First Report of Tomato Gray Leaf Spot Caused by Stemphylium lycopersici in Zhejiang Province, China

During the 2013 to 2014 growing season, symptoms of an unknown leaf spot were observed on tomato (Solanum lycopersicum L.) in the suburbs of Hangzhou City, Zhejiang Province, China. Diseased plants exhibited dark brown or grayish spots (1.5 to 3.3 in diameter) in early stages and a rapid wilting of the foliage occurred with disease development. Subsequently, complete defoliation took place as the disease progressed. A putative fungal pathogen was isolated from leaf lesions. Five single-spore isolates were grown on potato dextrose agar (PDA) and potato carrot agar (PCA) under light/dark cycle (12/12 h) for 8 to 12 days. Conidia were oblong with a conical end at the apex, bluntly rounded at the base, constricted at 3 (or 4) transverse septa, pale to mid brown, mostly 54 to 78 × 17 to 25 μm. All five isolates were identified morphologically as Stemphylium lycopersici (Enjoji) W. Yamam (Ellis 1971; Gannibal 2012). PCR amplification of genomic DNA using the primers ITS6 and ITS4, EF1-α (translation elongation factor 1-α), and GPDH (glyceraldehyde-3-phosphate dehydrogenase) generated sequences of approximately 650 bp, 850 bp and 950 bp, respectively. Five sequences of ITS region were submitted to GenBank (Accession Nos. KR911814, KR911815, KR911816, KR911817, and KR911818). These sequences were 100% identical to S. lycopersici isolated from tobacco (JX845139) (Kurose et al. 2014). Five sequences of the portion of EF-1α gene, Accession Nos. KR911804, KR911805, KR911806, KR911807, and KR911808, showed 99% identity with S. lycopersici isolate from chickpea (AB828254) (Hong et al. 2012). Five sequences of the portion of GPD gene, Accession Nos. KR911809, KR911810, KR911811, KR911812, and KR911813, showed 99% identity with S. lycopersici isolate from Wilford Swallowwort (KC160509) (Kurose and Hoang 2014). Conidial suspensions (106 conidia/ml) of each of the five isolates were inoculated into the leaves of greenhouse-grown (25 ± 2°C) tomato seedlings grown in pasteurized potting medium. On inoculated young leaves, small flecks were incited 3 days after inoculation, with water-soaked, brownish, depressed lesions appearing after 4 to 5 days; diseased leaves began to wilt after 2 weeks. Water-inocualted controls showed no symptoms. Stemphylium lycopersici was reisolated from foliar lesions. To our knowledge, this is the first record of gray leaf spot disease caused by S. lycopersici of tomato in Zhejiang Province, China. © 2016, American Phytopathological Society. All rights reserved.