Molecular Identification of Phytophthora palmivora in the Cocoa Tree Orchard of Côte d’Ivoire and Assessment of the Quantitative Component of Pathogenicity

Black pod rot is one of the most widespread diseases in the species Theobroma cacao L. In Cote d’Ivoire, it causes significant yield losses, estimated at about 10 to 60% depending on the ecological zones. This study was conducted in order to identify Phytophthora spp isolates in the cocoa orchard by the analysis of their molecular features and assess their pathogenicity on cocoa tree leaf disks having different sensitivity. Thirty-six isolates of Phytophthora spp., from 06 producing regions (Divo, Soubre, Daloa, Duekoue, Abengourou and Aboisso) were taken from immature pods naturally affected by black pod rot. Methods of molecular analysis based on PCR-RFLP techniques, sequencing the ITS1 region of ribosomal DNA and artificial inoculation tests on cocoa tree leaf disks were used to identify Phytophthora isolates and assess their aggressiveness. The results obtained enabled to identify Phytophthora palmivora and showed a difference of aggressiveness between isolates of this species with average grades of foliar sensitivity ranging from 0.90 to 3.93.