Galls and Rusts List 

WITCH'S BROOM

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Twigs:
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A GALL ON A TREE

 Galls and Rusts Menu

2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
This tree has about 90 manifestations of Witch's Broom, some much larger than others.


2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
From afar they look like birds nests, and indeed, some are used as nests - for Northern Flying Squirrels - but not in the UK.


2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
The largest are up to a metre across and can also look like Mistletoe.


2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
The largest are very dense, consisting of a profusion of fairly straight but branched twigs growing from the stock tree host, and indeed, they are part of the tree, but a part which has been forced into an abnormal growth pattern by an infestation.


2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
This is an old one which is coated in some green lichen. The twigs have a profusion of buds from which abnormal leaves and more twigs will grow. The largest are dense enough to block all light.


2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
A small one. An ordinary branch starts sprouting a plethora of extra twigs.


20th March 2015, Middlewood Way, Wood Lanes, Cheshire. Photo: © RWD
The twigs are mainly straight, but highly branched.


2nd May 2013, moors, Goyt's Bridge, Derbyshire. Photo: © RWD
A plethora of buds about to sprout yet more branches and leaves.


20th March 2015, Middlewood Way, Wood Lanes, Cheshire. Photo: © RWD
Highest density of twiglets in the centre.


20th March 2015, Middlewood Way, Wood Lanes, Cheshire. Photo: © RWD
The twigs are otherwise completely normal, with leaf buds.


Easily confused with : Mistletoe (Viscum album) which, from afar, also looks like birds nests in various trees.

Not to be semantically confused with : Witch-Hazel [a tree with similar name] nor with Broom (Cytisus scoparius) nor with Butcher's Broom (Ruscus aculeatus) [shrubs with similar names].

No relation to : Bird's-Nest Orchid (Neottia nidus-avis), a short fawn-coloured saprophytic orchid which lacks chlorophyll and is semi-parasitic on some other plants.

Witch's Broom is a gall which occurs on a variety of trees, most often on Birch (Betula species) or on Hornbeam (Carpinus species) and various Conifers, but sometimes on Wild Cherry (Prunus avium). It is caused by an infestation from one of a number of different organisms including fungi, oomycetes, phytoplasmas, virii, insects, mites, nematodes and even by Mistletoe, but the most frequent cause is the ascomycete fungus Taphrina betulina. It starts off as green buds on the tree, which may remain as buds for several years until the buds grow into shortened branches, or slender shoots (twigs). In the spring, as in these photographs, small buds may sprout from these twigs before the trees leaves arrive, and either fall before the main leaves arrive, or themselves sprout into yet more twigs. It is of little consequence just causing abnormal twig proliferation and reduced flowering in the infected parts.

A CYTOKININ

Witch's Broom can also be caused by cytokinins, which are a class of phytohormones which promote cell growth by division (cytokinesis). There are several natural Cytokinins divided into two groups, the Adenine-type (such as Kinetin (originally discovered in Millet), Zeatin (first found in Zea Mays) and 6-benzylaminopurine (a synthetic cytokinin) and those based on phenylurea such as N-N'-DiPhenylUrea (found in coconut milk) and the synthetic Thidiazuron which is used extensively in tissue culture and rooting hormones.

Kinetin is present in Pearl Millet (Pennisetum glaucum) and appears to be produced in those specimens infected by Sclerospora graminicola which produces a callus. The kinetin is found within the callus. plant growth substances such as Kinetin are also produced in the roots of Pearl Millet suffering bacterial infection by Azospirillum brasilense, which is a nitrogen-fixing bacterium. This bacterium also produces other plant hormones such as Indole Acetic Acid and a smaller amount of Gibberelin.


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WITCH'S BROOM

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