Résumé
Corynespora cassiicola is a necrotrophic ascomycete fungus affecting a wide range of plants. In rubber tree, C. cassiicola causes the Corynespora Leaf Fall (CLF) disease, responsible for sporadic but often severe epidemics in rubber plantations in most Asian and African producing countries. Divergence in the susceptibility of rubber clones to CLFD in various locations revealed the existence of different physiological races. A toxin secreted by the fungus (cassiicolin) has been identified as the primary determinant of C. cassiicola pathogenicity. An optimized purification protocol allowed the preparation of highly purified toxin in sufficient amount to fulfil its molecular characterization. Cassiicolin was shown to be a 27 amino acids glycosylated protein with 3 disulfide bounds. To test whether qualitative differences in the toxin may influence the pathogenicity, four strains of various geographic origins and with different virulence profiles were analysed comparatively. Biochemical purification of the toxin followed by mass spectrometry was attempted from all four strains, as well as cloning and expression analysis of the full cassiicolin-encoding gene, when detected. The results are discussed with respect to the pathogenicity of the selected strains.