Modelling nematode populations in horticultural systems

To date, nematode dynamic models have been very simple, driven only by few parameters without accounting for host quality or environment characteristics. However, these approaches provided only a basic description of'nematode population dynamics, and a few mechanistic insights into the relation between the nematode, host and the environment. Recently, more specific models were developed for a wide range ofplant-parasitic nematodes and horticultural systems (Pratylenchus penetrans in rotations; potato cyst nematode and Meloidogyne incognita on potato systems; Radopholus similis, Pratylenchus coffeae and Helicotylenchus multicinctus on banana based systems). These models are either based on biological processes (population growth, initial or maximal population) or statistical approaches; often with dynamic outputs. These models account fqr the specificities of the relation in the nematode-plant complex, e.g. through the root biomass fluctuation which represents the food resource for nematodes. After reviewing the existing models that simulates nematode dynamics in hOliicultural systems, we present the example of the SIMBA-NEM model dedicated to plant-parasitic nematodes in banana based systems. We highlight the way this modelling approach allows integration of existing knowledge and permits us to re-examine research about nematode-plant relationship. We emphasize how these models may help to optimize the effect ofnematicide applications and participate to the design of sustainable and more environmental-friendly cropping systems. We also focus on the use of models to tackle issues surrounding new banana varieties. Finally, we discuss the relevance of the modelling scale from the root to the field, and its implication in the efficiency in forecasting population dynamics and plant damages. We examine the .needs for spatially explicit models that take into consideration the spatial variability of soil moisture or the availability of host root biomass. (Texte intégral

Sintra-root system heterogeneity of Radopholus similis population dynamics on bananas, a modelling approach

At the plant scale, the heterogeneity of pest populations have long time been ignored. Concerning plant-parasitic nematodes, there is strong evidence that these populations could be highly heterogeneous in space, mostly due to their low dispersal capacities. On bananas, this heterogeneity is even emphasized by the semi-perennial nature of this plant and by the recurrent development of a new emerging root system at every crop cycle. Hence, the root biomass resource for plant-parasitic nematodes is not available constantly either in terms of quality or quantity but accordingly to the phenology of successive suckers. We adapted the SIMBA-NEM model to simulate nematode sub-populations for each sucker, at the scale of the banana mat. SIMBA-NEM was primarily designed to simulate the plant-parasitic nematodes of banana at field scale, considering the global population of the simulated plot, the model used two population parameters, 'r' the growth rate of the population and 'K' the carrying capacity of root resource. The simulation of the root biomass of each sucker was performed with the SIMBA-GROW module. We introduced a new parameter related to the rate of infestation from one sucker to the successive ones. We confronted the simulations performed for the burrowing nematode Radopholus similis over four cropping cycles with field measures of R. similis populations, separately acquired from each suckers' root system. We conclude that the model reproduce correctly the pattern of population dynamics for the successive suckers. Our results highlight the importance of the banana vegetative development on the population dynamics of R. similis. This improved model should be a useful tool to design new management strategies of banana nematodes, especially when it deals with cultural practices performed at the plant or the organ levels, e.g. desuckering techniques or pesticide applications. Finally, this work provides evidence that nematode populations might be managed to a more local scale and that speed development of plant organs is of importance on their population dynamics. (Texte intégral

New insights on nematode management on bananas in the french Caribbean

Given the increasing societal demand for more eco-aware farming practices during the last decade, considerable changes and innovations have already occurred in banana cropping systems worldwide, from the former concept of Integrated Pest Management (IPM) that relied heavily on the use of chemical control towards a more sustainable concept of Integrated Crop Management that favours non-chemical pest management. These innovative methodologies were particularly more rapidly adopted in countries where environment, health and safety conditions were politically prioritized. But there are also additional causes to this rapid transformation for designing more sustainable cropping systems, i.e. economical endowments, environmental policies, and retailing chain requirements. In the French West Indies, the reduction of pesticide impact on air, soil and water quality is a major goal of agronomy research. As a result, management approaches that combine different tools for pest management such as use of improved fallows, crop rotations, replants with banana vitroplants, resistant cultivars are discussed in relation with the different banana cropping systems. As an example, alternate cropping of bananas, pineapple or sugarcane combined with appropriate horticultural practices (chemical destruction of former banana plants, weeding during fallow) have already eradicated the burrowing nematode Radopholus similis from some areas in Martinique. In addition, some forage crops (Brachiaria spp.) or leguminous cover crops (e.g. Crotalaria spp., Neonotonia wightii) may be used in intercrop to remove or decrease under threshold level some other key-pests (e.g. lesion nematodes Pratylenchus coffeae, spiral nematodes Helicotylenchus multicinctus and root-knot nematodes Meloidogyne spp.) from soil. However, the adoption of these innovative practices strongly depends on the farming contexts and an evaluation of these innovations using crop models might be useful tools to help researchers and stakeholders. (Texte intégral

Early assessment of pest dynamics on new crop varieties : A modelling approach applied to banana-nematode systems

Breeders develop an increasing number of new crop varieties with potentially interesting characteristics in regards to their resistance or tolerance to pests. Nevertheless, the long-term assessment often requires heavy multi-local in-field measurements. Furthermore, the interactions between two or more pest many limit the relevance of field results on the long-term. Here, we present a methodology that use cropping system model to evaluate both the long-term evolution of the pest dynamics and the overall sustainability of the cropping systems based on include new varieties. We illustrate our method with the case of the new synthetic banana hybrid FB920 (Musa spp., AM group) - plant-parasitic nematodes complex. FB920 was designed to be resistant to the Sigatoka Disease and Black Leaf Streak Disease, caused respectively by Mycosphaerella musicola and Mycosphaerella fijiensis. Herein, we used the SIMBA model (a model to simulate phenology, growth, and plant-parasitic nematode/banana interactions) to examine the population dynamics of plant-parasitic nematodes in cropping systems with this new synthetic hybrid FB920 in various initial conditions. We used short term experiments to calibrate the SIMBA model to account for the growth and the development of the FB920 variety and to simulate the dynamics of the burrowing nematode (Radopholus similis) and the spiral nematode (Helicotylenchus multicinctus). Results from simulations show that in the long term the spiral nematode populations can overtake the burrowing nematode populations and that nematodes populations are smaller than in Cavendish banana fields. (Texte intégral

Model based evaluation of cover crops for banana cropping systems

There is actually a surge for reintroducing biodiversity in agricultural systems in order to reduce chemical inputs, suppress pests, and close biogeochemical cycles. The use of cover-crops is a promising way to reintroduce biodiversity into the fields. Cover-crops have the potential to decrease chemical use against weeds (by competition) and pests (by increasing in natural enemies). To decrease herbicide use, suitable plants must be able to grow in appropriate conditions, to do not compete the cultivated crop for nutrients or water, but should compete weeds for light and space. There is a trade-off between these objectives. Banana is a semi-perennial crop, each plant develops at its own rhythm leading to an unsynchronized plant population in three years; canopy and nitrogen demand of the crop follow this unsynchronized pattern. Banana cropping systems remain based on bare soil management and a large amount of herbicides is used. In tropical environment, the growth of weeds and cover-crop is complex because it is not constrained by seasons; a constant growth is possible due to relatively constant climate. In these conditions, variation in radiation due to canopy closure is one of the major drivers of their growth. We developed a model based method to assess the suitability of cover crop for a given cropping system context. This method first relies on early measurements of cover crop performed on the field. Then, we used a simulation model to contextualize the growth of cover crops and to assess their capacity to control weeds, to compete the cultivated plant, and to sustain on the long term under the shade of the main crop. This approach allows an early selection of cover crops that should be tested in real intercropping in the field. We present results of this evaluation for 11 species intended to banana intercropping. (Texte intégral

Management of banana nitrogen fertilization : taking into account nitrogen from organic origin

Les règles de fertilisation azotée en bananeraie prennent rarement en compte l'azote fourni par la minéralisation de la matière organique du sol ou des résidus de culture. Les résultats d'une expérimentation comparant différentes doses d'azote montrent qu'à partir d'un niveau de fertilisation azotée inférieure aux recommandations établies sur la base des prélèvements par la culture il n'y a plus d'augmentation du rendement. Ceci suggère que l'azote des engrais n'est pas la seule source d'azote pour le bananier et l'existence d'une offre d'azote non prise en compte dans la fertilisation conventionnelle. La matière organique du sol fourni des quantités d'azote minéral très variables en fonction du type de sol. Dans les andosols d'altitude des Antilles, les quantités d'azote issues de la minéralisation de la matière organique du sol couvrent une partie importante des besoins du bananier. L'utilisation d'un modèle simulant la dynamique des restitutions organiques et de l'absorption d'azote par le bananier (SIMBA) permet de définir des stratégies de fertilisation garantissant la satisfaction des besoins du bananier tout en limitant les pertes d'azote par lessivage. (Résumé d'auteur