Synchytrium taraxaci de Bary & Woronin   

Kingdom: Fungi
Phylum: Chytridiomycota
Order: Chytridiales

British distribution: Widespread and locally frequent.
World distribution: Europe, North America, probably elsewhere but some reports may refer to related species.

Synchytrium taraxaci lesions on Taraxacum leaf

A leaf pathogen of dandelions (Taraxacum officinale agg.), and reported on other members of the plant family Asteraceae (= Compositae). Susceptible plants can have highly distorted leaves and flowers and the whole plant lacks vigour. Casual observation on the University campus suggests that some dandelion microspecies, notably Taraxacum boekmanii, are heavily infected and have reduced survival, while adjacent plants of other microspecies show little or no infection.

Synchytrium taraxaci lesions on Taraxacum leaf, closer view

Blister-like sori are rust brown to red and can be confused with rust fungi on the same host. However, the sori consist of rounded-angular sporangia which release zoospores at maturity. Infection of new plants in a population can be rapid, sometimes with die-back of the plants concerned, though vigorous production of new leaves in early summer can outpace the damage caused by the fungus.

Synchytrium taraxaci: maturing sporangia.

Synchytrium taraxaci: sporangia after release of most of the zoospores.

Synchytrium is a genus of over 120 species of plant parasites, though most other chytrids (members of the phylum Chytridiomycota) are aquatic. Most well known is S. endobioticum, cause of Wart Disease in potatoes, though legislative controls and use of resistant potato cultivars mean that this disease is now rare here.

Most Synchytrium species are highly host-specific, though S. aureum is an exception – reported from numerous hosts in many different families. Widespread in Europe and elsewhere in the world, it is apparently rare in Britain, with just a few records in the British Mycological Society database. Other British species, listed and described by Ellis and Ellis (1997), are S. anemones on Wood Anemone (Anemone nemorosa), S. mercurialis on Dog's Mercury (Mercurialis perennis) and S. succisae on Devil's-bit Scabious (Succisa pratensis), cause of the reddish or purplish galls often seen on this plant.

Webster (1980) gives more details of S. taraxaci and a full account of the genus was given by Karling (1964).

Photographs: Paisley, Renfrewshire, April 2000.

•   Ellis, M.B., & Ellis, J.P., (1997). Microfungi on land plants, an identification handbook (2nd ed.). Richmond Publishing Co., Slough.
•   Karling, J.S., (1964). Synchytrium. Academic Press, New York.
•   Webster, J., (1980). Introduction to fungi (2nd ed.). Cambridge University Press, Cambridge.

© A.J. Silverside
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