Colletotrichum species associated with anthracnose of cashew tree

Abstract

Anthracnose caused by members of the Colletotrichum gloeosporioides species complex is an important disease in cashew nut producing countries worldwide. In this study, we investigated the phylogenetic definition of a set of 61 Colletotrichum isolates associated with the cashew tree, belonging to this species complex. Single spore isolates were obtained from symptomatic cashew leaves collected in Brazil and Mozambique. Phylogenetic analyses were performed through Bayesian Inference and Neighbor-Joining based on ApMAT dataset. BI was carried out using concatenated partial sequences of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT) and ITS-5.8S rDNA. The ApMat-based phylogeny provided the best resolution in the delimitation of six lineages, namely, C. siamense sensu lato, C. asianum, C. tropicale, C. fructicola, C. theobromicola, and a still undesignated Colletotrichum sp., potentially a novel species. Morphological characters of the taxa in the species complex could not clearly separate species within the complex. Selected isolates of all identified species were pathogenic, triggering typical symptoms of cashew anthracnose on leaves when tested for pathogenicity toward cashew seedlings. Yet, two taxa (C. siamense sensu lato and the still undesignated taxon) are considered to be dominant groups of species because were the majority in number and were represented by both isolates from Brazil and Mozambique. All known species found in this study are reported to have worldwide geographic distribution. These findings show that cashew anthracnose is caused by at least six different species, five of them known from other tropical trees and different regions of the world in association with plant diseases in various agriculturally important crops. Colletotrichum gloeosporioides stricto sensu was not found causing cashew anthracnose.