First report of Stemphylium leaf blight of garlic (Allium sativum) caused byStemphylium vesicariumin Turkey

Abstract

During a routine survey for garlic (Allium sativum) diseases conducted in late spring of 2011 in Taskopru District, Kastamonu Province in Turkey, symptoms of a new disease were observed in many locations. Initial symptoms were white flecks that enlarged and produced sunken purple lesions sometimes surrounded by a yellow to pale brown border (Fig. 1). A Stemphylium sp. was isolated from lesions on leaves showing symptoms. Based on morphological characteristics, the species was further identified as Stemphylium vesicarium (Wall.) Simmons (Ellis, 1971). Colonies were effuse, olivaceous brown to black, somewhat velvety (Fig. 2), conidia pale to mid-brown or olivaceous brown, verrucose, with up to six transverse and several longitudinal septa, mostly constricted at the major transverse septa, 20-50 x 15-26 µm (Fig. 3). For the pathogenicity test, inoculum for agar plugs was prepared from six-day-old cultures grown at 25°C on potato sucrose agar medium (PSA). PSA plugs (6-mm diameter) with fungal inoculum taken from these cultures were placed singly onto 20 intact garlic leaves, with the mycelial surface in contact with the leaf. The inoculated garlic plants were kept in pots at 25°C with a 12 hour photoperiod and 90% RH in a controlled environment chamber. After two days incubation, the fungal plugs were removed, and pots of garlic were transferred to the glasshouse with a 12 hour photoperiod at 25°C. Disease was assessed every day for up to 14 days (Zheng et al., 2009). The causal agent was re-isolated and Koch’s postulates were fulfilled. This is the first report of S. vesicarium on garlic in Turkey. Similar purple spot symptoms caused by S. vesicarium have been described on garlic in India, South Africa, Spain and Australia (Rao & Pavgi, 1975; Aveling & Naude, 1992; Basallote et al., 1993; Suheri & Price, 2000). Further studies are needed to determine the distribution and to assess the economic impact of this disease in Turkey.