft Maximum – 165 ft Average – 43 ftAverage – 43 ft Median – 42 ftMedian – 42 ft

– ActualActual Minimum distance - 5Minimum distance - 5 Maximum – 21,120Maximum – 21,120 Average – 4,933Average – 4,933 Median – 2,640Median – 2,640

Page 19: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

ResultsResults

Identity Preserved Identity Preserved (isolation specified in (isolation specified in contract)contract)– Natural isolationNatural isolation

Minimum distance – 0 ftMinimum distance – 0 ft Maximum – 500 ft Maximum – 500 ft Average – 97 ftAverage – 97 ft Median – 50 ftMedian – 50 ft

– ActualActual Minimum distance – 1 ftMinimum distance – 1 ft Maximum – 15,840 ftMaximum – 15,840 ft Average – 2,039 ftAverage – 2,039 ft Median – 152 ftMedian – 152 ft

Page 20: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

Summary on isolation Summary on isolation distancesdistances

Natural boundaries typically 50+ feetNatural boundaries typically 50+ feet ““Fields” are not always separated by Fields” are not always separated by

natural boundaries natural boundaries If new standards of OC established If new standards of OC established

for non-transgenic wheat requiring for non-transgenic wheat requiring greater isolation (i.e. 60-90 ft):greater isolation (i.e. 60-90 ft):– Most but not all IP fields currently close Most but not all IP fields currently close

to these distancesto these distances– Seed production would be most Seed production would be most

impactedimpacted

Page 21: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

ConclusionsConclusions

With an isolation distance of 60 - 90 ft With an isolation distance of 60 - 90 ft (conservative based on the most (conservative based on the most promiscuous cultivar) there is limited promiscuous cultivar) there is limited risk of gene flow via pollen between risk of gene flow via pollen between cultivars of HRSWcultivars of HRSW

Zero tolerance cannot be guaranteed Zero tolerance cannot be guaranteed with this distance, however, as pollen is with this distance, however, as pollen is capable of much farther movementcapable of much farther movement

Current IP systems frequently have Current IP systems frequently have isolation distances approaching 60 ft, isolation distances approaching 60 ft, but sometimes much lessbut sometimes much less

Natural boundaries alone for isolation is Natural boundaries alone for isolation is not workable due to layout of fieldsnot workable due to layout of fields

Page 22: Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops

ConclusionsConclusions

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

Isolation distances in seed production Isolation distances in seed production would need to be revised to ensure would need to be revised to ensure increased purity increased purity

Given limited out-crossing and current Given limited out-crossing and current field layouts, gene flow from field layouts, gene flow from transgenic wheat to non-transgenic transgenic wheat to non-transgenic wheat will likely be minimal and wheat will likely be minimal and manageable. Other factors in manageable. Other factors in segregation process will present segregation process will present greater challenges?greater challenges?