Résumé
Coffee is one of the world's largest traded commodities. In particular, coffee represents one the key export and cash crops in tropical and subtropical developing countries with generally a favourable impact on the social and physical environment. However, root-knot nematodes (Meloidogyne spp.) have become a major threat in all-major coffee growing (Coffea arabica L.) and constitute the major agronomic constraint in most Latin American countries. By a multidisciplinary approach and the development of several breeding tools, the present project aims at improving the resistance to root-knot nematodes of coffee varieties grown in Latin America. The selected strategy for developing genetic durable resistance relies upon the combined development of i) varieties (either cultivar or rootstock) associating complementary well-characterised resistance genes, and ii) optimised variety-deployment strategies based on a careful characterisation of root-knot nematodes populations damaging coffee trees. In 2002, the main achievements included: - Surveys of Meloidogyne populations damaging coffee roots were performed in Brazil and Central American countries. Most of the species were identified and a diversity analysis has been undertaken. - Plant material was prepared and a collection of nematode isolates was established as initial steps for the determination of the spectrum of resistance conferred by the available root-knot nematode resistance-genes. Preliminary study in relation with the resistance to M. exigua originating from C. canephora showed a homogenous behaviour among M. exigua populations. - The histological analysis of infected susceptible roots according to the time course of infection confirmed that M. exigua induced the differentiation of large feeding site. The development of the nematode in roots led to the production of eggs, indicating the high level of susceptibility of this coffee genotype. - Molecular markers tightly linked with the resistance to M. exigua were identified. A largeinsert DNA library of C. arabica was constructed for further molecular work. Additional microsatellites markers were developed. - Field trials were established in order to compare different rootstock types for their adaptation to various agro-ecological conditions and resistance to root-knot nematodes. (Résumé d'auteur)