Résumé
Background. Obtain sustainable varieties resistant to disease is one of the main goals of genetic improvement of cocoa. In partnership between CEPLAC (Comissão Executiva do Plano da Lavoura Cacauiero) and CIRAD (Centre International de Recherche Agronomique pour le Développement), studies to detect and characterize QTLs for resistance to witches' broom (Moniliophthora perniciosa) and to pod rot (Phytophthora .palmivora), are conducted. QTL detection for resistance to Phytophthora. palmivora, were carried out from a segregating F2 progeny (172 ind) resulting from the cross between Scavina-6 (resistant Forastero clone) and ICS1 (susceptible Trinitario clone) . Phenotic symptoms were revealed seven days after inoculation by a P. palmivora strain (CEPLAC phytopathology laboratory collection) . A drop of 0.2ml of a concentrated solution of zoospores was deposited on leaf discs. Phenotypic analyses on necrosis severity (note 0 :without penetration point until note 5 :total necrosis) were obtained from sixty discs per genotype. QTL analyses were carried out using a genetic map established with 202 markers (SNPs and SSRs). The remaining par of the F2 population (972 individuals excluding plants used for the QTL analysis), was genotyped with the SSR markers associated with QTLs detected. The 972 genotypes were classified according to the presence of favorable QTL-allele or unfavorable QTL-allele. Phenotypic analyses on necrosis severity were carried under the same conditions as for the QTL analysis and two sets of thirty seven selected genotypes with favorable QTLs and unfavorable QTLs, were inoculated. Results. The remaining par of the F2 population (972 individuals) was genotyped with the SSR markers : mTcCIR91, mTcCIR175 et mTcCIR430, respectively associated with the three QTLs detected in the linkage groups 10, 3 and 2, explaining 25% of the total variation. Statistical analysis results presented here, show a significative difference between both sets of plants, showing a very efficiency selection for Phytophthora resistance only with these markers close to QTLs. Conclusion. Scavina-6 is also an important source of resistance to witches' broom (Moniliophthora perniciosa) The same approach using this same F2 population Scavina-6 by ICS1, is underway to select resistant plants. (Résumé d'auteur)