Pollen Flow in Wheat Revisited Joel Ransom Extension Agronomist – Cereal Crops.
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Transcript of 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
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
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.
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
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
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
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
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
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
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
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
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?
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
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
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
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
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
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
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
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?