FIRST REPORT OF LEAF SPOT CAUSED BY ARTHRINIUM ARUNDINIS ON ROSEMARY IN IRAN

Abstract

During a survey in 2013, symptoms of brown leaf spots on rosemary (Rosmarinus officinalis) were observed in greenhouses in Hamedan province, Iran. Small fragments of infected tissue were taken from the margins of leaves and were placed on potato dextrose agar (PDA) for 7 days under 12/12 h alternating cycle of light and dark at temperature of 25°C. Isolates on PDA medium were slow-growing, grayish white with floccose whitish aerial mycelium that covered entire PDA plates. Sporulation generally localized in some dark spots in aerial mycelium. Mycelium consisted of smooth, hyaline, branched, septate hyphae, 2 to 3 μm diameter. Conidiophores were erect, septate, smooth, hyaline to brown and very different in shape and size but about 5 μm in diameter and reduced to conidiogenous cells. Conidiogenous cells were pale brown, smooth, ampulliform, 6 to 10 μm long; the apical neck was 3 to 4 μm long, basal part 5 to 6 μm long. Conidia were 1-celled, dark brown, smooth, lemon-shaped to spherical, 5 to 7 μm in diameter, 2 to 4 μm wide with a germ slit at senescence stage. Based on morphological characteristics, the pathogen was identified as Arthrinium arundinis (Corda) Dyko & B. Sutton (Crous and Groenwald, 2013). The internal transcribed spacer regions (ITS1, ITS2 and 5.8s gene) of rDNA were amplified with the primers ITS1/ITS4 and sequenced (Crous and Groenwald, 2013). The sequence was deposited in GenBank (Accession No. KM035852) and in BLAST search showed 99% similarity with sequences belonging to A. arundinis in accordance with morphological identification. In order to confirm Koch's postulates, pathogenicity tests were done twice on fully developed plants. Rosemary leaves were sprayed with conidial suspension (105 spores/ml), while control plants were sprayed with sterile distilled water. After inoculation, rosemary plants were kept in a growth chamber at 25°C. One week after inoculation, leaf spot symptoms were observed on the inoculated leaves and A. arundinis was successfully reisolated from artificially infected plants. To our knowledge, this is the first report of leaf spot caused by A. arundinis on R. officinalis in Iran.