First Report of Stemphylium lycopersici Causing Gray Leaf Spot on Eggplant in China

During the June to August growing seasons in 2015 and 2016, unusual symptoms of a disease were seen on the foliage of eggplant (Solanum melongena) grown in a greenhouse in the suburbs of Harbin, Heilongjiang Province, China. More than 90% of plants in this greenhouse (45°44′20.61″ N, 126°43′34.46″ E) were affected by the disease. Symptoms in the early stages appeared on leaves, petioles, and stems as brownish-black specks, which later expanded to necrotic lesions 1 to 8 mm in diameter with gray centers and dark brown borders. As disease progressed, affected areas became chlorotic, the centers of lesions became perforated, then died, and dropped. Small pieces of infected leaves were surface-sterilized in 75% ethanol for 5 s and then in 0.1% mercuric chloride solution for 60 s, rinsed twice with sterilized distilled water, and plated on potato dextrose agar (PDA) in Petri dishes. The isolated pathogen was incubated at 28°C for 5 to 10 days with a 12-h photoperiod. A single conidia was aseptically transferred to a new PDA plate to get a pure culture of the pathogen. Conidia of the fungus were oblong with a conical end at the apex, bluntly rounded at the base, each measuring 20.8 to 51.6 μm long and 7.5 to 24.5 μm wide, and constricted at 3 to 5 transverse septa. Conidiophore were pale to medium brown, mostly 145 to 165 × 6.5 to 7.5 μm, with vesicular swellings 7 to 8 μm. Based on these morphological characteristics, the fungus was identified as Stemphylium lycopersici (Gannibal 2012). Genomic DNA was extracted and the internal transcribed spacer (ITS) regions of rDNA (569 bp) were amplified and sequenced using primers ITS1 and ITS4 (White et al. 1990). All sequences were submitted to GenBank (accession nos. KX858848, KX858850, and KX858851). BLAST search of all the sequences resulted in a 99% identity with Stemphylium lycopersici, which was recently isolated from tomato plants in China (KR911814). Leaves of five eggplant plants were sprayed with a conidial suspension (1 × 104 conidia/ml). Leaves of another set of five plants were sprayed with sterilized water. All plants were maintained in a greenhouse at 28°C with relative humidity >85%. After 3 to 5 days, inoculated plants developed symptoms similar to original diseased plants in the greenhouse, whereas control plants were symptomless. S. lycopersici is reported causing gray leaf spot disease of tomato in China (Sun et al. 2016). S. solani is also reported causing the same disease on eggplant in Malaysia (Nasehi et al. 2013). To our knowledge, this is the first report of S. lycopersici causing gray leaf spot of eggplant in China. Measures are needed to manage threat of this new disease to eggplant production in China. © 2017, American Phytopathological Society. All rights reserved.