First report of Alternaria leaf spot on gerbera (Gerbera jamesonii L.) in north of Iran.
Gerbara is a genus of ornamental plants from the sunflower Asteracea family with great commercial value which grown in several areas of the world. Alternaria leaf spots of gerbera (Gerbera jamesonii L.) were observed on plants from different greenhouses in north of Iran. The sypmtoms at the initial stage of the infection were brown, small, scattered spots on the leaves that gradually become round or irregular. Spots coalesce to affect large areas of leaves and cause defoliation. Affected plants showed lower vitality, suppressed development and fewer, smaller, distorted in shape flowers. Fungi isolates, obtained from infected leaf tissues were grown in pure culture and on the base of morphological characteristics of colony and conidia, the pathogen was identified as Alternaria alternata. The fungus produced effuse, olivaceous black colonies with dark olivegreen margins, and abundant branched septate, golden brown mycelium. The conidiophores were branched, straight, pale brown to olive brown. The pale brown conidia of the isolates were catenated in long, sometimes branched chains of 5-12 spores. The size of conidia varied from 20-63 µm in length and 9-18 µm in width and usually ovoid to ellipsoid or obclavate with short conical beak at the tip. Conidia had two to three transverse septa and usually several longitudinal septa. Pathogenicity tests conducted on healthy potted gerbera plants in a glasshouse showed typical leaf spot symptoms after two weeks. This is the first report of a leaf spot disease of gerbera in north of Iran.