The Dynamics of Multiple Infection
in Pyrenophora semeniperda
Trevor Davis and Julie Beckstead, Gonzaga University,
Department of Biology
Cheatgrass Invasion
• Native to Eurasia
• Transported in crop
seed
• Found in all U.S. states
• Outcompetes natives
• Alters fire cycle
• Persistent seedbank
Pyrenophora semeniperda
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Fungus: “BFOD”
Possible biocontrol
Naturally occurring
Seed Pathogen
Generalist
High infection and
death rates in
cheatgrass
Multiple Infections
• Species and strains
• Common in nature
• Complicated:
competition, toxins,
genetics, growth rate,
virulence.
• Varied response
• May affect BFOD
Research Questions
• Will co-infecting species and strains of
fungi reduce BFOD’s potential as a
biocontrol?
• What characteristics of two co-infectors’
relationship determines their response to
one another?
Materials and Methods
• Double inoculation
• Species and
strains
• Blotter-plate
bioassays
• Analyze seeds and
stromata
Treatment
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Proportion Seeds Infected
Experiment 1: Species
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Research Question
• Will co-infecting species of fungi reduce
BFOD’s potential as a biocontrol?
Probably not.
Experiment 2: Strains
1
0.9
Proportion Seeds Infected
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
WRK6
WRK6+MIL17
WRK6+MLV2
Treatment
WRK6+TMC16
WRK6+WHV2
Research Question
• Will co-infecting strains of fungi reduce
BFOD’s potential as a biocontrol?
No.
Experiment 2 contd.
Proportion Seeds Infected
1
0.9
Virulent
Fast
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
MLV7
TMC23
Inoculum
MLV7+TMC23
Research Question
• What characteristics of two co-infectors’
relationship determines their response to
one another?
Virulence > Growth Rate
Conclusions
• Co-infectors will not affect BFOD’s
performance as a biocontrol.
• Minimal (<30% impact)
• Reduction in virulence offset by high
inoculum load
• Inoculation combined with other
methods
Conclusions contd.
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Co-infections may be useful
Combine strains for application
Example: virulent kills, fast-growing “eats”
Lessens risk of non-target death
Location-specific genotypes
Acknowledgements
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Dr. Julie Beckstead
Dr. Susan Meyer
Dr. David Boose
Dr. Ann Kennedy
Sandra Dooley
Laura Street
Kellene Bergen
Lindsay Poston
Lauren Miller
Kristina Bair
Stephen Harrison