IDENTIFYING THE KEY-STAGES OF RHIZOCTONIA SOLANI AG-3 PT EPIDEMICS: A CRUCIAL STEP IN DEVELOPING INTEGRATED

CONTROL STRATEGIES

Bouchek-Mechiche K1, 2, Buisson C1, 2, Navier H1, 2, Mille B1 & Andrivon D1

1) UMR IGEPP, INRA/ BP 35327, 35653 Le Rheu Cedex, (2) GNIS, 44 rue du Louvre, 75001 Paris, France

CASDAR

The aims of the study

Karima Bouchek

I. To describe the disease progress curves on different potato

organs from planting until harvest & to provide overall picture of

the disease complex

II. To characterize the epidemiological traits of the pathogen

● infection rate and its modulation by T° and plant age

● disease spread within plants

INTRODUCTION Diversity in symptoms on potatoes

Stem and stolon canker Early sprout cutting

Corky blemishes Black scurf

Different AGs of R. solani isolated from potatoes in France (2009-2011)

Number of isolates per AG

Geographical origin AG 3 PT AG 5 AG 2-1

Brittany

Finistère 148 - 10

Morbihan 16 - -

Côtes-d'Armor 3 - -

Other origins

Pas-de-Calais 43 - -

Somme 10 - -

Eure 3 - -

Eure-et-Loir 1 - -

Loiret 2 5 -

Total 226 5 10

(Fiers et al, 2012)

INTRODUCTION Diversity of R. solani isolates in France

The soil was inoculated with infested barley seeds by R. solani AG3 PT

• 3 grams of contaminated barley around each seed tuber

2 potato varieties considered as susceptible (Nicola) and less susceptible

(Sirtema or V2)

Randomized blocks with 4 repetitions

Plants were harvested sequentially at weekly intervals

• 24 plants were harvested/variety/sampling date

• Plants were scored visually for :

- stem and stolon cankers,

- corky blemishes and black scurf on daughter tubers

- incidence and severity were calculated

I. Monitoring the kinetics of symptoms development in the field

Important items of materials & methods

2010 2011 2012

wheat

Monitoring the kinetics of symptoms development:

field experiments

Experimental design 2010 - 2012

Sirtema Nicola Nicola Sirtema V-2 Nicola Nicola V-2

Monitoring the kinetics of symptoms development:

field experiments

Results 2010 Disease progress curves on different organs of susceptible variety Nicola

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1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 10 W 12 W 14 W 16 W 17 W 18 W 19 W 20 W

Incid

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Harvest dates

Sirtema Nicola Nicola Sirtema

Stem canker : high incidence was observed at emergence

The stolons became diseased just after their formation (3 weeks after planting)

Corky blemishes appeared at tuber initiation, their incidence increased over time

Sclerotia , appeared at the end of the vegetation period and as expected, their incidence and severity increased fast after haulm destruction.

Monitoring the kinetics of symptoms development:

on two varieties

Results 2010

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1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 10 W 12 W 14 W 16 W 17 W 18 W 19 W 20 W 21 W

Incid

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Harvest dates

Disease progress curves on Nicola & Sirtema

Nicola

Sirtema

Sirtema Nicola Nicola Sirtema

The disease progress curves of different symptoms are similar on the two varieties

Monitoring the kinetics of symptoms development:

with different inoculum levels

2. Incidence of black scurf over time

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1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 10 W

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Nicola-inoc Nico-non-inoc

V2-inoc V2-non-inoc

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1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 10 W

Nicola-inoc Nico-non-inoc V2-inoc V2-non-inoc

1. Incidence of stem canker over time

Inoculated

Non- inoculated

Inoculated

Non- inoculated 0

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1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 10 W

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V-2-inoc V-2-non-inoc

3. Incidence of corky blemishes over time

Results 2012 V-2 Nicola Nicola V2-

Nicola V-2 V2- Nicola

Effect of level of soil inoculum on the development of stem cankers and black scurf, the two varieties behave the same

II. Assessment of epidemiological traits of R. solani AG-3 PT

under controlled conditions

The effect of temperature and plant age on the rate of infection

The disease spread within and between plants

Effect of the temperature on pathogen infection and on the

fungus growth

1.Effect of the T° on the incidence of stem canker

2. Effect of the T° on the AG-3 growth in-vitro

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W1 W2 W3 W4

Incid

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Time (weeks)

23°/25°

8°/10°

emergence

emergence

In growth chambers : seed tubers planted in infested soil and pots were put to growth at different temperatures Growth in-vitro: Petrie dishes with mycelium plug placed in different T°, the mycelial growth recorded

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20 °C

10 °C

•Temperature affects the plant development and he fungus growth • Black scurf on daughter tubers was observed in all temperatures tested but high incidence and severity were obtained at 18/20°C (data not shown)

The main elements of Materials & Methods

Results

Effect of the plant age on infection

Inoculum: contaminated millet grain Inoculation : at different ages of the plant

Scoring : incidence et severity of stem cankers, black scurf on daughter tubers at harvest

Inoculation at different ages of the plant

plantation

0W 2 W 4W 6W 8W 10W 12W Haulm kiling

Harvest

The main elements of Materiel & Methods

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W-0 W-2 W-4 W-6 W-8 W-10 W-12

se

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rity

Plant ages at inoculation time (weeks)

Black scurf

Stem canker

• The severity of stem cankers decreased with plant age

• The severity of black scurf on daughter tubers was high whatever the inoculation date

Karima Boucher-EAPR-Jerusalem -2013

Effect of plant age on stem and tuber infections

• Soil inoculum produce the primary infection which initiate the disease

• Secondary inoculum plays an important role on disease spread between potato organs

The disease spread within plant

• Contaminated tubers were harvested from field experiment two weeks after plantation • Tubers were washed and transplanted into pots filled with sterile soil mixture (sand and peat) • The different symptoms were scored over time

Results

The main elements of Materials & Methods

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W-0 W-1 W-2 W-3 W-4 W-5 W-7 W-9 W11 W12 W13 W14 W15

Inci

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Haulm killing

Stem canker

Stolon canker

Black scurf

Incid

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rity

Conclusion

Different sources can transmit the pathogen

Potato is susceptible in all its life cycle & all its organs are sensitive

Susceptibility of cultivated varieties

A wide range of temperatures are conducive to R. solani diseases

Spread of the disease within and between plants

I. The main epidemiological traits of R. solani

II. Development of integrated control strategies, but before we need to :

understand the mode of action of existing and or/ innovative methods

Know how to combine them (complementary, additive, compatible methods)

Design and experiment integrated itineraries in different production systems

III. How we may deal with corky blemishes?

Difficulties for isolating the pathogen(s)

Difficulties in reproducing symptoms

Different causes but similarity in symptoms

Thank you !