Witch's broom

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Witch's brooms on downy birch, caused by the fungus Taphrina betulina Betula pubescens Taphrina.jpg
Witch's brooms on downy birch, caused by the fungus Taphrina betulina
Witch's broom on a white pine. Witch's broom pinus strobus.jpg
Witch's broom on a white pine.
Witch's broom in Yamaska National Park, QC WitchsBroomYamaska20200207.jpg
Witch's broom in Yamaska National Park, QC

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.

Contents

Diseases with symptoms of witches' broom, caused by phytoplasmas or basidiomycetes, are 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

Related Research Articles

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<span class="mw-page-title-main">Apical dominance</span>

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<i>Phytoplasma</i> Genus of bacteria

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<span class="mw-page-title-main">Axillary bud</span> Embryonic shoot located in the axil of a leaf or branch

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<span class="mw-page-title-main">Phyllody</span> Abnormal development of floral parts into leafy structures

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This is a glossary of some of the terms used in phytopathology.

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Moniliophthora perniciosa is a fungus that causes "witches' broom disease" (WBD) of the cocoa tree T. cacao. This pathogen is currently limited to South America, Panama and the Caribbean, and is perhaps one of the best-known cocoa diseases, thought to have co-evolved with cocoa in its centre of origin.

<i>Cacao swollen shoot virus</i> Species of virus

Cacao swollen shoot virus (CSSV) is a plant pathogenic virus of the family Caulimoviridae that primarily infects cacao trees. It decreases cacao yield within the first year of infection, and usually kills the tree within a few years. Symptoms vary by strain, but leaf discoloration, stem/root swelling, and die-back generally occur. The virus is transmitted from tree to tree by mealybug vectors. It was first discovered in Ghana in 1936, and is currently endemic in Togo, Ghana and Nigeria. Over 200 million trees have already been claimed by this disease, which has prompted Ghana to launch the most ambitious and costly eradication effort of any country in the world against a viral plant disease.

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Virescence is the abnormal development of green pigmentation in plant parts that are not normally green, like shoots or flowers. Virescence is closely associated with phyllody and witch's broom. They are often symptoms of the same disease affecting the plants, typically those caused by phytoplasmas. The term chloranthy is also sometimes used for floral virescence, though it is more commonly used for phyllody.

<i>Candidatus</i> Phytoplasma fraxini Species of bacterium

CandidatusPhytoplasma fraxini is a species of phytoplasma, a specialized group of bacteria which lack a cell wall and attack the phloem of plants. This phytoplasma causes the diseases ash yellows and lilac witches' broom.

Spruce broom rust or yellow witches' broom rust is a fungal plant disease caused by the basidiomycete fungus known as Chrysomyxa arctostaphyli. It occurs exclusively in North America, with the most concentrated outbreaks occurring in northern Arizona and southern Colorado on blue and Engelmann spruce, as well as in Alaska on black and white spruce. This disease alternates its life cycle between two hosts, with the spruce serving as the primary host and bearberry serving as the secondary or alternate host. The name for the disease comes from the distinctive “witches broom”, commonly yellow in color, which forms on the spruce after young needles have been infected. Management must be carried out through physical or mechanical methods, such as the pruning of brooms or the removal of the secondary host from the area, because no chemical control measures have yet been determined to be economically effective. Generally, spruce broom rust is seen as a mostly cosmetic issue, and it is very rarely the direct cause of tree death; however, research has shown a reduction in overall productivity and health of infected trees, making it an important issue for logging and timber companies.

Annie Gravatt was an American forest pathologist. Her areas of research included plant physiology and white pine blister rust. She also studied Chestnut blight, the fungus that devastated American chestnut trees in the early 20th century. Along with her husband, George Gravatt, she founded the community of Scientists' Cliffs, Maryland.

<i>Longan witches broom-associated virus</i> Species of virus

Longan witches broom-associated virus is a species of positive-sense single-stranded RNA virus that has not been assigned to a genus within the family Potyviridae. It is thought to be the cause of witch's broom in longan, a large tropical tree from southeastern Asia of economic value. Longan witches broom disease is a condition that was first described in 1941. The virus was found in symptomatic plants and absent in healthy plants, but not all of Koch's postulates have been fulfilled.

<i>Taphrina betulina</i> Species of fungus

Taphrina betulina is a fungal plant pathogen that causes the gall, witches broom, which is a chemical infection of birch buds or the developing shoots, leading to a proliferation of growth. It was first described by Emil Rostrup in 1883 and is found in Europe, New Zealand and North America.

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}}: 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. 1 2 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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