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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
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