Identification of Calonectria variabilis isolated from Anacardium occidentale trees exhibiting leaf blight symptoms

Abstract

Anacardium occidentale is the tree source of cashew nuts, a commodity with increased demand globally and threatened by several diseases. Here we report on the occurrence of a disease that has severely affected production of cashew nuts in Panama and that can be of regional importance. Our first observation of this disease was in 2013, in the locality of Gamboa (Colon, Panama). Blight symptoms of the disease starts with foliar lesions characterized by initial necrotic points surrounded by yellow discoloration or chlorotic zones. These lesions progressively expand, transforming into larger, brown patches with rounded to irregular shapes. Lesions can coalesce and cover entire leaves causing them to drop and produce defoliation of entire branches or trees that become unproductive. Trees with similar symptoms were later observed in several provinces in Panama indicating that the disease was widespread in the country. We obtained consistent isolation of the same fungus from lesions on A. occidentale from multiple localities and pathogenicity tests were conducted on detached leaves as well as on healthy leaves on an adult tree. Morphological and phylogenetic analyses of the isolated fungus showed that the causal agent was Calonectria variabilis, a fungus previously reported to occur on Schefflera morototoni, Theobroma grandiflora, and Eucalyptus. This is the first time that C. variabilis is reported as a pathogen of A. occidentale and the first record of this species for Panama.