First Report of Southern Blight Caused by Sclerotium rolfsii on Macleaya cordata in China.

Macleaya cordata (Wild.) R. Br. (Papaveraceae) is a traditional Chinese medicinal herb distributed widely in the southeast area of China that has anti-inflammation, antimicrobial and insecticidal activities. In summer of 2014 and 2015, a commercial organic planting of M. cordata showed a soilborne disease in Yongan County, Liuyang City, Hunan Province, China. Approximately 10% of plants in the field were affected. Infected Plants exhibited dark brown lesions on the stems near the soil line. Foliage of infected plants appeared lighter green and progressively turned tan and withered. As the disease progressed, a white mycelium occurred on infected stem lesion in the presence of abundant moisture. Numerous, tan-to-brown, spherical sclerotia developed on the infected stem and on soil surfaces around the infected plants. Symptomatic basal stem sections were disinfected with 1% NaOCl solution for 1 min, rinsed in sterile water, air dried, and placed on potato dextrose agar (PDA). The cultures were incubated at 28°C in the dark. The radial mycelial growth was 15 mm/day, numerous globoid sclerotia were formed on PDA after 15 days of growth. The sclerotia (0.5 to 3 mm in diameter) were white at first and melanized, turning brown with age. The white mycelium formed a typical clamp connection structure after 5 days of growth. Aerial mycelia usually formed many narrow hyphal strands 3 to 9 μm wide. Isolates were identified as Sclerotium rolfsii on the basis of mycelial characteristics, color, and sclerotia (White et al. 1990). The internal transcribed spacer (ITS) region of rDNA was amplified using the ITS1 and ITS4 primer and the resulting sequence of 646 bp was deposited in GenBank (Accession No. KT001075) (Punja and Damiani 1996). BLAST analysis of the PCR product showed 97% identity to Athelia rolfsii (imperfect stage of S. rolfsii) (HM355751.1 and JF966208.1). To verify the pathogenicity, 60-day-old M. cordata seedlings were planted in plastic pots with sterilized mixture of peat moss and vermiculite (3:1). Each strain of 10 seedings was inoculated with 10 sclerotia of the pathogen, which was placed on the soil surface against the stem of the plant. Three other noninoculated plants served as controls. The inoculated and noninoculated plants then were placed in a greenhouse at 28 to 30°C. Ten days later, inoculated plants began to wilt. By 15 days after inoculation, 100% of the inoculated plants showed symptoms identical to those observed in the field. Meanwhile, control plants were symptomless. S. rolfsii could be reisolated from the infected plants. The experiment was repeated twice. This disease has been observed on many species of plants (Tsai 1991). To our knowledge, this is the first report of southern blight caused by S. rolfsii on M. cordata in China. © 2016 The American Phytopathological Society.