Archivio Journal of Plant Pathology

Abstract:

Oleander (Nerium oleander) is an evergreen ornamental extensively grown in Iran. In April 2013, dark brown to black leaf spots were observed on oleander leaves in the Yazd province. As disease progressed, leaf spots increased from 10 to 20 mm in diameter and changed from circular to elliptical in shape. Three leaf spots were excised, surface-sterilized in 0.5% sodium hypochlorite and placed on potato dextrose agar (PDA). Colonies were initially white, then turned from orange-yellow to medium red with abundant aerial mycelium. Macroconidia were rare and scattered (mean of 20 spores: 25.92×4.43 μm) with three to four septa; microconidia were slightly curved, ovoid, and fusiform (mean of 20 spores: 11.05×3.97 μm) with zero to two septa. Spherical chlamydospores (mean of 20 spores: 11.01 μm) were terminal and intercalary, single or in chains. Based on these characteristics, the fungus was identified as Fusarium brachygibbosum Padwick (Al-Sadi et al., 2012). Pathogenicity of the fungal isolate was proven by placing seven-day-old mycelial plugs (5 mm) grown on PDA on oleander leaves. Eight days after inoculation, leaf spots developed on the inoculated plants from which F. brachygibbosum was re-isolated. Identification of the fungus was confirmed by comparing the sequences generated from the internal transcribed spacer (ITS) region of the ribosomal DNA (ITS4 and ITS5 primers) (White et al., 1990). These sequences shared 100% nucleotide similarity with those of F. brachygibbosum (GenBank accession No. KF985966). This pathogen has previously been reported on date palm (Padwick, 1945) and as the causal agent of dieback on Euphorbia larica (Al-Mahmooli et al., 2013). To our knowledge, this is the first report of F. brachygibbosum on oleander.