An ecologically intensive approach for the design of sustainable horticultural systems in the tropics
Fruit and vegetable growers in the tropics are faced with crop protection issues resulting in food insecurity and low-income in low-input traditional agro-systems. In intensive systems, pesticide-induced adverse impacts on human health and the environment may occur. Setting up an "ecologically intensive" horticulture by modifying agro-systems to mobilize natural regulation mechanisms taking ecological processes as a source of inspiration, has become a major challenge. This implies a shift from a "tactical" approach based on preventive and curative chemical treatments (agro-chemistry) to a "strategic" approach based on preventive and natural methods (agro-ecology) for the regulation of pests/pathogens infestations/infections. Horticultural cropping systems provide ideal frameworks for studying the effects of the planned introduction and management of plant species diversity (PSD), on pest and disease impact. The Cirad Omega3 Project builds on case studies representing a broad range of PSD levels, scales and deployment modalities, according to an a priori typology of pests and diseases based on their life-history traits. Obtained and anticipated outcomes of these studies concern both i) knowledge on ecological pest and disease regulation processes that can be mobilized in horticultural systems, ii) tools and methods for incepting and evaluating innovating pest and disease-resilient cropping systems. We present here the global approach and first results obtained within this framework regarding i) introduction of service plants with sanitizing/ allelopathic effect managed as green manure for reducing tomato bacterial wilt caused by Ralstonia solanacearum, ii) potential of trap crops/barriers for reducing infestation and damage of tomato fruit worms Helicoverpa armigera on okra in Niger and Helicoverpa zea on tomato in Martinique. Results of these case studies on non-specific disease and pests with respectively low and high dispersal ability, provide decision rules which help set up models to predict the impact of PSD deployment modes on the studied bio-aggressors or other pathogens/pests with similar life-history traits.