Witch's broom

Witch's broom or witches' broom is a deformity in a woody plant, typically a tree, where the natural structure of the plant is changed. A dense mass of shoots grows from a single point, with the resulting structure resembling a broom or a bird's nest. It is sometimes caused by pathogens.

Not to be confused with Mistletoes, which are not the host plant's own tissue, but parasitic plants growing on the host.
For a broom associated with witches, see Besom.
Witch's brooms on downy birch, caused by the fungus Taphrina betulina
Witch's broom on a white pine.

Witch-broom disease, caused by phytoplasmas or basidiomycetes, is economically important in a number of crop plants, including the cocoa tree Theobroma cacao,[1] jujube (Ziziphus jujuba)[2] and the timber tree Melia azedarach.[3]

Causes

Witch's broom can be caused by cytokinin, a phytohormone, interfering with an auxin-regulated bud. In normal plant function, an auxin would keep the secondary, tertiary, quaternary, etc. tips from overgrowing, but cytokinin can sometimes interfere with this control, causing these apices to grow into witch's brooms. The phenomenon can also be caused by other organisms, including fungi, oomycetes, insects, mites, nematodes, phytoplasmas, and viruses.[4] The broom growths may last for many years, typically for the life of the host plant. Human activity is sometimes behind the introduction of these organisms, for example, by failing to observe hygienic practice and thereby infecting the tree with the causative organism, or by pruning a tree improperly, and thereby weakening it. If twigs of witches' brooms are grafted onto normal rootstocks, freak trees result, showing that the attacking organism has changed the inherited growth pattern of the twigs.[4]

Ecological role

Witches' brooms provide nesting habitat for birds and mammals, such as the northern flying squirrel, which nest in them.[5][6]

See also

References
  1. Purdy, L.H.; Schmidt, R.A. (1996). "Status Of Cacao Witches' Broom: Biology, Epidemiology, and Management". Annual Review of Phytopathology. 34 (1): 573–594. doi:10.1146/annurev.phyto.34.1.573. PMID 15012557.
  2. Li Yun; Wang Yu; Tian Yanting & Sun Haoyuan (2001). "Advances in Tissue Culture and Eliminating of the Pathogeny of Witch Broom Disease(MLO) of Chinese Jujube". Cite journal requires |journal= (help)
  3. Gomez, G.G.; Conci, L.R.; Ducasse, D.A.; Nome, S.F. (1996). "Purification of the Phytoplasma Associated with China-tree (Melia azedarach L.) Decline and the Production of a Polyclonal Antiserum for its Detection". Journal of Phytopathology. 144 (9–10): 473–477. doi:10.1111/j.1439-0434.1996.tb00327.x.
  4. Book of the British Countryside. Pub. London : Drive Publications, (1973). p. 519.
  5. Mowry, Robert A. (2008). "Northern Flying Squirrel" (pdf). Alaska Department of Fish and Game. Retrieved 2 June 2020.
  6. Paragi, Thomas; Rodman, Sue (2020). "Maintaining wildlife habitatin the boreal forest of Alaska" (pdf). Alaska Department of Fish and Game. pp. 18–19. Retrieved 2 June 2020.

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