A new leaf disease on Populus euphratica in south-western Iran

Abstract

During the winter of 2012, a leaf spot disease was observed on Euphrates poplar (Populus euphratica) in the forest areas of Khuzestan province, south-western Iran, causing significant damage in the Karun's riverside forests. Symptoms consisted of necrotic dark brown, circular to oval, 5- to 10-mm spots on both surfaces of the leaves. A fungus having distinct dictyospores similar to those produced by Alternaria spp. was observed. The morphological characteristics, as well as the phylogenetic analysis of the internal transcribed spacer (ITS1-5,8S-ITS2) region, confirmed the identity of the strains belonging to the species Alternaria alternata. Pathogenicity tests were conducted on the alive leaves of P. euphratica on the young branches, as well as on the detached leaves in Petri dishes, through inoculation with spore suspension. Target spot symptoms similar to those observed in naturally infected leaves were developed on the inoculated leaves seven to 10 days after inoculation in both the inoculation procedures. A. alternata was consistently re-isolated from the spots. Interestingly, similar symptoms were observed 7 days after detached leaf treatment with droplets of 15-day-old fungal culture filtrate, suggesting the production of pathotoxic compounds by the fungus. To our knowledge, this is the first report of A. alternata causing leaf spot on Euphrates poplar in Iran.