Archivio Journal of Plant Pathology

Abstract:

In 2012-14, agave (Agave americana) plants with leaf spot symptoms were observed in Mazandaran province (Iran). Initial symptoms consisted of 3-5 mm dark brown spots, circular to ovoid, enlarging to 3.5-10 cm in diameter. Large lesions often coalesced. Symptomatic leaf tissue was surface-sterilized and transferred to potato dextrose agar (PDA). The cultures gave rise to initially white colonies which turned grayish-black later due to abundant sporulation. Microscopic observations of the colonies revealed brown septate hyphae and simple or branched conidiophores 30-70×3-4.5 μm. Dark brown conidia were observed in chains of 3-7, measuring (12.2-) 20.5 (- 26.7)×(5.2-) 9.4 (-12.5) μm, ellipsoid to ovoid with 3-6 transverse and 0-3 longitudinal septa. Based on morphological characteristics, the fungus was identified as Alternaria alternata (Simmons, 2007). Artificial inoculation (on healthy leaves of A. americana at >85% RH and 25°C) resulted in development of disease symptoms from which a fungus showing the same characteristics of the inoculated strain was re-isolated. DNA was extracted and used to amplify ITS-rDNA (White et al., 1990), β-tubulin (O’Donnell and Cigelnik, 1997) and Alt α 1 regions (Hong et al., 2005), whose sequences [GenBank accession Nos. ITS (KM371730), TUB2 (KM289070) and Alt (KM289069], showed a high identity with the comparable reference sequences (ITS: 100%, TUB2: 100% and Alt: 99%). Agave leaf spot caused by A. alternata (Gautam, 2013) has previously been reported from India. To our knowledge, this is the first record of A. alternata causing leaf spot disease on agave in Iran.