Archivio Journal of Plant Pathology

Abstract:

In October 2013 plants with necrotic leaves and cankers on the stems were observed in oregano crops (Origanum vulgare ssp. hirtum) at Tres Esquinas (Mendoza, Argentina). The necrosis had a basipetal progress, affected the center of the bush and, in some cases, resulted in the death of the plant. Following isolation on potato dextrose agar (PDA), effuse greyish to brown colonies developed, which produced irregular black sclerotia. The mycelium was branched, septate, hyaline to brown-coloured and produced conidiophores bearing one-celled, egg-shaped and hyaline conidia, grouped in glistening heads. Based on these morphological traits, the fungus was tentatively catalogued as Botrytis sp. (Ellis, 1971), until molecular identification was performed. Its pathogenicity was tested by inoculating oregano stems with agar plugs from fungal colonies, while control plants were inoculated with sterile agar plugs. The plants were covered with a plastic bag for 24 h. After 5 days, the field syndrome was reproduced in inoculated plants, which showed an incipient necrosis of the stem and wilting of the leaves. From these plants the pathogen was successfully re-isolated, fulfilling Koch’s postulates. Molecular identification was carried out by PCR amplification using the primer pair ITS1/ITS4 (White et al., 1990). The amplified product was purified, sequenced (GenBank accession No. KT921335) and compared with the equivalent sequences from database. A complete match score was found with Botrytis cinerea, confirming the identity of the pathogen. B. cinerea was recorded from Italy as a pathogen of Origanum majorana (Pensa et al., 2007). To the best of our knowledge this is the first report of B. cinerea affecting oregano crops in Argentina.