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.
For the nebula, see Witch's Broom Nebula.
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

A tree's characteristic shape, or habit, is in part the product of auxins, hormones which control the growth of secondary apices. The growth of an offshoot is limited by the auxin, while that of the parent branch is not. In cases of witch's broom, the normal hierarchy of buds is interrupted, and apices grow indiscriminately. This can be caused by cytokinin, a phytohormone which interferes with growth regulation. 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. If twigs of witch's 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 nests 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 habitat in the boreal forest of Alaska" (pdf). Alaska Department of Fish and Game. pp. 18–19. Retrieved 2 June 2020.

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