Crop Resistance to Insect Pests - University of Manitoba › faculties › afs › entomology ›...
Transcript of Crop Resistance to Insect Pests - University of Manitoba › faculties › afs › entomology ›...
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Crop Resistance to Insect Pests
Robert J. Lamb
Cereal Research CentreWinnipeg, MB, R3T 2M9
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What is crop resistance?
• The use of heritable plant traits to reduce plant damage resulting from insect herbivory
• Crop resistance is a relative phenomenon, eg. a plant genotype is more less resistant to insect herbivory than another plant genotype
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Types of resistance
• Antibiosis: growth and development of the pest are affected
• Non-preference (antixenosis): density of the pest infesting the plant is reduced
• Tolerance: plant supports the pest without loss of vigor or yield
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Lecture plan
• Domestication of crops, effects on resistance to herbivory
• Developing resistant crops: 2 examples
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Do crops become more susceptible to insect pests as they evolve as a result of selection by humans?
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Evolutionary relationships among wheats
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Glume
Larvae feed on a developing seed within the floret. The floret consists of 4 glumes that completely enclose and protect the seed.
Wheat midge
Seed
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Structure of a modern wheat spike
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Lineages of species in the genus Triticum -level indicates major evolutionary step
1. free threshing; 2. not free threshing; 3. glumes affixed to seed.
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Lineages of species in the genus Triticum -Level indicates major evolutionary step
Level
1123334
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Conclusion for wheat midge and wheat
• Humans selected free threshing wheat
• Free threshing wheat is more suitable for wheat midge
• Domestication has increased susceptibity of the crop
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Crop resistance to insect pests –
Hessian fly and wheat
wheat midge and wheat
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Hessian fly, Mayetiola destructor (Say)
Wheat leaf removed to expose puparium
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Wheat stem infested and broken by Hessian fly
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Wheat infested by Hessian fly
Severe Resistant Moderate
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Hessian fly infestation of row plots, 2000
Infested stems, %
02468
1012141618
Superb AC Barrie
Broken stems, %
02468
1012141618
Superb AC Barrie
±0.9
±3.9
±5.0
±3.9
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Hessian fly on seedlings in laboratory
Eggs per plant
0
2
4
6
8
Guard Superb Barrie
Larval survival, %
0
10
20
30
40
50
60
Guard Superb Barrie
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Resistance in seedlings in laboratory
• No deterrence of oviposition
• Antibiosis, expressed as reduced survival from egg to puparia
• Superb is antibiotic, but not as antibiotic as resistant standard Guard
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Stems infested (%) by Hessian fly - field
0
10
20
30
40
50
60
70
80
2000 2002 2003 2002-multi
SuperbBarrie
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Hessian fly infested stems that break, %
0
20
40
60
80
100
2000 2002 2003 2002-multi
SuperbBarrie
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Seed production on unbroken, infested stems
1000 seed wt, g
0
5
10
15
20
25
30
35
Superb Barrie
Un-InfInf
Seeds per spike
252627282930313233
Superb Barrie
Un-InfInf
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Resistance of Superb in the field
• Antibiosis that reduces infestation
• Tolerance that reduces the proportion of infested stems that break
• Tolerance that maintains the number of seeds on standing, infested stems
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Yield loss (%) from Hessian fly - field
0
20
40
60
80
2000 2002 2003
GuardSuperbBarrie
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Conclusions: • Superb shows substantial resistance to Hessian fly
• Resistance results from antibiosis and tolerance
• The resistance would be adequate to protect Canadian spring wheat under most circumstances
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Wheat midge
Bread wheat
Durum wheat
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Oviposition deterrence in durum wheat
Choice No choice
Eggs
/ sp
ike
0
5
10
15
20
25
30
'Kahla 47''AC Avonlea'
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Oviposition on resistant and susceptible wheat
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Antibiosis in wheat with the Sm1 gene
• Inducible hypersensitivity
• Increased levels of ferulicand p-coumaric acids
• Levels drop to normal at seed maturity
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Inheritance and expression of resistance
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Antibiosis
• Controlled by a single gene - Sm1
• Resistance is partly dominant
• Same gene in all known resistance sources
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Antibiosis in spring wheat
The fact that antibiosis is due to a single gene means that:
• It is readily incorporated into breeding programs.
• It is likely that virulent midge will evolve to overcome the resistance.
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Terms
Wheat plantresistant – antibiotic to midgesusceptible – not antibiotic to midge
Wheat midgevirulent – adapted to resistant wheatavirulent – not adapted to resistant
wheat
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Could wheat midge develop virulence?
• Evolution of virulence occurs in other pest-crop systems
• On resistant wheat, 1 mature wheat midge larva per 175 spikes
• The occasional larva is within the size range of larvae from susceptible wheat
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Hessian fly resistance gene, H3(from Foster et al. 1991)
Year%
Acreage%
Infestation(H3)
%Infestation
(susceptible)1956 <1 <1 29
1960 35 <1 15
1964 74 2 6
1965 80 9 10
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Managing crop resistance
• Sequential release of resistance genes
• Pyramiding resistance genes
• Provide a refuge for avirulent insects
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Using refuges to delay virulence evolution
Deploying refuges:
• Plant in separate, adjacent blocks.
• Mix with resistant plants so susceptible plants are interspersed.
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Using refuges to delay virulence evolution
Separate blocks or interspersed mixtures?
• Ensure that mating is random among genotypes.
• Larvae on resistant plants must not be able to move to susceptible plants.
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Deploy crop resistance with a susceptible refuge
- minimize damage
- eliminate insecticides
- preserve resistance
- preserve parasitism
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With and without interspersed refuges in large field plots
% susceptible wheat0 5 10 15 100
% m
idge
-dam
aged
see
d
0
4
8
12
16
20
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Conclusions:
Resistance against wheat midge possible
An interspersed refuge can protect the resistance gene