Witch's broom or witches' broom is a deformity in a
woody plant
A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposite to herbaceous plants that die back to the ground until sp ...
, typically a
tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
, 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
A broom (also known in some forms as a broomstick) is a cleaning tool consisting of usually stiff fibers (often made of materials such as plastic, hair, or corn husks) attached to, and roughly parallel to, a cylindrical handle, the broomstick. I ...
or a bird's
nest
A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...
. It is sometimes caused by pathogens.
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
''Theobroma cacao'', also called the cacao tree and the cocoa tree, is a small ( tall) evergreen tree in the family Malvaceae. Its seeds, cocoa beans, are used to make chocolate liquor, cocoa solids, cocoa butter and chocolate. The largest pr ...
'',
jujube (''Ziziphus jujuba'') and the timber tree ''
Melia azedarach''.
Causes
A tree's characteristic shape, or habit, is in part the product of
auxin
Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...
s, 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
Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and lea ...
, a
phytohormone which interferes with growth regulation. The phenomenon can also be caused by other organisms, including
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
,
oomycetes, insects,
mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...
s,
nematode
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...
s,
phytoplasmas, and
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
es.
[''Book of the British Countryside''. Pub. London : Drive Publications, (1973). p. 519.] 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.
Ecological role
Witches' brooms provide nesting habitat for birds and mammals, such as the
northern flying squirrel, which nests in them.
See also
*
Plant development § buds and shoots – atypical shoot development
*
Epicormic shoot
An epicormic shoot is a shoot growing from an epicormic bud, which lies underneath the bark of a trunk, stem, or branch of a plant.
Epicormic buds lie dormant beneath the bark, their growth suppressed by hormones from active shoots higher up t ...
– a shoot that develops from buds under the bark
*
Forest pathology
* ''
Longan witches broom-associated virus
''Longan witches broom-associated virus'' (LWBD or LWBaV) 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 ...
''
* ''
Melampsora
''Melampsora'' is a genus of Basidiomycota
Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are ...
'' can cause different kinds of witch's brooms.
* ''
Moniliophthora perniciosa'', cause of witch's broom disease in cacao
*
Phyllody, a related plant growth abnormality affecting flowers
References
External links
{{commonscat-inline, Witch's broom
Witches' Broomat
BBC h2g2.
Fir and spruce broom
Plant pathogens and diseases