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BIODIVERSITY REFERENCE
 
   Microbotryum lychnidis-dioicae (Liro) G.Deml & Oberw. (agg.)   
(includes M. silenes-dioicae T. Giraud, Denchev & M.E. Hood)
 
(Microbotryum violaceum complex)


Kingdom: Fungi
Phylum: Basidiomycota
Subphylum: Pucciniomycotina
Class: Microbotryomycetes


British distribution: Widespread, and generally common, but most records made as "Ustilago violacea".
World distribution: Europe, N. America, no doubt elsewhere.


When writing this page, I considered the recently described M. silenes-dioicae to be an incompletely host- and genetically-separated variant best treated as a synonym of M. lychnidis-dioicae (see discussion below). Since then it has been given separate recognition in the FRDBI, with all records on Silene dioica arbitrarily assigned to it without any DNA confirmation. I am not, for the moment, changing the present text (nor my opinion), my intention being to add a photograph of parasitised Silene latifolia when/if opportunity permits.


Microbotryum lychnidis-dioicae is the familiar anther-smut on White Campion (Silene latifolia) and on Red Campion (S. dioica). In Europe it occurs too on the closely related Night-flowering Catchfly (Silene noctiflora) (Vánky, 1994), but S. noctiflora, an annual, arable weed species, is now rare in Britain and there seem to be no British records on this host.

M. lychnidis-dioicae is part of the Microbotryum violaceum complex (q.v.) of species that parasitise members of the Pink Family (Caryophyllaceae). These were formerly believed to be true smuts (Ustilagionomycetes) and were included in the large genus Ustilago (as U. violacea). However, far from being 'text-book' smuts, the campion smuts are actually allied to the rust fungi (Pucciniomycetes), and molecular evidence supports the recognition of M. lychnidis-dioicae as separate from M. violaceum.


Microbotryum lychnidis-dioicae in anthers of Red Campion
Microbotryum lychnidis-dioicae in anthers of Red Campion
Microbotryum lychnidis-dioicae in anthers of Red Campion, close view
Microbotryum lychnidis-dioicae in anthers of Red Campion, close view
Microbotryum lychnidis-dioicae in anthers of Red Campion (Silene dioica), Chatelherault, Lanarkshire, June 2010.


As in the case of the true anther smuts, the fungus completely takes over the anthers of the host, which burst open to release the purple, powdery spores instead of pollen. Infected flowers have been recorded as lasting considerably longer han uninfected flowers, the fungus also inducing strengthening of the flower-base and filaments of the stamens (Uchida et al., 2003). It is noticable in the photographs above that while some flowers are crumpled with age, the centre part and infected stamens remain in good condition.

Remarkable about this species is that it is able to over-ride sex determination in the host plant. Both S. dioica and S. latifolia are dioecious, populations containing separate male and female plants, but M. lychnidis-dioicae causes anther-development in the female host-plants.

Uchida et al. (op. cit.) provide an excellent, illustrated summary of the development of anthers in both male and female plants. Sex expression in these Silene species is determined by an X-Y chromosome system, as in higher animals, XX coding for female and XY coding for male, the Y-chromosome being morphologically distinguishable. The Y-chromosome appears to carry genes that suppress female development, and in infected XX plants the fungus evidently partially substitutes for the Y-chromosome genes absent in female plants. It can be seen in the photographs in their paper that this replacement of female characters by male is not complete; female plants retain their characteristically different calyx shape and characters.


Microbotryum lychnidis-dioicae in anthers of Red Campion, teliospores
Microbotryum lychnidis-dioicae, teliospores from anthers of Red Campion (Silene dioica), Chatelherault, Lanarkshire, June 2010.


Identification
On current knowledge, simplest identification of M. lychnidis-dioicae is by identification of the host plant. Molecular studies, e.g. by Kemler et al. (2006), provide support for accepting several host-restricted species within the M. violaceum complex, including M. lychnidis-dioicae. Current British taxonomic treatment (see Legon et al., 2005; Spooner & Legon, 2006) is to adopt a species-concept that equates with that of Kemler and his co-workers, and a restricted circumscription of M. violaceum itself. This is discussed more fully on the M. violaceum page. To date, considerable molecular work has not detected any further Microbotryum species on Silene dioica or S. latifolia, except as discussed below.

Morphologically, M. lychnidis-dioicae is little differentiated from closely related taxa. The spore surfaces carry a high, reticulate mesh (see photo above) and according to Vánky (1994, 1998, 2004), based on previous work by Scholz and Scholz, the meshes are irregularly polygonal and up to 1.4 µm in diameter, whereas the meshes are smaller and/or more rounded to regularly polygonal in M. violaceum, sensu stricto, and in other taxa of the complex. Vánky himself (2004) considers these differences to be small and variable.

There is now a very substantial body of scientific literature comparing strains on different host species, using molecular techniques to demonstrate further genetic differentiation and isolation (see, e.g. Le Gac et al., 2007; Devier et al., 2010), and a number of such strains within the M. violaceum complex have also been given names as species, adopting a very narrow species-concept. Genetic differences are small in comparison with those accepted by Kemler et al., and if certain of these additional taxa are worth recognition in formal taxonomy, they would seem better treated as infra-specific variants. One such entity is M. silenes-dioicae, based on the strain on Silene dioica, whereas M. lychnidis-dioicae is treated, despite its name, as the strain on S. latifolia. [I presume the typification of M. lychnidis-dioicae was considered.] However, apart from the close molecular relationship of these two taxa, Biere & Honders (1996) showed that cross transmission of strains between S. latifolia and S. dioica in either direction is possible (though much more readily from S. latifolia to S. dioica), and also to hybrids between the host species. Gene flow between strains on the two host plants is evidently limited, but overall it seems best to consider M. silenes-dioicae as a synonym of M. lychnidis-dioicae. Outside specialist laboratories, no other taxonomy is practical.


References
•   Biere, A., & Honders, S., (1996), Host adaptation in the anther smut fungus Ustilago violacea (Microbotryum violaceum): infection success, spore production and alteration of floral traits on two host species and their F1-hybrid. Oecologia 107: 307–320.
•   Devier, B., Aguileta, G., Hood, M.E., & Giraud, T., (2010), Using phylogonies of pheromone receptor genes in the Microbotryum violaceum species complex to investigate possible speciation by hybridization. Mycologia 10: 689–696.
•   Kemler, M., Göker, M., Oberwinkler, F., & Begerow, D., (2006), Implications of molecular characters for the phylogeny of the Microbotryaceae (Basidiomycota: Urendiniomycetes). BMC Evolutionary Biology 6 (35). [Available online: http://www.biomedcentral.com/1471-2148/6/35].
•   Le Gac, M., Hood, M.E., Fournier, E., & Giraud, T., (2007), Phylogenetic evidence of host-specific cryptic species in the anther smut fungus. Evolution 61: 15–26.
•   Legon, N.W., Henrici, A., Roberts, P.J., Spooner, B.M., & Watling, R., (2005), Checklist of the British and Irish Basidiomycota, Royal Botanic Gardens, Kew.
•   Spooner, B.M., & Legon, N.W., (2006), Additions and amendments to the list of British smut fungi. Mycologist 20: 90–96.
•   Uchida, W., Matsunaga, S., Sugiyama, R., Kazama, Y., & Kawano, S., (2003), Morphological development of anthers induced by the dimorphic smut fungus Microbotryum violaceum in female flowers of the dioecious plant Silene latifolia. Planta 218: 240–248.
•   Vánky, K., (1994), European smut fungi, Gustav Fischer Verlag, Stuttgart.
•   Vánky, K, (1998), The genus Microbotryum (smut fungi). Mycotaxon 67: 33-60.
•   Vánky, K, (2004), Anther smuts of Caryophyllaceae. Taxonomy, nomenclature, problems in species delimitation. Mycologia Balcanica 1: 189-191.



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