Horticultural Systems in the Tropics Horticultural Systems in the Tropics Horticultural Systems in the Tropics Horticultural Systems in the Tropics

An Ecologically Intensive Approach An Ecologically Intensive Approach An Ecologically Intensive Approach An Ecologically Intensive Approach for the Design of Sustainable

for the Design of Sustainable for the Design of Sustainable for the Design of Sustainable

Horticultural Systems in the Tropics Horticultural Systems in the Tropics Horticultural Systems in the Tropics Horticultural Systems in the Tropics

A. Ratnadass , P. Deberdt, P. Fernandes, I. Grechi, B. Rhino,

P. Ryckewaert & E. Malézieux UR HortSys, Centre de coopération internationale en recherche agronomique pour le développement, F-34398 Montpellier, France

28th International Horticultural Congress, Lisbon-Portugal, 22-27 August 2010

Vegetational diversification

Resource concentration

/dilution

Enhancement of diversity

& activity of soil biota

Reduced impact of pests & diseases

Physiological resistance to pests & diseases Soil suppressiveness

Conservation of natural enemies

Barrier &

architectural effects Cycle rupture Pest deterrency

or repellency

Allelopathy

Change in microclimate Trap cropping

The planned introduction and management of plant species diversity (PSD) is the most promising way of breaking with

“agrochemistry” and moving to “agroecology” [1].

The Cirad Omega

project [3] builds on case studies taken in tropical cropping systems, representing a broad range of PSD levels, scales and deployment modalities, according to a typology of pests and pathogens based on life-history traits the most amenable to manipulation by PSD.

In Niger, in terms of trap cropping potential for Tomato Fruitworm (TFW) on okra:

Pigeon Pea > Sorghum > Cotton > Sweet corn

Low (Generalists)

Bio-Aggresseurdispersal ability

High (Specialists) Low

High

Bio-Aggressor specificity Leaf rust

/Coffee

Berry borer /Coffee

Black pod rot /Cocoa

Mirid bugs /Cocoa

Fruit flies /Cucurbit

vegetables Fruit worm /Tomato

& Okra

Bacterial wilt /Tomato

White fly /Tomato &

Okra

Landscape Field

Soil PSD deployment scale

White grubs

& Striga /Upland rice

In Martinique, in terms of Sweet corn cultivar attractiveness for TFW on tomato and « dead-end » potential:

Sugar > Java > Challenger

In Martinique, 6 plant species/cultivars were selected based on host status, potential for Multiplying Ralstonia solanacearum populations in the rhizospheric soil, anti-microbial effect and agronomic performance:

•Allium fistulosum

•Tagetes patula

•Raphanus sativus

•Mucuna deeringiana

•Crotalaria juncea cv-IAC1

•Crotalaria spectabilis

Horticultural cropping systems, which are basically multispecies-based, provide ideal frameworks for studying the impact of PSD on pest and disease impact reduction, and contribute to Omega3 via 3 case studies.

Agrochemistry

Human & environmental health

Soil fertility

Quantity of farm production Pest & disease impact

Chemical pesticide

& fertilizer application

Natural enemies Agroecology

Vegetational diversification

Quality of farm production

Sustainability of farm production Soil biological activity

References: [1] Deguine et al., 2008. Protection des cultures: De l’agrochimie à l’agroécologie. Versailles, France: Quae; [2] Malézieux et al., 2009. Agron. Sustain. Dev. 29, 43-62; [3] Ratnadass, A., et al. 2008.

Proc.Endure International Conference: Diversifying crop protection, 12-15 Oct 2008, Grande-Motte, France.

Besides agronomic benefits [2], introducing PSD in agrosystems induces different pest and disease regulation processes.

After formalizing the ecological processes studied, results on case studies on generalist vs specific pests & pathogens with low vs high dispersal ability, will provide decision-making rules which will help set up mechanistic models to predict the impact of PSD plants & deployment modes on pests & pathogens with similar life-history traits. Existing models can also be used with adequate parameterization: e.g. individual-based models for the push-pull effects on TFW at the field/immediate neighboring levels, and differential equation-based models for allelopathic effects on Ralstonia at the soil/field level.

Experimental checking of suspected PSD effects

Parameterization of existing models

Construction of mechanistic models

Model validation through observation

and experiments Hypotheses regarding PSD

effects on pests & diseases generated by observation

Ideotypes of PSD-based cropping systems resilient

to pests & diseases Adding to the

knowledge base

Indicators

Scenarios &

decision- making rules

Experimental checking of suspected PSD effects

Parameterization of existing models

Construction of mechanistic models

Model validation through observation

and experiments Hypotheses regarding PSD

effects on pests & diseases generated by observation

Ideotypes of PSD-based cropping systems resilient

to pests & diseases Adding to the

knowledge base

Indicators

Scenarios &

decision- making rules

Fruit and vegetable growers in the tropics are faced with plant protection issues resulting in food insecurity and low-income in

low-input traditional agrosystems (e.g. in the Sudano-Sahelian zone of Africa), and pesticide-induced adverse impacts on

human health and the environment in intensive systems (e.g. in French overseas islands). Setting up an “ecologically

intensive” horticulture by modifying agrosystems to mobilize natural regulation mechanisms according to the scientific

principles of agroecology, has therefore become a major challenge.