Abstract
Panax ginseng rusty root rot caused by the Ilyonectria species complex is a devastating disease, and it is one of the main factors contributing to the difficulty in continual cropping. Rusty root rot occurs in all ginseng fields, but little is known about the taxonomy of the fungal pathogen complex, especially Ilyonectria and Ilyonectria-like species. Rusty root rot samples were collected from commercial ginseng cultivation areas of China, and the pathogens were isolated and purified as single spores. Based on the combination analysis of multiple loci (rDNA-ITS, TUB, HIS3, TEF, ACT, LSU, RPB1, RPB2, and SSU) and morphological characteristics, the pathogens causing ginseng rusty root rot were determined. Fungal isolates were obtained from infected roots in 56 locations within main cultivation areas in China. A total of 766 strains were identified as Ilyonectria, Ilyonectria-like and Rhexocercosporidium species, including I. robusta (55.0%), I. communis (21.7%), I. mors-panacis (10.9%), I. pseudodestructans (2.0%), I. changbaiensis (1.3%), I. qitaiheensis (1.3%), Neonectria obtusispora (2.0%), Dactylonectria torresensis (0.5%), D. sp. (0.5%), and R. panacis (1.5%), and four novel species, Thelonectria ginsengicola (1.0%), T. jixiensis (1.0%), T. mulanensis (0.8%) and T. fusongensis (0.5%), with a total of 14 species. As the pathogen present in the highest proportion, I. robusta was the most prevalent and damaging species, unlike the pathogens reported previously. All of the examined strains were proven to cause ginseng rusty root rot. Our results indicate that the taxonomy of the fungal complex associated with ginseng rusty root rot includes Ilyonectria, Ilyonectria-like genera (Dactylonectria, Neonectria, and Thelonectria) and Rhexocercosporidium.
Highlights
Panax ginseng is one of the most cultivated medicinal plants in China, and the quality of ginseng greatly influences the quality of cosmetics, health care products and medicines that use ginseng as a raw material (Baranov, 1966; Hu, 1977)
Four novel species are named in this article: T. ginsengicola (1.0%), the type strain is R9; T. jixiensis (1.0%), the type strain is Q21-5; T. mulanensis (0.8%), the type strain is Q20-8 and T. fusongensis (0.5%), the type strain is R1-8
R. panacis was the only pathogen except Ilyonectria-like that was present at an abundance of 1.5%.I. communis, I. pseudodestructans, I. changbaiensis, I. qitaiheensis, N. obtusispora, D. torresensis, T. jixiensis, T. mulanensis, T. fusongensis and T. ginsengicola were first reported to cause ginseng rusty root rot
Summary
Panax ginseng is one of the most cultivated medicinal plants in China, and the quality of ginseng greatly influences the quality of cosmetics, health care products and medicines that use ginseng as a raw material (Baranov, 1966; Hu, 1977). Ginseng rusty root rot is caused by Ilyonectria/Cylindrocarpon or Ilyonectria/Cylindrocarpon-like species, and it is the most. Taxonomy of Rusty Root Rot Pathogens devastating chronic disease and the greatest threat to ginseng (Panax ginseng) cultivation (Guan et al, 2020). Rusty root rot may cause 30% loss of ginseng, and it can be found in all ginseng planting areas. Rusty root rot has always been one of the important factors that interferes with the maintenance of continuous ginseng cropping. The incidence of rusty root rot in 2-year-old ginseng continuous cropping is 95.8% (Cho et al, 1995). The appearance of ginseng root rot and the degree of damage greatly influence the value of ginseng (Zhou et al, 2017). Ilyonectria and Ilyonectria-like species are commonly associated with rot and decay of woody and herbaceous plants (Domsch et al, 2007)
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