Aggressiveness and transmission : does a correlation exist in

P. infestans ?Pasco C., Marquer B., Douchy H., Magalon H. and Andrivon D.

Workshop Hamar, Norway 28-31/10/2008

Rationale

Using resistant cultivars- useful alternative to pesticides…- … only if resistance is durable/ stable

which supposes that aggressiveness doesnot continually increase over time.

Andrivon et al., 2007

üAggressiveness increases during epidemics

Is aggressiveness stable ?

üEuropean populations are polymorphic for aggressiveness

UK – Day & Shaw 1999; Ireland – Gillian & CookeF - Lebreton et al. 1999; Pilet et al. 2003; Montarry et al. 2006NL – Flier et al. 1999

Þ this implies that selection for higher aggressiveness is possible

Ü Consequences in the long run ?

Sporangia production/lesion

0

20000

40000

60000

80000

100000

beginning of theepidemic

end of the epidemic

Consequences : possible scenariosIf high aggressiveness does not lead to a decrease in season-to-season transmission

Þ gradual increase in mean aggressiveness over time

Resistanceerosion

Stableaggressiveness

epidemic survival epidemic survival epidemic survival

If high aggressiveness leads to a decrease of transmissionÞ Aggressiveness should remain stable

• Asexual transmission between seasonsÞ three successive steps

High aggressiveness

Few and small tubersHigh infection

High rotting proportion

High death rate of stems

Poor transmission

Low

aggressiveness

Many and big tubersLow infection

Low rotting proportion

Low death rate of stems

Goodtransmission

Why could there be a trade-off ?

2. Winter survival

3.

Émission de repousses malades

3.

Émission de repousses malades

3. Emergence of diseased

stems

1. Transmission from leaves to

tubers

What do we know today ? AB B B

0

0,2

0,4

0,6

0,8

1

1,2

Sur

viva

l rat

e

Control Low Ai Middle Ai High Ai1. Transmission from leaves to

tubers

2. Survival winter

Émis repo ma

Émis repo ma

3. Emergence of death

deseased stems

High aggressiveness

Few and small tubersHigh infection

High rotting proportion

High death rateof stems

Poor transmission

Low

aggressiveness

Many and big tubersLow infection

Low rotting proportion

Low death rateof stems

Goodtransmission

Montarry et al. 2007Funct Ecol

Part 2

Part 1Aggressiveness

Part 1Tubers to foliage

transmission

1 – Tubers to foliage transmission

- 3 isolates of Phytophthora infestans with ≠ agressiveness on leaflet of cultivar Bintje

- Tubers - One susceptible cultivar : Bintje

- 100 tubers per isolate (repetition)

- water control (sterile water)

S1 S2 S3

Inoculation method

tubers were placed in humid chamber for 3 days at 18°C

Opening lenticels

Sporangia suspension is produced on detached leaflets

Tubers were kept in humid

chamber for 4 days

Planting in compost

Spray inoculation : 5x104

sporangia/tuber

Emergence notation : one month after planting

Control S1

S2 S3

100 % 51 %

67 % 18 %Lowest emergence rate :

Stem blight 36 days after planting

+ 15 days

Some symptoms of stem blight

Some other symptoms observed

aerial tubers

very premature stem death

Scorings -% Emergence

-Stem number per plant

- Number of diseased stems per plant

Two years : 2007 & 2008

ResultsHigher aggressiveness results in:

Þ fewer emerged plants, Þ fewer stems per plant,

butÞ no differences in the proportion of blighted stems among those emerged

Overall :

transmission of the most aggressive isolate is less efficient

Trade-off between aggressiveness and

transmission

Number of emerged plants

0

20

40

60

80

100

120

Témoin S1 S2 S3

A

B B

C

Control

00,0050,01

0,0150,02

0,0250,03

Témoin S1 S2 S3

Proportion of blighted stems

A

BB B

Control

Average number of stem by plant

0123456789

Témoin S1 S2 S3

A

B B C

Control

Foliage to tubers transmission

Part 2

Method - 3 Phytophthora infestans isolates with ≠ agressiveness on cultivar Bintje foliage

- One susceptible cultivar : Bintje

- Plants at different stages of their growth D1 D2 D3

- 10 plants per isolate and per date

- water as a control

S1 S2 S3

MethodPlants were grown in greenhouse 15-20°C, 16 hours of day : 3

planting dates

Transfer into chapels outside

1 chapel per isolate, with

-10 plants Date 1 (72 days)

-10 plants Date 2 (56 days)

- 10 plants Date 3 (42 days)

Þ Early to late epidemics

D1

D2

D3

Inoculation method

Inoculation : Distribute uniformly 20 drops of 20µl by plant.

Sporangia suspension is produced from infected detached leaflets

Let the symptoms develop on the foliage

Spray the foliage with water to wash

sporangia down towards tubers

Symptoms observed during the vegetation

Chlorosisnecrosis on petiole

Symptom at the end of the leafletSplashing on the leaves by rain

necroses at the plant top

Plants from Date 1 (72 days)18 days after inoculation.

Control

S1 S2

S3

1. Transmission from leaves to

tubers

LowAggressiveness

HighAggressiveness

What do we expect ?

Number and weightof tubers

Isolates aggressiveness did not influence

the mean number of tubers per plant.

their average weight.

Mean number of tubers per plant

1616,5

1717,5

1818,5

1919,5

20

T S1 S2 S3

A AA

A

Control

Mean weight of tubers per plant

0

10

20

30

40

50

T S1 S2 S3

A A A A

Control

Number and weight of blighted tubers

A

Isolates aggressiveness influence:

• the mean number of blighted tubers per plant

• their average weight.

Mean number of blighted tubers per plant

0

0,51

1,5

22,5

3

T S1 S2 S3

C BC

A

B

Control

Mean weight of blighted tuber per plant

0

10

20

30

40

50

T S1 S2 S3

A

C

BB

Control

To conclude

High Aggressiveness

Many small diseased tubers

High infection/ severity

High rotting proportion

High death rateof stems

Poor transmission

Low Aggressiveness

Fewer, bigger diseased tubers

Low infection

Low rotting proportion

Low death rateof stems

Goodtransmission

Þ A trade-off seems to exist between aggressiveness and transmission !

2. Survival winter

3.

Émission de repousses malades

3.

Émission de repousses malades

3. Emergence of diseased

stems

Part 11. Transmission from leaves to

tubers

Part 2

Where to now ?

• Check survival with tubers • of different sizes

• with different initial severity of blight

• Check the effect of tuber resistance

Thanks to

- Roselyne Corbière for the supply of isolates,

- Bruno Marquer, Hervé Douchy and Christian Guérin for their technical support,

- Didier Andrivon and Hélène Magalon to have helped me analyze these results and build this slide show.

Isolates Mean size lesion

Sporangia number /cm2

Sporangia number per lesion

S1S2S3

11.7814.3914.51

390514198667329

463000610766977983

Isolates aggressiveness tested on Bintje leaflets

Control S 1

Part 1 : Harvest, 50 days after planting

Notation at harvest : per plant- Number of tubers,

- Weight of tubers