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Microfungus on Garden Pansy

Posted: Tue Nov 21, 2017 12:16 pm
by Simon Horsnall
Can anybody enlighten me on what is causing the spotting on my Garden Pansy, Viola X wittrockiana leaves. I am assuming it is a hyphomycete. Apologies if this should have gone in the plant diseases forum, not quite sure what the protocol is with these.

Location: Ilkeston,VC57
Date: 21/xi/2017
Pale brown, dark-bordered spots becoming zonate with age
Colonies fasciculate, hypophyllous
Conidia hyaline 17 - 25 X 4.5 - 5 microns. At 600X and with careful tweaking of the light, some septa appeared to be present although I could not be absolutely certain how many

Photos of leaf upperside, close up of colonies and micrograph of conidia

Using Ellis and Ellis, I cannot find anything which matches the combination of characters so I've probably done something stupid.
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Re: Microfungus on Garden Pansy

Posted: Tue Nov 21, 2017 1:42 pm
by Chris Yeates
Hello Simon

Of course you have done nothing stupid; this is a well-presented query. Ellis and Ellis, while excellent, is not complete and there has been a lot of work on these fungi since that book was published. Your fungus is Ramularia agrestis Sacc. I have double checked in Uwe Braun's monumental A Monograph of Cercosporella, Ramularia and Allied Genera, Vol. 2 and the only other taxon associated with Viola x wittrockiana is a var. deflectens (Bres.) U. Braun of the same species.
As far as I can see the chief difference between the latter and the nominal var. agrestis is that it can have up to 4 septa - var. agrestis has 0-1(2) septa. Most stains should clarify the matter.
If you look at the relevant page in Index Fungorum:
Ramagr.jpg
You can see that while both varieties are listed there (IF is a nomenclatural database); it points both to the parent species in Species Fungorum (green text) which is a taxonomic database. For years now this has been the case with virtually every infra-specific taxon. I still cannot understand why Paul Kirk (who is usually a very sensible guy, and a fellow Yorkshireman to boot) does this. Sub-species, varieties et al. can be particularly important categories when dealing with plant pathogens - Mycobank keeps them separate. The "paper-trail" is important with any biological record - what the original recorder called it (even if they were mistaken) should not be lost. Sorry, but this is one of my personal bugbears.

best wishes
Chris

Re: Microfungus on Garden Pansy

Posted: Tue Nov 21, 2017 2:44 pm
by Simon Horsnall
Many thanks Chris for such a swift, informative and comprehensive reply.

Ellis and Ellis describe R. agrestis as amphigenous and that was where I had ruled it out so yes, something stupid. Next time I shall use that to inform but not eliminate my selection.

I wholeheartedly agree with your sentiments on naming.

I shall try staining the tissues and see if I can determine the number of septa.

Re: Microfungus on Garden Pansy

Posted: Wed Nov 22, 2017 10:50 am
by Simon Horsnall
Update

After staining in Congo Red, there appears to be 0 - 2 septa (2 being exceptional) in the spores therefore I think we can safely conclude Ramularia agrestis var. agrestis Many thanks once again.