Abstract
Human activities increasingly frequent and persistent in ecosystems on one hand, and cropping system intensification on the other hand partly with radical methods to control pests and diseases of crops, raise questions about the ecological risks related to biotop changes, including disturbances of living organism communities. Plant-parasitic nematodes (PPN), microscopic round soil-borne worms that cause significant losses of crop production, are everywhere present in communities. They respond quickly to external forces (e.g. human and environmental) by changing the structure of their communities. In this thesis, we seek to better understand the effect of the factors involved in the assemblage of PPN species in communities associated with the Mediterranean olive tree and to determine the response of these communities to forces imposed by olive domestication, by crop intensification and by various environmental factors. The study was conducted in all olive-growing regions in Morocco (traditional low density and high density orchards), in refugia areas for wild olive (oleaster) and on feral olive trees. The soil and climatic factors that characterize the sampling sites were also considered. The analysis of the nematofauna revealed a wide species diversity, many species being described for the first time on olive tree, and a new species (Meloidogyne spartelensis) have been discovered. The diversity, the species / trophic / functional structure of the communities, the dominance of the taxa, and the community patterns are strongly affected by the various forces considered. The increasing anthropogenic gradient (wild vs feral vs traditional cultivation vs high-density cultivation) is the variable that mostly impacts the diversity by reducing the species richness and increasing the abundance of PPN. A particular attention was attributed in this study to the diversity of root-knot nematodes Meloidogyne, a major pest of the olive tree. It revealed that M. javanica is widespread in orchards and olive feral, while other species (M. arenaria, M. hapla and M. spartelensis) are confined in oleaster refuge areas. In order to analyse the genetic diversity, morphological and molecular markers have revealed a significant diversity between and within different Meloidogyne populations. These thesis studies confirm that both the diversity and the structure of the PPN communities could be relevant indicators to assess soil health in agro and ecosystems, by correlating diversity and pathogenicity of communities. They therefore emphasize the importance of parasite diversity as a main variable to consider for inspiring pest control strategies based on the concept of diversity resilience (even if it concerns parasites) for sustainable management of PPN communities and for environment preservation.