Powdery scab in France

Past and current research

Karima Bouchek-Mechiche1,2, Catherine Chatot 3 &

Yves Le Hingrat1

1 French Federation of Seed Potato Growers

2 INRA -IGEPP

3 Germicopa

1

Powdery scab studied as part of a potato tuber blemishes program

Rhizoctonia R. solani

Silver scurf H. solani

Black dot C. coccodes

Powdery scab S. subterranea

Common and netted scab * CS : S. scabies et Streptomyces spp. * NS: S. reticuliscabiei

5 pathogens/diseases studied

Objective : How to manage several soil-borne pathogens together?

Powdery scab context

• Powdery scab is not a major problem in French potato production areas

• French certification threshold is 0.2% infected tubers

• Occasional contamination in fields and peat or other culture substrates

– Main question : what is the origin of the contamination, remaining unsolved so far ?

PS activities over time

• Diagnostic & detection tools

2000-2003

• Cultivar assessment trials

2004-2005

• Epidemiology trials

2008-2010

• Improving soil detection

• Epidemiology

2016-2018

Objective 1 : Avoiding new introductions and dissemination of Sss

From tubers

ELISA Test AgriStrip

TaqMan/PCR PCR/Nested PCR

Development of detection tools

From soil

tomatoes

Tomato roots

PCR

Baiting test

TaqMan-PCR

diseased

Not yet achieved

AgriStrip is helpful for the diagnosis

Lots Symptoms Type Sss

AgriStrip

qPCR

Sss

Streptomyces

marquers

1

2

3

4

PS

PS

PS

PS

Typical

Typical

Typical

Typical

+

+

+

+

+

+

+

+

-

-

-

-

5a

5b

6a

6b

7a

7b

PS

?

PS

?

PS

?

Typical

Atypical

Typical

Atypical

Typical

Atypical

+

+

+

+

+

+

+

+

+

+

+

+

-

-

-

-

-

-

8

9

10

11

12

13

14

15

16

17

?

?

?

?

?

?

?

?

?

?

Atypical

Atypical

Atypical

Atypical

Atypical

Atypical

Atypical

Atypical

Atypical

Atypical

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

+

+

+

+

+

+

+

+

+

+

18

19

CS

CS

Typical

Typical

-

-

-

-

+

+

Efficient detection of S. subterranea

Atypical powdery scab symptoms

PCRq=+ AgriStrip = +

PCRq=+ AgriStrip = +

PCRq=+ AgriStrip = +

PCRq=+ AgriStrip = +

PCRq=+ AgriStrip = +

Atypical common scab symptoms

Web site potato tuber blemishes

http://www.potato-tuber-blemishes.com

Objective 2. Studying the risk of PS development under French conditions

Are French environmental conditions conducive to powdery scab?

3 years trials 2008, 2009 2010

Contaminated field

Measures

Air T° and rainfall, soil humidity

Scoring roots for galls and tuber for powdery scab At tuber initiation and each 15 days intervals

Two varieties Nicola & Kennebec

Powdery scab expression in 2008

Powdery scab observed early after tuber initiation

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90

21 may 10 july 17 july 24 july 31 july 07 august 18 august 18 september

Se

ve

rity

(in

de

x)

incid

en

ce

(%

)

prélèvements

incidence and severity of PS over the season

Kennebec incidence Nicola incidence

Tuberisation

P1

No galls observed on roots

Powdery scab expression in 2009 & 2010

-1

1

3

5

7

9

11

13

15

0

10

20

30

40

50

26 june 06 july 16 july 21 july 28 july 3 august 11 august 10 september

Ind

ex

inc

ide

nce

Sampling

2009

Kennebec incidence Nicola incidence Kennebec Index Nicola Index

harvest

0

2

4

6

8

10

12

0

20

40

60

80

100

28 june 05 july 12 july 19 july 26 july 2 august 11 august 09 september

Ind

ex

Inci

den

ce

Sampling

2010

Kennebec incidence Nicola incidence Kennebec index Nicola index

Tuberisation

Tuberisation

Rainfall & tuberisation during the three years trials

Tu

beri

sa

tio

n

20

09

/20

10

Tu

beri

sa

tio

n 2

00

8

0

10

20

30

40

50

60

70

80

90

d1 d2 d3 d1 d2 d3 d1 d2 d3 d1 d2 d3 d1

mai mai mai juin juin juin juillet juillet juillet aout aout aout sept

Rain

fall

(m

m)

2008

2009

2010

0

2

4

6

8

10

12

14

28-mai 04-juin 11-juin 18-juin 25-juin 02-juil. 09-juil. 16-juil. 23-juil. 30-juil. 06-août 13-août 20-août

Soil

hu

mid

ity

(b

ar)

Y 2010

Y 2009

Dry period

Summary of the main data for PS expression

Years 2008 2009 2010

Plantation date 22/05 05/05 12/05

Tubérisation 10-17/07 26/06 28/06

Precipitations around tuber

initiation period

97,5 28.5 28

Temperatures at tuber initiation 15.5 16 16

Mean T° during the trial 16 °C 18,5 16.5

Total of precipitation during the

trial

394 mm 265 mm 290 mm

Powdery scab incidence 22-81% 3-7% 10-38%

Objective 3 : Assessing the behaviour of potato varieties

2 years trials 2005 & 2006

Scoring At harvest for powdery scab on tubers

One month after planting for root galls

Susceptibility of French cultivars

Number of cultivars tested 2005: 15 2006: 21 References varieties in both trials: 7

Susceptibility of French varieties Incidence *

*Standard varieties

Different ranging in 2004 and 2005

0

10

20

30

40

50

60

70

80

90

100

110

Incid

en

ce

Varieties

Y 2004

Y 2005

* *

*

Less susceptible Moderately susceptible

Susceptible

* * *

Susceptibility of the varieties Severity

* *

0

1

2

3

4

5

6

7

8

9

Dis

ea

se

in

de

x

Varieties

Y 2004

Y 2005

Susceptible

Moderately susceptible

Less susceptible

*

* Control cultivars

* * * * *

Sclerotia of R. solani on roots

No powdery scab galls were observed on roots

Susceptibility of the varieties

Susceptibility to other potato blemishes

0

2

4

6

8

10

12

14

16

18

20

Rosanna Lady Roseta Nicola gladiator Désirée Estima Saturna Agria Kennebec

Sca

b i

nd

ex

Powdery Scab

Rhizoctonia

common scab

Gladiator with common scab and few powdery scab

Gladiator with Rhizoctonia solani

Susceptibility to other potato blemishes

Conclusions

The French certification standard is severe in order to avoid the dissemination of the pathogen in the territory

AgriStrip ® is an efficient tool to distinguish PS symptoms from CS, it helps the certification procedure

Detection tools are very efficient to detect the pathogen from tuber and plant roots but not optimal for routine detection directly from the soil

The French environmental conditions may be favorable to PS if soils become contaminated

The French varieties are classified in different categories ranging from susceptible to fairly resistant

Ongoing research

Develop detection tools for soil and other substrates samples (peat, other …)

Routine test

Understand the origins of the contamination in the substrates

Develop a routine test to screen different control methods (eg: biocontrol), particularly to secure the quality of early seed generations

Objectives are to :

Thank you for your attention !