Gene Flow Gene Flow Through Through Pollen Drift: Pollen Drift: A Scientific A Scientific PerspectivePerspective

Joel RansomExtension Agronomist – Cereal Crops

Gene FlowGene Flow

Movement of gametes (i.e. pollen), Movement of gametes (i.e. pollen), zygotes (seeds) and plants from one zygotes (seeds) and plants from one place to another and their place to another and their incorporation into the gene pool at the incorporation into the gene pool at the new locality (Slatkin, 1987). new locality (Slatkin, 1987).

Occurs naturally viaOccurs naturally via– Seed dispersalSeed dispersal– Pollen movementPollen movement

For the purpose of this For the purpose of this presentation, focus is on presentation, focus is on the transfer of genes, the transfer of genes, mainly transgenes, from mainly transgenes, from one crop variety to another.one crop variety to another.

Pollen drift does not equal Pollen drift does not equal gene flow (fertilization must gene flow (fertilization must occur)occur)

Can include gene Can include gene movement to related movement to related species (i.e. wheat and species (i.e. wheat and jointed goatgrass).jointed goatgrass).

Renewed interest in pollen Renewed interest in pollen flowflow Development of transgenic wheatDevelopment of transgenic wheat Adverse reception of trangenics in Adverse reception of trangenics in

some marketssome markets Segregation of trangenics from non-Segregation of trangenics from non-

trangenics important trangenics important Pollen drift data can be used to Pollen drift data can be used to

develop policies and procedures for develop policies and procedures for maintaining segregation (IP programs)maintaining segregation (IP programs)

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

– Pollen is released by Pollen is released by anthers – “anthesis”anthers – “anthesis”

– 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 DNA to the transfer to DNA to the ovule.ovule.

Factors affecting gene flowFactors affecting gene flow

CropCrop– CornCorn – Cross pollinated – Cross pollinated

(wind), isolations of 660’(wind), isolations of 660’– CanolaCanola - Cross pollinated - Cross pollinated

(wind and insects), (wind and insects), isolations of > 1,320’isolations of > 1,320’

– BarleyBarley – Self pollinated – Self pollinated (flowers in the boot), (flowers in the boot), isolations of 5’isolations of 5’

– SoybeanSoybean – Self pollinated, – Self pollinated, isolations of 5 ft’isolations of 5 ft’

Factors affecting gene flowFactors affecting gene flow

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

Gene Flow in Wheat – Gene Flow in Wheat – Current State of KnowledgeCurrent State of Knowledge

Review of pollen Review of pollen movement studiesmovement studies

Review of Review of information from information from fertilization fertilization studiesstudies– Isolation distancesIsolation distances– Varietal effectsVarietal effects

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

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)

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

Pollination of a male Pollination of a male sterilesterile

0

10

20

30

40

50

60

70

4.3 8.34 12.7 17

Distance from pollen source in ft

% s

eed s

et

1972 1973 1973

Adapted from J. Miller et al., 1975. 7 locations in ND

Y=0

36 ft

41 ft

34 ft

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

move > 150 ftmove > 150 ft– Zero tolerance will be Zero tolerance will be

unworkableunworkable 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

Summary of studies quantifying cross Summary of studies quantifying cross fertilization in traditional wheatfertilization in traditional wheat

STUDYSTUDY RESULTSRESULTS COMMENTSCOMMENTS

1932, Harrington 1932, Harrington (Saskatoon)(Saskatoon)

0.0 – 2.16% 0.0 – 2.16% (Mean 0.79%)(Mean 0.79%)

5 females and 6 pollinators over 5 yrs. 5 females and 6 pollinators over 5 yrs. at 1 ft.at 1 ft.

1980, Allen 1980, Allen (Oregon)(Oregon)

3 – 4%3 – 4% Adjacent rowsAdjacent rows

1984, Martin 1984, Martin (Kansas)(Kansas)

0.3 – 3.1% 0.3 – 3.1% (Mean 1.2%)(Mean 1.2%)

Avg. over 3 years at 1 ft. on 11 Avg. over 3 years at 1 ft. on 11 HRWW cultivarsHRWW cultivars

1987, Griffin 1987, Griffin (New Zealand)(New Zealand)

0.14 – 3.95% 0.14 – 3.95% (Mean 1.1%)(Mean 1.1%)

10 spring cultivars at 1 ft. with no 10 spring cultivars at 1 ft. with no significant differencessignificant differences

1993, Hucl 1993, Hucl (Saskatoon)(Saskatoon)

0.22 – 4.64% 0.22 – 4.64% (Mean 0.89%)(Mean 0.89%)

Avg. over 2 yrs. at 8 inches with 11 Avg. over 2 yrs. at 8 inches with 11 cultivarscultivars

2001, Hucl 2001, Hucl (Saskatoon)(Saskatoon)

0.2 – 3.8% 0.2 – 3.8% (Mean 0.77%)(Mean 0.77%)

4 spring cultivars over 2 yrs. at 1 ft.4 spring cultivars over 2 yrs. at 1 ft.

Effect of variety and year on Effect of variety and year on out-crossing in Kansas, out-crossing in Kansas, HRWWHRWW

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

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

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

Out-crossed seed number by Out-crossed seed number by distancedistance

0-100-10 1.271.27 11,53011,530 0.010.01 9090

10-2010-20 0.450.45 4,0904,090 0.000.00 00

20-4020-40 0.180.18 1,6301,630 0.000.00 00

8080 0.000.00 00 0.000.00 00

Oslo Katepwa

Percent Percent Seed/buSeed/buDistance (ft)

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

What are the practical What are the practical implications of these implications of these data?data? Gene flow between Gene flow between

transgenic and non-transgenic and non-transgenic varieties will transgenic varieties will depend ondepend on– Distance from pollen sourceDistance from pollen source– VarietyVariety– EnvironmentEnvironment

Isolation distance for < Isolation distance for < 0.01%0.01%– most varieties = 10 ftmost varieties = 10 ft– Promiscuous varieties = 80 Promiscuous varieties = 80

ftft

Management Recommendations Management Recommendations for non-GMO IP programsfor non-GMO IP programs

Maintain isolations of 90 ft Maintain isolations of 90 ft (conservative based on the most (conservative based on the most promiscuous cultivar)promiscuous cultivar)

Use border rows to “flood” field Use border rows to “flood” field with non-GMO pollenwith non-GMO pollen

Use different planting dates and Use different planting dates and maturity types than GMO neighborsmaturity types than GMO neighbors

Use pure seed and clean equipmentUse pure seed and clean equipment

ConclusionsConclusions

Wheat pollen can move significant Wheat pollen can move significant distances (>200 ft)distances (>200 ft)

Tolerance levels of transgenes are Tolerance levels of transgenes are needed; zero tolerance will not be needed; zero tolerance will not be workableworkable

Gene flow is dependant on Gene flow is dependant on environment, varieties grown and environment, varieties grown and isolation distanceisolation distance

Data on out-crossing potential of ND Data on out-crossing potential of ND varieties is needed for refining varieties is needed for refining segregation strategiessegregation strategies

ConclusionsConclusions

Gene flow through pollen drift is low Gene flow through pollen drift is low in wheat and IP programs for non-in wheat and IP programs for non-GMO cultivars should not be difficultGMO cultivars should not be difficult– Use isolation distances > 90 ft and Use isolation distances > 90 ft and

follow other practices that reduce the follow other practices that reduce the risk of cross pollinationrisk of cross pollination

– Avoiding physical mixtures will be keyAvoiding physical mixtures will be key Seedstocks and soybeansSeedstocks and soybeans 2 of 4 soybean fields in Iowa GMO in seed2 of 4 soybean fields in Iowa GMO in seed