Pestalotiopsis microspora causes leaf spot on Adenium obesum

Abstract

Among the main ornamental plants grown in Brazil, Adenium obesum stands out for its appearance, drought resistance and beautiful flowers. However, diseases can be a limiting factor because they affect crop quality and yield. The aim of this study was to report the first occurrence of Pestalotiopsis microspora as the causal agent of leaf spots on desert rose. A. obesum leaves with necrotic spots on the edges and/or tips were collected for indirect isolation of the pathogen. Three morphologically similar fungal isolates were obtained. In pathogenicity testing, healthy leaves were inoculated with mycelial disks and controls with disks containing potato dextrose agar (PDA) medium. Symptom development was assessed on a daily basis, followed by reisolation. The DNA of pure cultures was extracted and submitted to PCR using the primers ITS1 and ITS4. The PCR product was sequenced. The inoculated leaves initially developed symptoms of chlorosis that progressed to necrosis. The fungal colonies exhibited white mycelia with radial, cottony growth and the formation of dark masses of conidia and hyaline, branched septate hyphae. The euseptate conidia had two hyaline cells (apical and basal) and three dark-coloured fusiform median cells. The morphological characteristics of the isolates were similar to those described for the genus Pestalotiopsis. When compared to sequences deposited in GenBank, the sequences of the ITS gene showed 100% identity with the Pestalotiopsis microspora species. These results extend the range of known hosts of this pathogen, since this is the first report of P. microspora attack in Adenium obesum.