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