Phenotypic and Molecular Characterizations of Strains of Lasiodiplodia theobromae (Pat.) Griffon & Maulk, Pathogen Associated with Black Rot Cocoa Pods in the Tshopo Province, Kisangani Region (DR Congo)

Abstract

The cocoa tree (Theobroma cacao L) is a persistent perennial crop in tropical regions whose production period is sufficiently spread out over the whole year.  As a result, it offers pathogens conditions for survival without real disruption of their life cycle.  Symptoms of cocoa pod black rot disease have been observed in both the Bengamisa cocoa growing area and the Yangambi area in the Democratic Republic of Congo (DRC). This study aimed to characterize the strains of Lasiodiplodia theobromae on cocoa trees in the Kisangani region.  Macroscopic and microscopic observations were made on the pods while the identification of the species was confirmed by a molecular approach based on the sequencing of part of the ribosomal DNA including the ITS regions (internal transcribed spacers) and the 5.8S gene.  The results of this study showed that the phenotypic characteristics of the strains isolated in the two cocoa growing areas were typical of the L. Theobromae species. These are in particular the spots of soft rot, initially brown, gradually evolving into soot-black which subsequently produced a sort of whitish powder on the surface of the diseased pod.  However, the fruiting of the fungus in the PDA medium gave rise to the latter's mycelia, initially whitish, which darkened as they matured.  In addition, PCR amplification followed by sequencing of the fungal strain was beneficial by removing any doubt about the nature of the fungal species isolated in the two cocoa-growing areas.