Integrating the biological and physical components of maize pollen dispersal Mark Westgate, Ray Arritt, and Susana Goggi Iowa State University
Integrating the biological and physical components of maize
pollen dispersal
Mark Westgate, Ray Arritt, and Susana GoggiIowa State University
Biological and Physical Components of Out-crossing
• Biological (source)– Pollen shed characteristics
• Timing, intensity, viability
• Physical (delivery system)– Topography
• Distance, elevation, wind breaks, border rows– Atmospheric conditions
• Wind speed, wind direction, stability index, mixing height, air temperature, relative humidity
• Biological (receiver field)– Pollen shed characteristics– Synchrony with female and adventitious pollen source – Specific combining ability
Structure of pollen production, Structure of pollen production, dispersal, and outdispersal, and out--crossing modelcrossing model
MeteorologicalAnalysis or
Model
Pollen Pollen TransportTransport Pollen ViabilityPollen Viability
WeatherData
TopographicDataCrop Data
Pollen Shed
ReceptorRisk
Pollen production Pollen production
MeteorologicalAnalysis or
Model
Pollen Transport Pollen Viability
WeatherData
TopographicDataCrop Data
Pollen Shed
ReceptorRisk
Hybrid A
0.0E+00
3.0E+05
6.0E+05
9.0E+05
1.2E+06
1.5E+06
1.8E+06
24-Jul 26-Jul 28-Jul 30-Jul 1-Aug 3-Aug 5-Aug
Polle
n gr
ains
she
d pe
r tas
sel
1 pl/m28 pl/m218 pl/m2Poly. (1 pl/m2)Poly. (8 pl/m2)Poly. (18 pl/m2)
Pollen shed intensity typically peaks Pollen shed intensity typically peaks 2 days after first anthers appear 2 days after first anthers appear
192 196 200 204 208Pol
len
shed
rate
(gra
ins
cm-2
d-1
)
Actual Predicted
Day of the year194 198 202 206 210
0
200
400
600
800
Per
cent
of p
opul
atio
n (%
)
0
20
40
60
80
100BeginMax End
P3978 P3925
100% MF 75% MF
PI
• Pollen shed characteristics• Timing, intensity, viability
Timing of pollen shed can be Timing of pollen shed can be simulated from tassel development simulated from tassel development
and population dynamicsand population dynamics
Diurnal patterns of pollen shed vary
7/29
020406080
100120140160180
6:00 8:00 10:00 12:00 14:00 16:00
Time of day
Polle
n gr
ains
/cm
2Temp, RH, and wind speed affect the initiation and
intensity of pollen shedShed typically begins at RH < 90%
Pollen dispersal Pollen dispersal
MeteorologicalAnalysis or
Model
Pollen Pollen TransportTransport Pollen ViabilityPollen Viability
WeatherData
TopographicDataCrop Data
Pollen Shed
ReceptorRisk
• Physical (delivery system)– Topography
• Distance, elevation, wind breaks, border rows– Atmospheric conditions
• Wind speed, wind direction, stability index, mixing height, air temperature, relative humidity
Adapted from Di-Giovanni and Kevan, 1991
Gaussian plume
Statistical
Diffusion
Adapted from Di-Giovanni and Kevan, 1991Adapted from Di-Giovanni and Kevan, 1991
Gaussian plume
Statistical
Diffusion
Pollen transport models• Lagrangian random-walk approach
– the pollen cloud is represented as a population of virtual “particles”
– each virtual particle can be traced according to its source, path, or other property of interest
• Gaussian plume approach– the pollen cloud is ‘constrained’ to a normal
distribution that is modified hourly by local atmospheric conditions
Physical parameters for modeling maize pollen dispersal are fairly well established
---- weight/grain: weight/grain: 250 to 350 250 to 350 ngng---- diameter: diameter: 50 to 90 50 to 90 µµMM---- density: density: 1.25 to 1.45 g cm1.25 to 1.45 g cm--33
---- settling velocity: settling velocity: 20 20 –– 32 cm s32 cm s--11
---- number per plant: number per plant: 0.5 to 6 x 100.5 to 6 x 1066
---- duration of shed: duration of shed: 4 to 6 days4 to 6 days
Field evaluation of the pollen transport models:
• 9 monitoring locations within the source field
• Receptors (sticky traps) placed at 5, 10, 30, 90, 165, 330, and 660 feet from the edge of the source field in the 8 major directional axes
• Pollen dispersal monitored from 0730 to 1700 hours.
Daily and seasonal patterns of pollen dispersal from a source field can be simulated fairly accurately
July 21, 2000
g/m2
1 pollen grain/4 cm2
at 0.25 pollen grain/cm2dpotential contamination ~ 0.28%
or ~ 3 kernels per 1000 exposed silks
100m
July 21, 2000
g/m2
1 pollen grain/4 cm2
at 0.25 pollen grain/cm2dpotential contamination ~ 0.28%
or ~ 3 kernels per 1000 exposed silks
100m100m100m
Lagrangian numerical simulation-- Arritt et al. ISU
Gaussian plume– ISCST3/AERMOD EPA models
…but both models tend to overestimate deposition near the source field, and underestimate deposition at greater distances
from Riese, 2004
Lagrangian model
Values summed for eight cardinal directions from source fieldPo
llen
depo
sitio
n (g
rain
s/cm
2da
y)
ISCST3
Need to account for modification of the 3D flow field by the crop (windbreak)and atmospheric turbulence on a larger scale (large eddy simulation).
Pollen viability decreases linearly with moisture content.
Pollen of the ‘average’ maize genotype loses viability completely at about 30% moisture
Average values for 11 genotypes
Initial viability 80%PMC at 0% 30%
Pollen/tassel 3.1E6
Loss of pollen moisture is an exponential function of VPD and time
tVPDePMC 0012.02.63 −=
0
200
400
600
800
1000
1200
0 20 40 60 80
Viability (percent)
Peak
Par
ticle
Hei
ght (
m)
Topeka PM Omaha PM
“Terminal viability” of lofted maize pollen
• Pollen lofted through two representative atmospheric soundings (updraft at 3 m/s, fall at 20 cm/s)
• Viability adjusted accounting for VPD through the profile until the pollen grain returned to the ground.
Brunet et al., 2004
Y-axis normalized to daily convective boundary layer, 800-2000m
OutOut--crossing crossing
MeteorologicalAnalysis or
Model
Pollen Transport Pollen Viability
WeatherData
TopographicDataCrop Data
Pollen Shed
ReceptorRisk
• Biological (receiver field)– Pollen shed characteristics– Synchrony with female and adventitious pollen source – Specific combining ability
““Nick ManagerNick Manager” converts daily estimates of pollen shed and silk emergence to ” converts daily estimates of pollen shed and silk emergence to simulate kernel set for any given field condition simulate kernel set for any given field condition
Temporal profile of silk exsertion (blue), temporal profile of pollen shed (black), and simulated daily values of kernel set (red).
Lizaso et al. 2003
Simulated kernel set in 13 seed production fieldsSimulated kernel set in 13 seed production fields
Fonseca et al. (unpublished)
Loss of pollen viability and pollen trapping by leaves not taken into account
0
10
20
30
40
50
60
Perc
ent o
f tot
al
obse
rvat
ions
0 2 4 6 8 10Percent outcross
199819992000
3-year seed industry study
Ireland et al 2004
A few mid-field samples had > 10% out-crosses
About 50% of the mid-field samples were free of out-crosses
Risk of OutRisk of Out--crossingcrossing
Field BRisk Index: 5.68Field BRisk Index: 5.68
Field CRisk Index: 4.65Field CRisk Index: 4.65
Early and late appearing silks at risk
Late appearing silks at risk
An example of simulated out-crossingresulting from “adventitous presence” late in flowering
Nick Manager Summary
0
5
10
15
20
25
30
195 200 205 210 215 220 225 230
Day of the year
Silk
s, K
erne
ls (h
a x
106 )
0
100
200
300
400
500
Pollen grains cm-2
Silks
Kernels
Silks at Risk
Local pollen
Adventitious pollen
Adventitious pollen peaked at 7.5 gr/cm2 on 216
Total kernel production21.8 mil kernels/ha
76.5% silks were pollinated98.4% genetically pure seed
1.6% out-crossed seed
Contamination by Pollen Movement
Seed FieldWest
Source
Durant, IA :1998Durant, IA :1998
2.0 2.0 2.0 2.0 0.0 0.0 0.250.25Percent OutPercent Out--crossingcrossing
12 14 12 14 16 16 18 18 20 20 22 2422 24JulyJuly
East PollenEast Pollen
West PollenWest Pollen
Seed field silkingSeed field silkingSeed fieldSeed field pollenpollen
WindRoseWindRose for Durant, IAfor Durant, IA1515--21 July 1998: 0800 21 July 1998: 0800 –– 1400 h1400 h
EastSource
100m
6:1:4:1
71a
100m
160a
80a
InterInter--industry Isolation Standards Studyindustry Isolation Standards Study
Seed FieldWest
Source
Durant, IA :1998Durant, IA :1998
2.0 2.0 2.0 2.0 0.0 0.0 0.250.25Percent OutPercent Out--crossingcrossing
12 14 12 14 16 16 18 18 20 20 22 2422 24JulyJuly
East PollenEast Pollen
West PollenWest Pollen
Seed field silkingSeed field silkingSeed fieldSeed field pollenpollen
12 14 12 14 16 16 18 18 20 20 22 2422 24JulyJuly
East PollenEast Pollen
West PollenWest Pollen
Seed field silkingSeed field silkingSeed fieldSeed field pollenpollen
WindRoseWindRose for Durant, IAfor Durant, IA1515--21 July 1998: 0800 21 July 1998: 0800 –– 1400 h1400 h
EastSource
100m
6:1:4:1
71a
100m
160a
80a
InterInter--industry Isolation Standards Studyindustry Isolation Standards Study