Witch's broom
A witch's broom or witches' broom is a disease or 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.
Witch-broom disease caused by phytoplasmas 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. Usually auxin would keep the secondary, tertiary, and so on apexes from growing too much, but cytokinin releases them from this control, causing these apexes to grow into witch's brooms.
Witch's may be caused by many different types of organisms, including fungi, oomycetes, insects, mistletoe, dwarf mistletoes, mites, nematodes, phytoplasmas or 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.[citation needed]
Uses
Witches' brooms occasionally result in desirable changes. Some cultivars of trees, such as Picea orientalis 'Tom Thumb Gold', were discovered as witch's brooms. 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]
Witches' brooms are of wide ecological importance. They generally tend to be inhabited by a wide variety of organisms apart from the causative organisms. Some of the invading organisms, such as some species of moths, are specific to particular types of witches' brooms, relying on them for food and shelter for their larvae. Various larger animals nest in them, including the northern flying squirrel.[5]
See also
- Phyllody, a related plant growth abnormality affecting flowers
- Witch's Broom Nebula
- Moniliophthora perniciosa, cause of Witch's broom disease in cacao
- Epicormic shoot, shoots that develop from buds under the bark
- Adventitiousness, shoots that develop in unusual places
- In Toronto, the term witch's broom is used to refer to the trolley pole on local streetcars.[6]
- Forest pathology
References
- ^ 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.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Li Yun, Wang Yu, Tian Yanting, and Sun Haoyuan (2001). "Advances in Tissue Culture and Eliminating of the Pathogeny of Witch Broom Disease(MLO) of Chinese Jujube".
{{cite journal}}: Cite journal requires|journal=(help)CS1 maint: multiple names: authors list (link) - ^ 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.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ a b Book of the British Countryside. Pub. London : Drive Publications, (1973). p. 519.
- ^ "Home Page, Alaska Department of Fish and Game". Adfg.state.ak.us. 2012-01-01. Retrieved 2012-05-26.
- ^ Micallef, Shawn (2008-09-14). "Red Rockets: I love to love you but sometimes it ain't easy « Spacing Toronto". Spacingtoronto.ca. Retrieved 2012-05-26.
External links
Media related to Witch's broom at Wikimedia Commons
- Witches' Broom links to an article about witches' brooms on the BBC h2g2 website.