# Agroecology: biodiversity in agroecosystems to regulate pests and diseases?

Alexandra Jullien, Corinne Robert, Thierry Doré

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Alexandra Jullien, Corinne Robert, Thierry Doré. Agroecology: biodiversity in agroecosystems to regulate pests and diseases?. Conférence Internationale ANSES Impact du changement global sur l'émergence des maladies et des ravageurs des plantes en Europe, Apr 2018, Paris, France. hal-01799550

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# Agroecology: biodiversity in agroecosystems to regulate pests and diseases?

Jullien A.¹, Robert C.¹ and Doré T.²

¹ECOSYS, INRA, AgroParisTech, Université Paris-Saclay, Thiverval-Grignon, France

²Agronomie, INRA, AgroParisTech, Université Paris-Saclay Thiverval-Grignon, France

alexandra.jullien@agroparistech.fr
Context

At an international level:

- Yield plateau, and prediction of yield loss due to global warming (Wang et al., in press),

- Pesticides use is highly controversial due to their effects on environment and human health

At a national level:

- A long lasting reliance on pesticides, which does not drop: the IFT is approximately as high in 2017 as in 2008 (Starting Ecophyto 2018)

- Pesticides arsenal shrinks due to pathogens because of regulations and resistance

- New pests and diseases pop up due to global changes

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A need for alternative avenues – Agroecology as a solution ?

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XYLELLA FASTIDIOSA

Symptômes

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Symptômes peu caractéristiques

Brûlures foliaires, dessèchement des rameaux, mort de la plante dans les cas les plus graves (laurier-rose, olivier, amandier, chêne, orme...).

<figure><img src="image_11.png" /></figure>
Agenda of the talk

I. Agroecology and biodiversity

— What is agroecology?

- The key role of biodiversity in agroecology

II. Analysing the potential levers and mechanisms of pest and diseases regulation *via* biodiversity

III. Putting it all together: from mechanisms to agroecosystems including both ecological functioning and agronomic logic?

— Unknowns

- Trade-off
Part I

Agroecology and biodiversity
# What is agroecology?

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A large diversity of key-players ... with a wide range of acceptations for agroecology.

But for all of them, agroecology is a mean to re-create an alliance between agriculture, environment, science and society.

With shared core principles:

- Using **biotic interactions**, **self-regulations** and biodiversity rather than pesticides

- Exploiting non-renewable resources very carefully and **promote their recycling**

- Combining **indigenous** knowledge and **scientific** outputs

- Binding actions at different scales (plot-farm-lanscape-food system) to find solutions **ecologically**, **socially** and **economically** affordable

- Helping **famers** to find their own finely tuned systems

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# Agroecology : A new view on agroecosystems

**A key expectancy:**
**promoting self-regulations**

<figure><img src="image_19.png" /></figure>

**An approach:**
the agroecosystem seen as
different habitats with organisms
in interaction

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**A bet:**
**biodiversity and heterogeneity**
are levers to pests and diseases
self-regulation

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Médiène et al., 2011
# Some star systems in agroecology, which are already disseminating

## Conservation agriculture...

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## Agroforestry...

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- Refined by farmers experience and years of empiricism

- Locally conceived and adapted

- Complex and only partially studied by scientists

## Associations...

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=> limits to their generalisation

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Biodiversité, pests and diseases

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Bioagressors regualtion

Production

From Letourneau *et al.* 2011
Boudreau M., 2013
Poeydebat, 2016

* A major positive trend between biodiversity and pest regulation

* ✓ Fungii (75%) > nematodes and arthropodes

* What are the mechanisms underlying these global trend?

* Why is the effect variable?

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Part II

# Potential levers, mechanisms and effects at different scales
Different mechanisms for self-regulation of pests and diseases

<table><thead><tr><th>Process</th><th>Lever</th></tr></thead><tbody><tr><td><strong>Epidemics and attacks</strong></td><td></td></tr><tr><td>Dispersion</td><td>Density effect<br>Barrier effect</td></tr><tr><td>Infection</td><td>Premunition<br>Phylloclimat</td></tr><tr><td>Development of pathogens (nutrition, reproduction)</td><td>Ressources<br>Predators</td></tr><tr><td><strong>Plant response</strong></td><td></td></tr><tr><td>Escape, tolerance, compensation</td><td>Plasticity of the development</td></tr><tr><td>Resistance</td><td>Plant defence</td></tr><tr><td>Communication</td><td>Predators</td></tr></tbody></table>

Letournau *et al.*, 2011; Boudreau, 2013; Vidal *et al.*, 2018

How do **practices and biodiversity** trigger and drive these mechanisms?

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# Mobilizing plant-plant-organisms communication

## Mechanisms of the push-pull effect

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<figure><img src="image_36.png" /><figcaption>Pyrale & Striga (stemborer)</figcaption></figure>

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# Designing plant architectures for resilient crop

## At the plant scale : plant plasticity favours damage compensation

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## Related to plant capacity to produce secondary and primary branches

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<figure><img src="image_41.png" /><figcaption>Méligèthes
(Meligethes aeneus)</figcaption></figure>

Main stem

New primary axis

Termini

New primary inflorescence

<table><thead><tr><td></td><td>Low branching</td><td>High branching</td></tr></thead><tbody><tr><td>Low damage</td><td>Secondary</td><td>Secondary</td></tr><tr><td>High damage</td><td>Secondary</td><td>Secondary + Primary</td></tr></tbody></table>

scence

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Increasing damage
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# Designing plant architectures in mixed-crops

## At the canopy scale : mixing varieties of different heights to reduce epidemics

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« Umbrella » effect

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« Perchoir » effect

=> A tall susceptible variety in mixture with a short resistant one will reduce inoculum propagation of septoria tritici by rain splashing

Vidal, 2016

Vidal *et al.*, 2018, PlosOne

Vidal *et al.*, 2018 JExpBot

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Modified susceptible plant height

Fixed resistant plant height

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Decreasing the resources for the pathogens

**At the canopy scale : decreasing nitrogen fertilisation decrease epidemics**

Simulation of canopy growth and leaf rust epidemics for low and high crop fertilisation

Legend :

**Healthy**

**Latent**

**Sporulating** t1

**Dead**

Low fertilisation

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High fertilisation

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t2

t3

Epidemics is earlier and stronger in high fertilisation

Precigout *et al.*, 2017
Gigot et al. in prep
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Decreasing the resources for the pathogens

At the landscape scale: resource heterogeneity slows down pathogen colonization

<figure><img src="image_59.png" /><figcaption>Simulation of landscape colonisation by the leaf rust with heterogeneous fertilisation</figcaption></figure>

➤ Low fertilisation areas produce few spores and slow down pathogen dispersal in the landscape

➤ Heterogeneity in terms of fertilisation slow down landscape colonisation by the pathogen
Different mechanisms for self-regulation of pests and diseases

<table><thead><tr><th>Process</th><th>Lever</th><th>Practices and scale</th></tr></thead><tbody><tr><td colspan="3"><strong>Epidemics and attacks</strong></td></tr><tr><td>Dispersion</td><td>Density effect<br>Barrier effect</td><td>Intercropping,<br>Varieties mixture<br>Density<br>Landscape heterogeneity</td></tr><tr><td>Infection</td><td>Premunition<br>Phylloclimat</td><td>Intercropping,<br>Varieties Mixture<br>Density</td></tr><tr><td>Development of pathogens<br>(nutrition, reproduction)</td><td>Ressources<br>Predators</td><td>Crop Fertilisation,<br>Landscape Heterogeneity</td></tr><tr><td colspan="3"><strong>Plant response</strong></td></tr><tr><td>Escape, tolerance,<br>compensation</td><td>Plasticity of the<br>development</td><td>Varieties<br>Species association</td></tr><tr><td>Resistance</td><td>Plant defence</td><td>Varieties<br>Species association (push-pull)</td></tr><tr><td>Communication</td><td>Predators</td><td>Varieties<br>Species association<br>Landscape Heterogeneity</td></tr></tbody></table>

=> The potential for self-regulation of pests and diseases in agroecosystems is high.
Part III

Putting it all together: from mechanisms to
agroecosystems including both ecological functioning and
agronomic logic?
Effect of the **landscape** on pollen beetle abundance

<figure><img src="image_60.png" /><figcaption>Méligèthes
(Meligethes aeneus)</figcaption></figure>

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250m

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Relative importance of variables

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1700m

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Relative importance of variables
Complex interactions in the trophic web with unexpected effects

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- Nematodes

- Weevil

- Black Sigatoka

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⇒ Differential effect of non-Musa species richness according to the trophic behaviour of bioagressors

✓ Unfavourable to regulation for a generalists bioagressor like nematodes

✓ Favourable to regulation for a specialist like weevil

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Trade-off between yield and pest regulation

=> The pest regulation effect is necessary to compensate the competition effect of plant mixture

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Root pest regulation rate

<figure><img src="image_70.png" /><figcaption>(B)</figcaption></figure>

Global incident radiation

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Yield in kg plant⁻¹ year⁻¹

Leaf pest regulation rate

Poeydebat *et al* 2017
Conclusion

Take-home messages
Conclusion

⇒ Agroecology and biodiversity offer new avenues for pests and diseases regulation !!

⇒ What if agroecology is supposed to largely disseminate... and themself become a global change? A transition to **a new equilibrium** with a lot of unknowns
⇒ **more or less** pests and diseases? Bioagressors will adapt!!
⇒ **this may or not lead to** yield decrease
⇒ ...but counterbalanced by reduced inputs and environmental benefits.

⇒ Agroecosystems will be **more resilient** (self-regulation) **this means** with less human control : higher risk

⇒ Agroecology purpose not only concerns pest and diseases but also resilience to climate change and autonomy versus synthetic inputs (pesticides AND fertilizers)

⇒ Scientific approaches on the behaviour of these complex agroecosystems are to be reinforced in order to elucidate them
⇒ in strong interaction with farmers conceiving these systems on their farms
Thank you for your attention!

<figure><img src="image_72.png" /><figcaption>Faba-oilsee rape - Yvelines, France</figcaption></figure>

<figure><img src="image_73.png" /><figcaption>er, Réussir Fruits & Légumes</figcaption></figure>

<figure><img src="image_74.png" /><figcaption>© A. Jullien</figcaption></figure>

Agroforestry, Toulouse area, France

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