introduction : alb and quantitative resistance experiment ......cv1 cv2 well-studied resistance...
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Is quantitative resistance qualitative ? An example with two Alternaria leaf blight resistant carrot genotypes and four resistance assessment techniques.
Introduction : ALB and quantitative resistance
Experiment setup
Comparing four resistance assessment methods
Conclusion
ALB and quantitative resistance
Alternaria Leaf Blight
Coalescing gray-brown lesionsCoalescing gray-brown lesionsBurnt aspect of severely affected leaves
Most destructive foliage disease,caused by Alternaria dauci
ALB and quantitative resistance
Vertical resistanceQualitativeStrain-specific
Horizontal resistanceQuantitativeNon strain-specific
Disease severity CV1 CV2
Well-studied resistance mechanisms(NBS-LRR proteins, etc.)
Mendelian determinism
CV1 CV2
Only partially uncoveredresistance mechanisms
Quantitative determinism(QTLs)
Disease severity
1 2 3 4 1 2 3 4
Strain
1 2 3 4 1 2 3 4
Strain
ALB and quantitative resistance
Vertical resistanceQualitativeStrain-specific
Horizontal resistanceQuantitativeNon strain-specific
ALB resistance is horizontal
No complete resistance is known
Current cultivars show insufficient levels of resistance
Disease severity CV1 CV2
Well-studied resistance mechanisms(NBS-LRR proteins, etc.)
Mendelian determinism
CV1 CV2
Only partially uncoveredresistance mechanisms
Quantitative determinism(QTLs)
Current cultivars show insufficient levels of resistance
→ How to measure horizontal resistance ?
Resistance sources are found in different germplasms
→ Are they really different?
Disease severity
1 2 3 4 1 2 3 4
Strain
1 2 3 4 1 2 3 4
Strain
Is quantitative resistance qualitative ? An example with two Alternaria leaf blight resistant carrot genotypes and four resistance assessment techniques.
Introduction : ALB and quantitative resistance
Experiment setup
Comparing four resistance assessment methods
Conclusion
Experiment setup
ALB resistance is horizontal
No complete resistance is known→ How to measure horizontal resistance ?
Current cultivars show insufficient levels of resistance
Resistance sources are found in different germplasms
→ Are they really different?
∙ Standard visual assessment (DS evaluation)→ Time consuming, environmental effects, evaluator effect…
Three alternative methods tested :
∙ qPCR
∙ In vivo spore germination∙ In vivo spore germination
∙ drop inoculation
Three cultivars : ∙ Presto (S) ∙ Bolero (R1) ∙ Texto (R2)
Two strains : ∙ A2 ∙ P2
Experiment setup
Dropinoculation
Spray inoculation
Disease Severityevaluation
Real-TimePCR
Conidiagermination
Symptomnumber
Experiment setup
Non detached leavesIncubation chambers: higher moisture
Pre-defined drop volume (5µL)Pre-defined drop volume (5µL)Pre-defined drop number (40)
Total number of A. dauci spores is known from inoculumconcentration
Symptom counting:A more objective notation.
Is quantitative resistance qualitative ? An example with two Alternaria leaf blight resistant carrot genotypes and four resistance assessment techniques.
Introduction : ALB and quantitative resistance
Experiment setup
Comparing four resistance assessment methods
Conclusion
Four evaluation methods
Presto (S)Bolero (R1)Texto (R2)3
Disease index
2
1
Disease index
P2 A2
10 15 20 25
Days Post-Inoculation
Presto always shows stronger disease indexes thanresistant cultivars
Maximum difference observed at 15 dpi.
No observed strain-cultivar interaction
Four evaluation methods
Presto (S)Bolero (R1)Texto (R2)100
Infe
ction R
atio
1
10
0,1
Infe
ction R
atio
A2 P2
0 10 15 25
Days Post-Inoculation
Presto shows stronger infection ratio thanresistant cultivars after 10 dpi
Maximum difference observed at 15 dpi.
No observed strain-cultivar interaction
5 20
Four evaluation methods
4
Mean G
erm
tube N
um
ber Presto (S)
Bolero (R1)Texto (R2)
2
3
1
Mean G
erm
tube N
um
ber
0
Germination rate ≃100%,∀ tested cultivar
0P TB
Example on Texto : 7 germ tubes
large germ tube numbers on resistant cultivars = failed penetration attempts?
Four evaluation methods
Presto (S)Bolero (R1)Texto (R2)
100
/ 100 sp.
200 sp/mL 1000 sp/mL
1
10
Nb
Sym
pt/ 100 sp.
7 13 7 13
Days Post-Inoculation
Fine tuning of the experiment: Spore concentration, inoculation date, notation date, etc.200 sp/mL: Resistance is detectable in Bolero compared with Presto. Texto shows intermediate resistance levels
9 9
Presto (S)Bolero (R1)Texto (R2)
100
/ 100 sp.
200 sp/mL 1000 sp/mL
Four evaluation methods
1
10
Nb
Sym
pt/ 100 sp.
7 13 7 13
Days Post-Inoculation
9 9
Fine tuning of the experiment: Spore concentration, inoculation date, notation date, etc.1000 sp/mL quite different results: More symptoms in Texto than Presto! What happened?
Four evaluation methods
Presto
13 dpi, 1000 sp/mL
Bolero
Four evaluation methods
13 dpi, 1000 sp/mL
Texto
Is quantitative resistance qualitative ? An example with two Alternaria leaf blight resistant carrot genotypes and four resistance assessment techniques.
Introduction : ALB and quantitative resistance
Experiment setup
Comparing four resistance assessment methods
Conclusion : Qualitative resistance variation
Conclusion
Better resolution of the resistance level
Faster evaluation of resistance level (1dpi)
Observed resistance level is influenced by the evaluation method
When comparing resistance levels, homogeneity of evaluation method is critical.
Smaller sample needed
of resistance level (1dpi)
Different evaluation method uncover different resistance mechanisms
method is critical.
Comparing two resistances
R
Bolero / Presto: Bolero always significantly more resistant.Texto: Strong effect of the evaluation method.
Acknowledgments
Cora BOEDOMickaël LECOMPTE
Stéphanie BERSIHANDSabrina MARQUESSabrina MARQUESPascal POUPARDMathilde BRIARDValérie LE CLERC
Philippe SIMONEAU
Bruno HAMONAnita SUEL
Jacky GRANGERRémi GARDET FCE GrantRémi GARDET FCE Grant
CVP Project2007–2010
CIFRE GrantClause Vegetable
Seeds