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A novel host for Discostroma tostum
Chris Yeates, 08-07-2020 16:47
Chris Yeates
Bonjour tous

While searching for the downy mildew Peronospora arthurii on Oenothera glazioviana I noticed black spots on the dead standing stems of the previous year. The host is not native to the UK, being widely naturalised from its garden origins. Here it was growing in a fairly rich grass/herb community on the site of former 19th century buildings.

The perithecia were frequent along much of the length of the dead stems, from 5mm to 10mm stem-width. In many cases they had become exposed by erosion of the outer fibrous cortex. On examination under the microscope, there was abundant material in good condidtion. Looking at the spores my first impression was that I was facing one of the puzzling Didymella species; however the asci were clearly unitunicate. In addition there appeared to be an apical apparatus, this was confirmed by a strong blue reaction in Baral'sche Lösung. Although my spore measurements were slightly larger (11.6-13.8 x 5-5.6µm) than those usually given - closest to those in Brockmann (1976) - I was strongly reminded of Discostroma tostum. Associated with the perithecia were occasional distinctive conidia of a Seimatosporium - see images; looking at Brockmann's paper on Discostroma in Sydowia,28, pp. 275-338 there were the same conidia - again, see attached image.

So I am confident that this is Discostroma tostum, a common species on stems of Chamerion and Epilobium, but not associated with Oenothera. An online search has only come up with a single possible incidence: https://www.discoverlife.org/mp/20l?id=BPI611108 (unfortunately the hyperlink under "More details" doesn't seem to work). The jump from Epilobium to Oenothera does not seem too unusual, as molecular work has shown the two genera to be monophyletic.


I would be interested to know if anyone else has come across this fungus on any hosts other than Epilobium, and would encourage people to have a look at Oenothera in their areas. One thing that has arisen from this exercise is that the illustrations in Dennis (1981) and Ellis & Ellis (1985) are rather poor - I suspect this is due to "fungarium mycology" rather than vital mycology and this has contributed to the disparity in spore measurements. Although I have used the name Discostroma tostum, there is a strong case, under the "one fungus, one name" criterion, for its being called Seimatosporium tostum (Berk. & Broome) Rossman & W.C. Allen - see Rossman et al. in IMA Fungus, 7, (2016) p.5.


Cordialement


Chris

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Viktorie Halasu, 08-07-2020 22:03
Viktorie Halasu
Re : A novel host for Discostroma tostum
Dear Chris,

the link to BPI works now, it lists D. Hruby's 1928 collection from Rottigeltal near Krumau in Moravia (with current names: the valley of Rokytna river near Moravsky Krumlov). "D. Hruby" might be an error in first name, as Johann Hruby published in 1928 a collection od Paradidymella tosta on Oenothera biennis from near a large viaduct near Eibenschitz (= Ivancice). Rokytna river actually connects these two towns, so it might be the same locality. "Didymella torta" (typographic error?) is also listed in Hruby (1928): Die Pilze Mährens und Schlesiens. Hedwigia 68, but without locality or host.


A Paradidymella tosta specimen was also distributed in Reliquiae petrakianae no. 77, C. Scheuer wrote that BPI got the first five complete fascicles (and fasc. 6-14 partially). Perhaps that's the specimen on BPI website? edit: but the specimen held in CUP has Epilobium as host (https://mycoportal.org/cup/mycology/RelPetrak0/Rel.Petrak.0077.jpg).


Best regards,
Viktorie


Johann Hruby (1928): Die pflanzengeographischen Verhältnisse Westmährens. – Verhandlungen des naturforschenden Vereines in Brünn – 62: 30 - 77. https://www.zobodat.at/pdf/Verh-naturf-Ver-Bruenn_62_0030-0077.pdf


Christian Scheuer (1992): Reliquiae Petrakianae - Alphabetisches Gesamtverzeichnis und Corrigenda (Cumulative Index and Corrigenda).

Chris Yeates, 10-07-2020 16:35
Chris Yeates
Re : A novel host for Discostroma tostum
Many thanks for your detective work Viktorie - very useful information.

Something I forgot to point out in the initial post is that Chamerion angustifolium (a usual host for this fungus) was close by - the pink spikes of that plant can be seen in the background of the first photograph.

Best wishes

Chris