Molecular and Morphological Characterization of Colletotrichum gloeosporioides Isolates Causing Anthracnose of Cashew (Anacardium occidentale L.) in Côte d'Ivoire

Abstract

Anthracnose is one of the main cashew diseases in all cashew-growing countries. In Côte d'Ivoire, all diagnostic studies of this disease have been limited to morphological identification of pathogens. Although rapid and less costly, this identification technique remains highly inaccurate. The aim of this study was to use both morphological and molecular techniques to confirm the identity of the pathogen and to evaluate the virulence of different isolates. Isolations were therefore made from symptomatic samples of anthracnose collected from four cashew genotypes throughout the country's growing zone. The isolates obtained were characterised based on morphology and then a rapid PCR diagnosis was performed using a pair of primers specific to the Colletotrichum gloeosporioides complex. Finally, tests to establish the pathogenicity of the isolates were carried out in a greenhouse. A total of 146 isolates of Colletotrichum were isolated from leaves, flower panicles, apples, and cashew nuts. These isolates had cylindrical conidia with a length ranging between 11.56 ± 0.23 and 12.81 ± 0.17 and a width varying between 4.07 ± 0.01 and 4.77 ± 0.07. These characteristics were statistically identical between agroecological zones. In addition, isolates had cottony dense or flat mycelium with a grey or white coloration. PCR amplification reactions produced an amplicon size of 380 bp confirming that isolates are C. gloeosporioides species. Pathogenicity tests established the pathogenic nature of C. gloeosporioides isolates and DBOUL-302 was the most virulent among the isolates tested. This highly virulent isolate can serve as a model for resistance screening in cashew breeding programmes or for finding effective fungicides against anthracnose.