Epidémiologie et dispersion de maladies - (dans des associations variétales de blé)
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Epidémiologie et dispersion de
maladies
(dans des associations variétales de blé)
Sébastien Saint-Jean
mardi 21 avril 2020
UMR « EcoSys »
Écologie fonctionnelle et écotoxicologie des agroécosystèmes
AgroParisTech & INRAE, Thiverval-Grignon
Sebastien.Saint-Jean@AgroParisTech.fr
Disclainer
The following story is
fictionnal
and does not depict any
actual person or event
World War Z
Context
• In a changing global context (demographic growth, climate change,
environmental awareness, pandemic)
Agricultural systems need to adapt and to provide a stable food
production
• Interests of agricultural biodiversity:
– complementarity, facilitation
– improved used of resources (ex: light, water, nitrogen)
– reduced susceptibility to multiple (a)biotic stresses
• Disease management:
– high potential yield loss
– limits of main management techniques
– Fungicides: resistance of pathogens, environmental impacts
– Genetic resistance of cultivars: breakdown of resistance genes
→ need for complementary management techniques
Context
The earth’s atmosphere is full of miasma
P. H. Gregory (1973)
Focal dispersal: Wheat Rust
Pure stand
Mixture
de Vallavieille-Pope & Goyeau, 1997
Dispersal Gradient/GUA
Cultivar mixtures Spatial scale of the host
(GUA = Genotype Unit Area)
(From Garrett & Mundt, 1999)
Large Small
Deep
splash-
(short distances)
dispersal
Dispersal
gradient
wind-EFFET DES PARAMETRES
Shallow DES MALADIES
dispersal (long distances)
SUR LE SCHEMA DE DIVERSIFICATION
gradient de dispersion
Dispersal Gradient/GUA
(From Garrett & Mundt, 1999)
Downloaded from http://rsif.royalsocietypublishing.org/ on February 4, 2015
(d) 3
splash on film
Figure 1.12(a) – Photo d’un couvert végétal dans un herbier de zostères marines
rsif.royalsocietypublishing.org
(Zostera marina) (Tigani, 2006).
Deep
splash-
(b) (c)
(short distances)
dispersal
J. R. Soc. Interface 12: 20141092
Rain (Gilet et al 2015)
Figure 2. Ejection of contaminated droplets (highlighted in red) triggered by the impact of a raindrop (diameter 2.5 mm, velocity 6 m s21) on (a) a green liquid
film (here in a 1 mm depth pool at the upper surface of the cantilever beam) at 22.5, 2.5, 17.5 and 62.5 ms after impact; (b) a prayer plant leaf at 6 ms after
Dispersal impact; (c) a strawberry leaf at 55 ms after impact; (d ) a lucky bamboo leaf at 22, 4, 8, 16, 52, 61, 69 and 74 ms after impact. In (b – d ), a sessile drop containing
pathogen analogue (red dye) is initially placed close to the impact point. Scale bars, 1 cm. See electronic supplementary material, movies S1– S4.
gradient film and wet leaf configurations, a liquid sheet is formed then size and initial position) that are simultaneously varied in
fragmented into several ejected droplets. Nevertheless, both natural conditions. Nevertheless, these many modes of patho-
configurations have markedly different outcomes. On a film, gen-bearing droplet ejection are not equally likely, nor are
the liquid sheet is more or less vertical and axisymmetric they equally good at ejecting droplets away. Only scenarios
about a vertical axis, and so is the droplet ejection (figure 2a). that are both likely and efficient can potentially govern the
On real plants, the liquid sheet is observed to be asymmetric, dynamics of rain-induced pathogen dispersal shaping epi-
wind- Shallow which typically gives a strong horizontal velocity to the ejected
droplets (figure 2b,d). Moreover, additional ejection scenarios
demic growth in the field. We recorded and analysed high-
speed visualizations (Phantom-v5, 1000 frames s21) of thou-
dispersal
are present on real plants that do not involve the fragmentation sands of raindrops in the millimetre range impacting on 30
(long distances) of a sheet (figure 2c,d).
The difference between the conjectured and the observed
plants, including foliar disease victims (figure 2b–d). The leaf
initially supported a sessile dyed drop, which was used as the
scenarios originates from the wetting properties of plant analogue of an infected drop. The visualizations indeed
leaves. Contact angles were found to vary between 608 and revealed a collection of liquid fragmentation phenomena, all
Wind (Gosselin., 2009)
1208 on 13 common plant leaves [38]. So the leaves are not
totally hydrophilic and the formation of a water film on the
very different from the splash on a liquid film (figure 2a)
[37,41]. We identified two dominant modes of droplet ejection.
leaf surface is not energetically favourable. This partial wet- In the first ejection mode, the raindrop impacts in the vicinity
ting behaviour is thought to minimize disturbance to plant of the dyed sessile drop and expands until direct contact between
breathing and structural stability. Moreover, it reduces detri- them occurs (figures 2b,d and 3a–b). Subsequently, the raindrop
mental colonization of the leaf surface [39]. Contact angle slides underneath the dyed drop. The latter is then lifted in suc-
hysteresis up to 308 has been observed, which is consistent cession in the form of a sheet that fragments into filaments and
with other recent measurements on common plants (e.g. droplets. We refer to this mode as the crescent-moon splash due to
[40]). The corresponding surface tension forces at the contact the shape and motion of the liquid sheet. Leaf compliance
lines prevent small droplets from sliding away, so the rain- has little qualitative influence on this mechanism (figure 3a
water residuals from previous impacts accumulate on the versus b). The crescent-moon splash shares certain features
leaf. Large drops and puddles drip off when this force with liquid splashes commonly described in the literature
induced by contact angle hysteresis no longer balances the (e.g. corona splash [37]). These include the dynamics of initial
pull of either gravity or wind drag. Leaf compliance mag- raindrop spreading. However, the horizontal asymmetry of its
https://www.nejm.org/doi/10.1056/NEJMicm1501197
Size matters
Particle Settling Rate ( release height 1.5 m)
0.5 µm 1 µm 3 µm 10 µm 100 µm
41 hours 12 hours 1.5 hours 8.2 minutes 5.8 seconds3D structure of a wheat-like canopy with 2 cultivars
Vidal et al Plos 2017Disease potential progression
90
80
Initial Cycle 1 Cycle 2 Cycle 3 70
Highly state
Resistance %
60
susceptible
50
pure stand
(5%) 40
30
Moderately
20
resistant pure
stand 10
( 50%)
Highly Comparatively to the mean
resistant pure of the pure stands, the
stand progression of disease
(90 %) potential within the mixture
was globally reduced by 35%
Mixture of the
three cultivars
after three dispersal cycles.
(in equi-
proportion)
➠ Consistent with field work (Gigot et al. 2013)CLE IN PRESS
ng and Environment 41 (2006) 1691–1702 1697
are
n to
(7)
mly
the
(8)
Fig. 7. Scalar velocity distrbution in Case 1 (m/s): (1) in section
ABCD; (2) in region A (enlarged).
(9)
m in
that
h at
wallARTICLE IN PRESS
S.W. Zhu et al. / Building and Environment 41 (2006) 1691–1702 1699
Fig. 11. Saliva droplets’ dispersion (simulation results of Case 1): (1) D ¼ 30 mm; (2) D ¼ 50 mm; (3) D ¼ 100 mm; (4) D ¼ 200 mm; (5) D ¼
300 mm; (6) D ¼ 500 mm.Settling velocity
102
101
100
Settling velocity (m/s)
ng
10-1
ttli
Se
Di
ffu
sio
10-2
n
10-3
10-4
10-2 100 102
Particles diameter (µm)Mechanisms involved in disease severity reduction
Cultivar mixtures
Pure stands
Cultivar mixture
Barrier effect
Rice cultivar mixture: to Density effect
control Magnaporthe
grisea (Finckh, 2008) Premunition effectWind and focal dispersal: Wheat Rust
Pure stand
100
80
Susceptible cultivar
Severity %
60
Mixture (1: 2)
40
20
0
6 7 8 9 10 11 12 13
Week after innoculation
Mixture effect: 57% Mixture
de Vallavieille-Pope & Goyeau, 1997Progression de la surface verte
Progression de la surface
verte à l’échelle des trois
dernières feuilles post
épiaison
N13 = 13 juin
Effet association : ralentit progression de la sénescence
induite 20Proportions and difference in resistance levels
Emax = f( proportions, resistance difference, spatial
organisation )
100
80
Maximal protective
100 (100-0)
90 (95-5)
Difference between
effect (Emax)
80 (90-10)
60 70 (85-15) resistance levels (R-S)
60 (80-20)
40 50 (75-25)
40 (70-30)
30 (65-35)
20 20 (60-40)
10 (55-45)
0 (50-50)
0
1/9 2/8 3/7 4/6 5/5 6/4 7/3 8/2 9/1
Susceptible cv /Resitant cv ProportionsUmbrella effect
l The amount of drops
intercepted by a leaf layer
depends on the leaf area
0
above this leaf layer
each leaf layer
1
LAI above
2
3
R 4
5
0 10 20 30 40
S Intercepted raindrops
(% of total raindrops, per m² of leaves)Umbrella effect
l The amount of drops
intercepted by a leaf layer
depends on the leaf area
0
above this leaf layer
each leaf layer
1
LAI above
2
3
R 4
5
0 10 20 30 40
S Intercepted raindrops
(% of total raindrops, per m² of leaves)Height effect
l The amount of inoculum intercepted by
a leaf layer strongly depends on the
1.2
height to the main inoculum source
1.0
Distance to the
inoculum source
(height, m)
0.8
0.6
0.4
0.2
0.0
S
-0.2
0 2 4 6
Intercepted inoculum
R (contamination units per 100 drops
and per m² of leaves)
Interception by resistant leaves → barrier effectConclusion (d’après confinement)
• Durabilité des résistances
• Thèses de Carolina Orellana et Stage M2 de Jérome Lageyre
Frédéric Suffert et Tiphaine VidalPure stands
t0 t1 Asexual multiplication t2 Sexual reproduction t0’
(year n) (year n+1)
No filter effect Recombination
Virulent (avr)
Avirulent (Avr)
SPure stands
t0 t1 Asexual multiplication t2 Sexual reproduction t0’
(year n) (year n+1)
No filter effect Recombination
Virulent (avr)
Avirulent (Avr)
S
Filter effect Recombination
RCultivar mixtures
t0 t1 Asexual multiplication t2 Sexual reproduction t0’
(year n) (year n+1)
Inter-cv
Filter effect spore transfer Recombination
Virulent (avrStb16q) S R Splashing
Avirulent (AvrStb16q) Stb16q Stb16q
Dilution effect
Barrier effectCultivar mixtures
t0 t1 Asexual multiplication t2 Sexual reproduction t0’
(year n) (year n+1)
? !′"
Inter-cv
!" Filter effect spore transfer Recombination
Virulent (avrStb16q) S R
Avirulent (AvrStb16q) Stb16q Stb16q
Dilution effect
Barrier effect
S: R: Cellule
Apache 100 75 50 25 0%
Stb16
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