An agroecological approach to alleviate the impact of nematodes in banana cropping systems

For many decades, control of plant-parasitic nematodes and in particular of the worldwide species Radopholus similis was mainly based on chemical nematicides not fully safe for the environment and human health. In order to develop more environmentally friendly control strategies, we started to develop in the French West Indies an innovative and modular approach based on integrated crop protection. The two first levels of this approach were conceived to promote prophylaxis in banana agrosystems. They were devoted to soil and plant sanitation. The third and more recent level, which is presented here, also integrates additional prophylatic measures to prevent the spread, in time or space, of parasitic nematodes. It thus includes the assessment of alternative management of nematode-infested crop residues along with use of prophylatic ditches to lessen spatial dissemination of the nematode R. similis. However, this third level of modules is above all built to strengthen our strategy through an ecological intensification of the banana agrosystems. It includes the alleviation of biological soil constraints such as plant-parasitic nematodes by the manipulation of the above-ground diversity (vegetal cover). Our current strategy is to introduce in banana agrosystems nematode-resistant cover plants as associated crops, thus achieving multispecific cropping systems that will be further evaluated to understand whether they become more diversified and less prone to parasitic nematodes. We are now testing the association of bananas with the deep-rooting perennial soybean Neonotonia wightii. This work is complemented by studies assessing the possibility of also having recourse to nemato-toxic plants such as Crotalaria spp. Finally, we assign a module of the third level to the diagnostics of the soil condition, using nematode community structure. This necessary step will help to assess the ecologial impact of (current and upcoming) cropping practices. Results from an ongoing study on the structure of nematode communities in banana agrosystems, varying by their level of anthropisation, are introduced. (Texte intégral

Challenging short and mid-term strategies to reduce pesticides in bananas

One of the most traded fruits in Europe and worldwide, dessert bananas have long been produced with a marked recourse to pesticides to control the various pathogens that threaten the crop. New ways are being developed to grow banana that rely less upon pesticides but rather upon agroecological measures and Integrated Pest Management strategies. These operational solutions are continuously refined by researchers, growers and other stakeholders fully implied in ensuring more sustainable banana cropping systems, and further assuring human food and health. This guide, the first of a series of five, starts by examining the lessons taught from an overall analysis of pesticide use in countries producing dessert banana, including representative European ones. Then, it goes through the main alternative or innovative solutions to reduce, in the short and mid- term, pesticide use in bananas. In particular these solutions are highlighted to alleviate fungicide, nematicide and insecticide use, which are the main pesticides used in dessert banana farming. Four following guides complete, or more specifically, exemplify the solutions recommended in this first guide. (Résumé d'auteur

Evolution and adaptation of Magnaporthe grisea populations in upland rice in Madagascar

In Vakinankaratra , where irrigated rice has been cultivated for several hundred years, blast damages increased heavily in the newly developed upland rice. Using epidemiological records, pathogen population genetic data, and pathogenicity test, we studied blast pathogen colonization of the new upland agrosystem. Genotyping with microsattelite markers, showed a significant differentiation between upland and irrigated isolates. Comparison of populations from 3 irrigated valleys (Antsirabe, Manandona, Mangalaza) showed the first two having no differentiation while Mangalaza showed slight differentiation with the two others. That is probably due to selection by the host since Mangalaza had more diversified varieties than the 2 first locations. There is no differentiation between the early isolates causing leaf blast and those causing neck blast In upland agrosystem, differentiation was observed in Mangalaza between 2004 and 2005, and in Andranomanelatra between 2005 and 2006 isolates. Differentiation from one season to the next could be observed during the study for upland isolates. However for each location, ie in Mangalaza, in Manandona and in Antsirabe, differentiation could not be observed between the 2004 and 2005 irrigated isolates. The 99 isolates selected from different branches of the genetic dendrogram formed two distinct groups according to their pathogenicity. The first group brings together irrigated isolates. They have narrow virulence spectrum, ie they could not attack most of the upland cultivars. Even irrigated isolates collected from geographically distant areas like Antananarivo, Lac Alaotra or Vakinankaratra exhibited narrow virulence spectrum. The second gathers upland isolates of Vakinankaratra region. They have a broader virulence spectrum than the irrigated ones. Among the upland isolates, those collected in 2001 showed narrower virulence spectrum than isolates collected in 2005 or 2006, suggesting that the virulence spectrum enlarged with time. Such increase of virulence was observed during surveys.The genotypic and pathotypic structure of populations for the blast fungus in the Vakinankaratra region of Madagascar suggests local adaptation of isolates from irrigated agrosystem to upland agrosystem. In the absence of recombination, and because of short distance migrations, selection for an increased virulence spectrum to attack upland cultivars led to differentiation between populations from the two rice agrosystems and also led to a specialized pathogen population highly virulent to the widely cultivated varieties in this new upland rice agrosystem. (Résumé d'auteur

Population modeling as aid to rodent control in the field

Forecasting the damages by voles on plant crops depends on a good forecast of vole population density. Biological work in Vendee from 1959 til 1968 has furnished the fundamentals of a population model. Further work on the relationship between breeding and climate enabled us to set up a practical forecasting model. This is applied by the Plant Protection Service, and the damage prevention system consists of a test trapping in winter, a population forecasting in early March, and, if necessary, poisoning in March-April. Generalization of the system is in progress

ANANABIO: A project to design organic pineapple cropping systems through a participative approach between research and producers

ANANABIO is a multi-partnership project (2016-2018) associating Research (CIRAD) with a technical institute (ARMEFLHOR) on Reunion Island (Indian Ocean) to design innovative practices for environmental-friendly organic pineapple cropping systems. Other partners of the project are the local administrative support to farmers (Agriculture Chamber and agricultural training school), professional organizations of farmers and independent farmers as well. Pineapple produced under the French Organic production specifications are marketed with the label'Agriculture Biologique' (AB) of the French Ministry of Agriculture. The project proposes through a participatory approach to encourage farmers to co-design cropping systems with agronomists and to evaluate their performances. As far as cultural practices are concerned, ANANABIO focuses on the destruction of old crops and mechanized planting, organic fertilizer application, the pest and weeds management, and production of disease-free planting material. These cropping systems should also follow the Agroecology concept that promotes an agriculture that respects and protects man in his environment. (Résumé d'auteur

Risks of new pests and diseases

Climate change will affect the social and environmental determinants of the health of human, animal and plant populations around the world. It will challenge the social and biological capacities of food systems to regulate the emergence of pests and pathogens. Especially in Low-Income (LI) and Lower Middle-Income (LMI) countries, food systems will be dealing with new pests, diseases and emerging pathogens (viruses, bacteria, mycoplasma and fungi) severely threatening the health of vulnerable people and potentially exacerbating social and economic inequalities

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