Assessment of the role of age and light availability in leaf mortality in mango tree.[OS 6-1]

The branch autonomy principle states that the branch carbohydrate economy can be largely independent of the other branches of a tree. This may influence fruit growth and affect global crop yield. While this concept has already been tested on different fruit tree species, branch autonomy has not been characterized with respect to fruit growth in the mango tree. The mango tree, a major fruit production in tropical and subtropical regions, exhibits phenological asynchronisms indicating decorrelated development of branches within a tree and thus a possible autonomy among them. To assess this autonomy, we used a quantitative model of the vegetative and reproductive development of mango tree architecture and fruit quality. This functional-structural plant model combines complementary architectural, phenological and ecophysiological knowledges and relies on two sub-models parameterized for the cultivar Cogshall in Réunion Island. The first sub-model simulates stochastically the development of mango tree architecture, growth units and inflorescences, based on empirical rules. A recent improvement was to take into account leaf mortality to achieve more realistic foliage distribution. Fruit growth and quality development are simulated by a second sub-model that simulates carbon- and water-related processes occurring at the fruiting branch scale during the fruit-growing season. This model assumes the independence of the fruiting branches in terms of carbohydrates synthesis and allocation. We conducted a sensitivity analysis on the size of the fruiting branches and compared the simulated and measured fruit fresh masses at maturity in order to assess the level of autonomy of the branches regarding carbohydrates supply for fruit production. Our results show that the leaf to fruit ratio and the simulated fruit fresh mass increase proportionally with the size of the branches. The comparison with measured fruit masses indicates that a branch size of 2 to 3 GUs are sufficient with respect to fruit growth

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. (Résumé d'auteur

Impact of some crop management practices on tomato infestation/infection by the whitefly-begomovirus complex in Cuba

Introduction. In the framework of the INCO-BETOCARIB Project titled "Begomovirus disease management for sustainable production of tomato in the Caribbean" which operated from 2003- 2006, we conducted a survey aiming at assessing the impact of cultural practices on the infestation/infection of tomato plots by whitefly (Bemisia tabaci)/begomovirus (TYLCV). Materials & Methods. The survey was conducted in the West and Central regions of Cuba in respectively 100 and 96 tomato plots in open fields (71% of the plots) and under shelter (29%). Results and Conclusion. Analysis of data showed that both TYLC resistant (e.g. Vyta and ARO 8479F1) and susceptible (e.g. Amalia and HC 3880) cultivars were cultivated in open fields whereas only resistant cultivars were cultivated in sheltered plots. In open fields, TYLC disease incidence and severity were found to be significantly higher on susceptible, compared to resistant cultivars. Whitefly infestation and TYLCV incidence were higher in the West region as compared to the Central region, while the reverse was observed for severity of the disease. Whitefly infestation in open fields was high when no chemical protection measure was applied in the nursery and low under high chemical protection. The reverse tended to be observed when considering chemical application in the field, which might be an indirect indication that chemical protection negatively affects natural regulation processes. Implications of the results of this survey for agroecological management of the vector/disease complex in Cuba are discussed. (Résumé d'auteur