Nectria radicicola

Nectria radicicola is a plant pathogen that is the causal agent of root rot[1] and rusty root.[2] Substrates include ginseng[3] and Narcissus. It is also implicated in the black foot disease of grapevine. It is of the genus Nectria and the family Nectriaceae. N. radicicola is recognizable due to its unique anatomy, morphology, and the formation of its anamorph Cylindrocarpon desructans.[4]

Nectria radicicola
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Sordariomycetes
Order: Hypocreales
Family: Nectriaceae
Genus: Nectria
Species:
N. radicicola
Binomial name
Nectria radicicola
Gerlach & L. Nilsson (1963)
Synonyms

Cylindrocarpon destructans
Cylindrocarpon radicicola
Fusarium rhizogenum
Neonectria radicicola
Ramularia destructans
Septocylindrium aderholdii Ilyonectria radicicola

Distribution and habitat

N. radicicola is currently distributed evenly alongside its primary substrates American ginseng, Panax quinquefolius, and Korean ginseng, Panax ginseng.[2] It occurs throughout North America and continental Asia, primarily Korea and China. It can alternate between growing with a host or remaining dormant as chlamydospores for years at a time if none is present. Because the spores are able to effectively overwinter in plant debris and soil, N. radicicola is not limited by seasonally colder climate conditions.[5]

Life cycle

N. radicicola is a species complex of organisms which target the roots of various species of ginseng, grapevines, and some young trees as their primary substrate.[6][7] The primary vector of infection are the chlamydospores which might survive for years in the soil before detecting and subsequently infecting a new host organism. Upon infecting the host organism hyphae begin to grow inter and intracellularly which subsequently causes the plant tissues to begin to rot. More chlamydospores will form once the hyphae reach the surface of the host tissue where micro and macronidia will sprout and release the spores.

Symptoms of infection of host plants

Root rot

After contracting root rot from N. radicicola, the plant will begin to wilt and eventually become discolored, transitioning from red-orange to brown-black with an accompanying strong odor resulting from the rot. The discoloration and odor may be localized only to lesions on the base of the stem and roots or spread across most of the plant. The roots will eventually dry out and become scaly and shriveled. In time the infection may invite secondary infections to take hold in addition to that from the N. radicicola from non-pathogenic sources. [8][2]

Rusty root

Rusty root usually presents as slightly raised rust-colored spots at the crown of the taproot which will then spread to cover part or all of the root. The symptoms are only present on the surface of the root however and the discolored spots can be scraped off to reveal healthy tissue beneath. Rusty root is a less severe disease than root rot, with a much lower chance of inflicting serious long-lasting damage or death on the host plant and is associated with the less aggressive strains of the N. radicicola complex.[2]

Newly burgeoning research

Double-stranded RNA makeup and virality

Research has shown that the virality of the N. radicicola is variable and highly dependent on the makeup of the double stranded RNA within the genotype. Phenotypic features which were closely related to virality such as laccase activity and sporulation were highly dependent on the amount and type of dsRNA present in the genome. This may indicate that the size of dsRNA present in a strain is a key indicator for viral success in different strains of the N. radicicola population.[9][10]

Possible species separation between rusty root and root rot development

It has been observed that rusty root and root rot may either be inflicted on host plants, specifically various forms of ginseng, after contracting N. radicicola. Due to the increased severity of a root rot infection over rusty root, the strains which cause root rot are considered to be the more aggressive of the variations. New research suggests that the symptoms may actually arise from two different species rather than just the N. radicicola but rather that It has been observed that rusty root and root rot may either be inflicted on host plants, specifically ginseng, after contracting N. radicicola and due to the added severity, the strains which cause root rot are considered the more aggressive of the variations. Research suggests that the symptoms may actually arise from two different species rather than just the N. radicicola. Ilyonectria mors-panacis may be responsible for the root rot while the N. radicicola might only result in the observed rusty root. As the name suggests, Ilyonectria mors-panacis is closely related to Nectria radicicola, also known as Ilyonectria radicicola, but the genetic discrepancies between plants observed with root rot and rusty root are significant enough that what was thought to be merely different strains might actually be classified as arising from two different species of fungus.[2]

References
  1. Kang Y, Kim MR, Kim KH, Lee J, Lee SH. Chlamydospore Induction from Conidia of Cylindrocarpon destructans Isolated from Ginseng in Korea. Mycobiology. 2016 Mar;44(1):63-5. doi:10.5941/MYCO.2016.44.1.63. Epub 2016 Mar 31. PMID: 27103857; PMCID: PMC4838594.
  2. Farh ME, Kim YJ, Kim YJ, Yang DC. Cylindrocarpon destructans/Ilyonectria radicicola-species complex: Causative agent of ginseng root-rot disease and rusty symptoms. J Ginseng Res. 2018 Jan;42(1):9-15. doi:10.1016/j.jgr.2017.01.004. Epub 2017 Jan 16. PMID: 29348716; PMCID: PMC5766697.
  3. Wang J, Chen H, Gao J, Guo J, Zhao X, Zhou Y. Ginsenosides and ginsenosidases in the pathobiology of ginseng-Cylindrocarpon destructans (Zinss) Scholten. Plant Physiol Biochem. 2018 Feb;123:406-413. doi:10.1016/j.plaphy.2017.12.038. Epub 2017 Dec 29. PMID: 29306188.
  4. Gary J. Samuels, David Brayford, Variation in Nectria radicicola and its anamorph, Cylindrocarpon destructans, Mycological Research, Volume 94, Issue 4, 1990, Pages 433-442, ISSN 0953-7562, doi:10.1016/S0953-7562(10)80001-2.
  5. Jin X, Guo L, Jin B, Zhu S, Mei X, Wu J, Liu T, He X. Inhibitory mechanism of 6-Pentyl-2H-pyran-2-one secreted by Trichoderma atroviride T2 against Cylindrocarpon destructans. Pestic Biochem Physiol. 2020 Nov;170:104683. doi:10.1016/j.pestbp.2020.104683. Epub 2020 Aug 20. PMID: 32980051.
  6. Ka, S., McMullen, C., Yee, D., Reeleder, R. D., & Dobinson, K. F. (2003). Molecular Differentiation and Detection of Ginseng-Adapted Isolates of the Root Rot Fungus Cylindrocarpon destructans. Phytopathology, 93(12), 1533–1542. doi:10.1094/phyto.2003.93.12.1533
  7. Mirrington RN , Ritchie E , Shoppee CW , Sternhell S Taylor WC (1966) Some metabolites of Nectria radicicola Gerlach & Nilsson (syn. Cylindrocarpon radicicola Wr.): The structure of radicicol (monorden) . Australian Journal of Chemistry 19, 1265-1284.
  8. Bischoff Nunes, I.; Goodwin, P.H. Interaction of Ginseng with Ilyonectria Root Rot Pathogens. Plants 2022, 11, 2152. doi:10.3390/plants11162152
  9. Ahn, I., & Lee, Y. (2001). A Viral Double-Stranded RNA Up Regulates the Fungal Virulence of Nectria radicicola. Molecular Plant-microbe Interactions, 14(4), 496–507. doi:10.1094/mpmi.2001.14.4.496
  10. Song JY, Seo MW, Kim SI, Nam MH, Lim HS, Kim HG. Genetic Diversity and Pathogenicity of Cylindrocarpon destructans Isolates Obtained from Korean Panax ginseng. Mycobiology. 2014 Jun;42(2):174-80. doi:10.5941/MYCO.2014.42.2.174. Epub 2014 Jun 30. PMID: 25071387; PMCID: PMC4112234.

Bibliography
  • Boerema, G. H.; Hamers, Maria E. C. (May 1989). "Check-list for scientific names of common parasitic fungi. Series 3b: Fungi on bulbs: Amaryllidaceae and Iridaceae". Netherlands Journal of Plant Pathology. 95 (S3): 1–29. doi:10.1007/BF01981520. S2CID 9422139.


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