Identification and Characterization of Sclerotium delphinii Causing Southern Blight on Aconitum kusnezoffii in Northeast China

Abstract

Aconitum kusnezoffii is a perennial medicinal plant belong to the Ranunculaceae family and distributed mainly in Northeast and North China. In July of 2018, a typical southern blight disease of A. kusnezoffii was observed in commercial fields of Qingyuan County, Fushun City, Liaoning Province, China. The fungus mainly infected stem base and tuberous roots of the plant by wrapping the hyphae and absorbing nutrition, resulting in tuberous root wilted or whole plant death. Morphological characteristics of colony and sclerotia of three representative strains isolated from the diseased plants differed obviously from those of Sclerotium rolfsii isolated from A. carmichaeli. Sclerotia were large (0.8-5.1 mm size), reddish-brown, irregular and pitted surfaces, and the hyphae was white, compact or fluffy, with a growth rate ranging from 8.0 mm/d to 10.1 mm/d. Phylogenetic analysis of the internal transcribed spacer and the large subunit sequences showed that three strains isolated from A. kusnezoffii formed a unique and well supported clade that groups with the reference isolates of S. delphinii. Based on phylogentic analysis, cultural and morphological characteristics, the three isolates of A. kusnezoffii were identified as S. delphinii. The optimum temperature for mycelial growth of the three tested isolates were 30℃ and sclerotia formed and matured more easily at 20℃. Light promoted the growth of mycelial, while dark was beneficial to the formation and maturation of sclerotia. The pathogenicity of S. delphinii showed stronger than S. rolfsii at low temperature (20℃). This is the first report of S. delphinii causing southern blight on A. kusnezoffii in China and this finding would provide a basis for disease accurate diagnosis and the development of effective management strategies.