Fusarium oxysporum f. sp. cubense

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Fusarium oxysporum f. sp. cubense
Systematics
Subclass : Hypocreomycetidae
Order : Crust ball mushrooms (Hypocreales)
Family : Pustel mushroom relatives (Nectriaceae)
Genre : Fusarium
Type : Fusarium oxysporum
forma specialis : Fusarium oxysporum f. sp. cubense
Scientific name
Fusarium oxysporum f. sp. cubense
( EF Smith ) Snyder & Hansen

Fusarium oxysporum f. sp. cubense is a forma specialis that different sac fungi from the Fusarium oxysporum - complex of species summarizes. Fusarium oxysporum f. sp. cubense forms whitish to purple mycelium , which spreads asexually via the formation of conidiospores . It affects various types of bananas ( Musa spp.) And causes Panama disease , a form of fusariosis ,in them. Infestation with the fungus manifests itself in a red-brown discoloration of the xylem of the host plant, followed by yellowdiscoloration, wilting and longitudinal splitting of the leaves. Fusarium oxysporum f. sp. cubense probably originates from Southeast Asia and spread through Australia in the tropics of the Old and New World. It is divided into four host-specific races, their systematic relations both among themselves and with other Fusarium - taxa are complex. In addition to individual mutation , the four races probably alsoevolvedthrough horizontal gene transfer and parasexual gene exchange.

morphology

Morphologically, Fusarium oxysporum f. sp. cubense (Foc) does not differ from other F. oxysporum forms. In nutrient solutions made from potato starch and at temperatures of 24 ° C, cultures of the fungus grow 4 to 7 mm per day and form white to purple, superficial mycelium . Its sporodochia are brownish to orange, its sclerotia blue and are formed below the substrate surface. F. oxysporum f. sp. cubense forms micro- and macroconidia via monophialids . The microconidia of the fungus arise from false heads and measure 5–16 × 2.4–3.5  µm . They consist of one or two cells and are oval to kidney-shaped. The sickle-shaped macroconidia reach sizes of 27–55 × 3.3–5.5 µm. They have four to eight cells, with the most basal cell shaped like a foot. The fungus forms chlamydospores that serve to survive. They arise individually or in pairs on the end cells and intermediate segments of hyphae and conidia, are spherical and have a diameter of 7-11 µm.

Infestation symptoms

An infection with Fusarium oxysporum f. sp. cubense is initially noticeable in the roots, where it is characterized by a discoloration of the xylem into red-brown. The discoloration continues from there into the rhizome and is most pronounced at the contact point between the bark and vascular bundles . Later it also becomes noticeable in large parts of the pseudo-strain. In the final stage of the infestation, the oldest leaves of the host plant first turn yellow and split in the middle. Little by little, younger leaves also show symptoms in the form of yellowing and wilting. As a result of the infestation, the plant usually dies and no longer produces any fruit, which can lead to a complete loss of the harvest, especially in monocultures that are already susceptible to damage.

Reproduction and Distribution

For Fusarium oxysporum f. sp. cubense is not known to be a major fruit that sexually produces spores. However, genetic similarities to otherwise more distant relatives suggest that mechanisms exist or existed for the fungi that enable the recombination of DNA. It is unclear whether this is sexual reproduction via a main fruit form or parasexual fusion of DNA strands (e.g. through the union of compatible mycelium). The usual reproduction strategy of the fungus, however, consists in the formation of conidia, which are pinched off by hyphae. They germinate in a new mycelium when they fall on a suitable substrate. They can remain fertile for up to 30 years and possibly also survive on plants that are not part of their actual host range. The mycelium and conidia can spread through cuttings, but also through running water or through the ground. In addition, tools and machines are often vectors for the fungus on plantations.

Taxonomy and systematics

Fusarium oxysporum f. sp. cubense was first described in 1910 by Erwin Fink Smith as Fusarium cubense and in 1940 by William Cowperthwaite Snyder and Hans Nicholas Hansen of a species in a forma specialis of Fusarium oxysporum . Both of them justified this step by stating that all the forms assigned to the newly conceived F. oxysporum were morphologically indistinguishable and could only be identified by their hosts. The classification of F. oxysporum f. sp. To this day, cubense has proved difficult because the samples and specimens contained underneath cannot be assigned a uniform relationship. Several conflicting results from molecular biology studies suggest that the genome of the samples is composed of many different sources. Neither from a morphological nor from a phylogenetic point of view should it be possible to delimit the taxon in a meaningful way. An additional problem is the concept of forma specialis , the only taxonomic characteristic of which is the attachment to a particular host.

On the basis of their hosts, F. oxysporum -f.-sp.- cubense strains are divided into four different races:

  • Race 1: Affects the banana varieties ' Gros Michel ', 'Silk', 'Pome' and 'Pisang awak'. By 1960 it destroyed the entire stock of Gros Michel in export-oriented plantations in Central America, starting from Panama, which is why the disease that the fungus produces in bananas is also known as 'Panama disease '.
  • Race 2: Affects the ' Bluggoe ' banana variety and other related ABB plantains.
  • Race 3: Affects various Heliconia species, probably not closely related to the other races, and is no longer recognized as a banana pest.
  • Race 4: Affects ' Cavendish ', like all banana varieties that are attacked by races 1 and 2. Initially, only the Foc strains that attacked ' Cavendish ' in the subtropics (Australian, Canary Islands and South Africa) under stressful situations (especially cold) were designated as race 4. These strains are now classified as subtropical race 4 (STR4) to distinguish them from the strains that infest 'Cavendish' bananas in the tropics. After 1990, more and more tropical Cavendish plantations in Southeast Asia were infested and a new strain, Tropical Race 4 (TR4) of Foc, was identified as the pathogen.

By the end of 2015, TR4 was identified in the following regions:

  • Australia (Northern Territory and Queensland)
  • China (Hainan, Hunan, Guandong and Guangxi)
  • Indonesia (Bali, Halmahera, Kalimantan, Java, Papua Province, Sulawesi and Sumatra)
  • Jordan
  • Lebanon
  • Malaysia (mainland and Sarawak)
  • Mozambique
  • Oman
  • Pakistan
  • Philippines (Mindanao)
  • Taiwan

In mid-2019, the Colombian authorities reported an infestation with TR4 in La Guajira in the north of the country.

swell

literature

  • Gerda Fourie, ET Steenkamp, ​​Randy C. Ploetz, TR Gordon, A. Viljoen: Current status of the taxonomic position of Fusarium oxysporum formae specialis cubense within the Fusarium oxysporum complex . In: Infection, Genetics and Evolution . tape 11 (3) , 2011, pp. 533-542 , doi : 10.1016 / j.meegid.2011.01.012 .
  • Kerry O'Donnell, Cécile Gueidan, Stacy Sink, Peter R. Johnston, Pedro W. Crous, Anthony Glenn, Ron Riley, Nicholas C. Zitomer, Patrick Colyer, Cees Waalwijk, Theo van der Lee, Antonio Moretti, Seogchan Kang, Hye -Seon Kim, David M. Geiser, Jean H. Juba, Robert P. Baayen, Matthew G. Cromey, Sean Bithell, Deanna A. Sutton, Kerstin Skovgaard, Randy Ploetz, H. Corby Kistler, Monica Elliott, Mike Davis, Brice AJ Sarve: A two-locus DNA sequence database for typing plant and human pathogens within the Fusarium oxysporum species complex . In: Fungal Genetics and Biology . tape 46 (12) , 2009, pp. 936-948 , doi : 10.1016 / j.fgb.2009.08.006 .
  • Randy C. Ploetz: Fusarium Wilt of Banana Is Caused by Several Pathogens Referred to as Fusarium oxysporum f. sp. cubense . In: Phytopathology . tape 96 (6) , 2006, pp. 653-656 , doi : 10.1094 / phyto-96-0653 .
  • William Cowperthwaite Snyder, Hans Nicholas Hansen: The Species Concept in Fusarium . In: American Journal of Botany . tape 27 (2) , 1940, pp. 64-67 .

Individual evidence

  1. ↑ a b Ploetz 2006, p. 654.
  2. ↑ a b c Ploetz 2006, p. 653.
  3. ↑ Fourie et al. 2011, p. 539.
  4. ↑ Snyder & Wollenweber 1940, pp. 65-66.
  5. ↑ Fourie et al. 2011, pp. 539-540.
  6. ↑ O'Donnel et al. 2009, p. 946.
  7. ↑ http://www.promusa.org/Fusarium+oxysporum+f.+sp.+cubense
  8. ↑ http://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-04-15-0101-RVW
  9. ↑ http://www.annualreviews.org/doi/pdf/10.1146/annurev-phyto-080614-120305
  10. ↑ http://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-04-15-0101-RVW
  11. ↑ Florian Gehm: Bananas: "Tropical Race" fungus attacks plantations in Colombia. In: welt.de . August 13, 2019, accessed August 14, 2019 .
  12. ↑ Philipp Felber-Eisele: Because of fungal disease: will we soon pay more for bananas? In: bernerzeitung.ch . August 15, 2019, accessed August 16, 2019 .
  13. ↑ Kathrin Zinkant: The Curse of Panama . In: Tages-Anzeiger . Zurich September 5, 2019, p. 38 .