Archivio Journal of Plant Pathology

Abstract:

Peppermint (Mentha piperita), a herbaceous plant in the family Lamiaceae, is a medicinal herb widely grown in Iran. Symptoms of leaf spot were observed during a survey in peppermint fields of Kerman (southeast Iran) in November 2012. In some fields, more than 40% of the plants showed leaf spots. Samples of infected leaves were surface-sterilized with 0.5% sodium hypochlorite, rinsed with sterile distilled water, cultured onto potato dextrose agar (PDA) and incubated at 25°C. After seven days, dark olivaceous colonies developed which produced profuse golden brown, branched, and septate hyphae, and muriform conidia in long chains on straight and septate conidiophores. Based on the morphological characters, the fungus was identified as Alternaria alternata (Simmons, 2007). To confirm identification, DNA was extracted from a single spore isolate. The internal spacer (ITS) region was amplified using the universal primers ITS1 and ITS4 and sequenced. The resulting sequence (560 bp), which showed more than 99% identity with A. alternata isolates in BLASTn analysis, was submitted to GenBank (accession No. KM076936). Pathogenicity tests were performed by spraying suspensions of 104 spores per ml on the leaves of healthy peppermint plants. After 10 days, an average of 47.85% of the leaves of inoculated plants showed spots similar to those observed in the field. A. alternata has previously been reported as a leaf spot pathogen on peppermint from Poland (Zimowska, 2007) but, to our knowledge, this is its first report on peppermint in Iran.