Morphological and Molecular Identification of the Pathogen Associated with Pink Disease of Cocoa (Theobroma cacao L.) in the Nawa Region of Côte d'Ivoire

Abstract

Pink cocoa disease, long considered a minor disease in ivorian cocoa farming, has become a major problem for cocoa production, especially in the Nawa region (Soubre), one of the main cocoa-producing areas in Côte d'Ivoire. The disease is characterized by the appearance of spots on infected branches, with fruiting bodies color white to salmon, and red to brownish lesion under the bark of the attacked trunk or branch. When attacks are severe, they cause cankers, leading to defoliation and death of the tree. In Côte d'Ivoire, no studies have yet been carried out on this disease. This study was therefore carried out in this region in order to identify the pathogen. Thirteen (13) farms in three localities of the region were surveyed, and 03 samples of infected organs were collected from each infected plot. Nine isolates were characterized on the basis of morphological characteristics (mycelial growth, color and size of conidia) and molecular characteristics (PCR-sequencing tests) using universal primers (ITS1 and ITS4). The results revealed morphotypes characterized by striated, radiated, sparse or cottony facies, with an average growth rate of 10.70 ± 3.20 mm/d. Alignment of the ITS rDNA sequences of these isolates against Erythricium salmonicolor sequences available in GenBank identified them as Erythricium salmonicolor, with a similarity rate ranging from 92 to 100%. In addition, phylogenetic analysis of E. salmonicolor strains revealed low genetic diversity. This study therefore provides a basis for further research into the pink disease of cocoa in Côte d'Ivoire.