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First Report of Sclerotium rolfsii var. delphinii Causing Southern Wilt of Pseudostellaria heterophylla in China

Wu, L. K., Xiao, Z. G., Li, M. L., Wang, J. Y., Yang, B., Chen, J., Tong, Q. Y., Lin, W. X.
Plant disease 2019 v.103 no.6 pp. 1419
Athelia rolfsii, Caryophyllaceae, DNA primers, Oriental traditional medicine, Sclerotium (genus), color, computer software, diabetes, fungi, herbaceous plants, leaves, mycelium, pathogenicity, phylogeny, roots, sclerotia, seedlings, soil, stems, tissues, China
Pseudostellaria heterophylla (family Caryophyllaceae) is a perennial herbaceous plant. Its tuberous roots are highly valued in traditional Chinese medicine. The medicine has multiple pharmacological actions in curing inappetence, debility, diabetes, and weakness (Hua et al. 2016). A severe rot disease (3.4 to 8.1% incidence) was observed in basal stem and root portions of P. heterophylla in Ningde City (27°08′ N, 119°88′ E), Fujian Province, during 2016. Infected plants displayed water soaked lesions on leaves, stem bases, and roots. Whitish abundant mycelia with light or reddish brown sclerotia were seen on affected leaves, basal stems, roots, and surrounding soil. The fungus was consistently isolated from the symptomatic tissues on potato dextrose agar (PDA) medium. The mycelial growth on PDA was 14 to 17 mm/day and the white, cottony mycelia covered the entire surface of the PDA plate after 5 days of incubation at 30°C. Whitish sclerotial bodies appeared after 8 days of incubation. Sclerotia were globose and tan or light to dark brown in color. The number of sclerotia per plate ranged from 10 to 38 (mean 24 ± 14, n = 3). The sclerotia varied greatly in size, with an average diameter of 2.58 mm. Irregular sclerotia with surface markings ranging from 1.1 × 2.5 mm to 2.4 × 4.0 mm across were observed, in line with the previous studies (Mukherjee et al. 2015; Punja and Damiani 1996; Stevens 1931). Further, the internal transcribed spacer (ITS) region of the fungus was amplified by using primer pairs ITS1F and ITS4 and then subjected to sequencing. nBLAST search analysis showed sequences from four isolates were 100% similar and shared 99% homology with Sclerotium delphinii (strain CBA-HW05, GenBank accession no. GU567775.1). Phylogenetic tree analysis with MEGA 4.1 software confirmed that the fungal isolate clustered with S. delphinii strain CBA-HW05 (GU567775.1). Based on morphological and molecular characteristics, the causal agent was identified as S. rolfsii var. delphinii. The sequence was deposited in GenBank (accession no. MK073010). Pathogenicity tests were conducted using 35-day-old tissue culture-raised seedlings. Three seedlings were inoculated with 5-day-old PDA-grown mycelia of the fungal isolate. The experiment was repeated three times. All nine S. rolfsii var. delphinii-inoculated seedlings showed typical disease symptoms after 9 days of inoculation. The pot experiment further demonstrated the high pathogenicity of isolate W-SD6 to the potted seedlings of P. heterophylla. An associated fungal pathogen was consistently reisolated from the inoculated seedlings and its identity was established. Though S. rolfsii var. delphinii is known to cause stem and collar rot in many herbaceous plants (Mukherjee et al. 2015; Wang et al. 2017; Xu et al. 2008), to the best of our knowledge, this is the first report of southern wilt on P. heterophylla caused by S. rolfsii var. delphinii in China. There is a need to develop effective management measures to reduce the occurrence of this disease.