First Report of Greenhouse Tomato Wilt Caused by Plectosphaerella cucumerina in China

Tomato (Lycopersicon esculentum Mill.) is one of the most important vegetable crops in China. In May 2011, root rot and plant wilt were observed on tomato plants (variety Jinguan No. 5 and Meina) in 26 commercial greenhouses in Huludao city, Liaoning Province, China. Disease incidence was 30 to 95%. At beginning of fruit set, symptoms were chlorosis of lower leaves and lack of turgidity in young leaves. Severely affected plants were wilted and stunted as fruit approached maturity. Primary and secondary roots became necrotic with few fine feeder roots. Symptomatic roots were collected and cut into small pieces, disinfested in 2% sodium hypochlorite for 2 min, rinsed with sterile water, and placed on potato dextrose agar. After incubation at 25°C for 5 days, 20 axenic cultures were obtained from single conidia. Colonies were buff or salmon pink, moist, and had appressed, slimy mycelium. Aerial mycelium was sparse with simple or branched conidiophores. Conidia were 4.0 to 8.9 × 2.0 to 4.0 (average 6.9 × 2.8) μm, aggregated in slimy heads, hyaline ellipsoidal and ovoid, smooth, and 0 to 1 septate. Conidia were borne on phialides that were 6.3 to 24.3 × 1.4 to 3.3 (average 15.9 × 2.2) μm. These characteristics are typical of Plectosphaerella cucumerina (Lindf.) W. Gams (1) (anamorph: Fusarium tabacinum) (3). The internal transcribed spacer (ITS) region of the 20 isolates was amplified using the primers ITS1/ITS4 and sequenced. Identical sequences were obtained from all 20 isolates, and the sequence of isolate HLDT15 was submitted to GenBank (Accession No. KC894931). BLAST analysis of the sequence showed 100% similarity to P. cucumerina (AB469880). Pathogenicity tests were conducted with tomato variety Jinguan No. 5. Six 12-liter pots were filled with sterilized potting mix (equal parts sand, peat, and soil) and 200 ml conidial suspension (1 × 10⁵ conidia ml–¹). The conidial suspension of the isolate of P. cucumerina was prepared from 7-day-old cultures grown in potato dextrose broth on a shaker (120 rpm) at 25 ± 1°C. Six control pots were filled with potting mix and 200 ml of sterilized potato dextrose broth. Each pot was sown with six surface-sterilized (2% sodium hypochlorite for 2 min) tomato seeds. All the pots were kept in a greenhouse at 23 to 28°C. Three to four weeks after seedling emergence, all inoculated plants were dwarfed and lower leaves were chlorotic. Roots were necrotic and produced fewer fibrous roots. All characteristics were similar to original observations on the host of origin. Control plants remained asymptomatic. The same results were obtained when pathogenicity tests were repeated twice. P. cucumerina was reisolated from inoculated plants and matched the morphological and molecular characteristics of the original isolates. P. cucumerina was reported as a pathogen of tomato in Italy (2) and Australia (4). To our knowledge, this is the first report of P. cucumerina causing tomato wilt in China. So far, we have observed the disease on tomatoes in commercial greenhouses of Pulandian and Panjin city, Liaoning Province, China. The spread of this disease may pose a threat to tomato production in China.References: (1) A. Carlucci et al. Persoonia 28:34, 2012. (2) A. Matta et al. Riv. Patol. Veg. 14:119, 1978. (3) M. E. Palm et al. Mycologia, 87:397, 1995. (4) I. G. Pascoe et al. Mycol. Soc. 83:343, 1984.