Llanelli Naturalists Newsletter - No. 74 - July 2008
R. Nigel Stringer and Richard H. Davies

As many of you are aware, rust recording in Carmarthenshire started in 1995 and since then, thanks to the efforts of many Llanelli Naturalists members, a large database of records has been compiled.  This formed the basis of a rust database for the whole of Wales.  Since 1995 records have regularly been sent in from North Wales (Debbie Evans), Mid Wales and the Marches (Ray Woods, Tom Preece), West Wales (Arthur Chater) and South-east Wales (Graham Motley, Paul Smith) together with records from Carmarthenshire and West Glamorgan from Ian Morgan (IKM), RHD & RNS.

The total number of Welsh records now stands at 34,000 with ca. 2,500 predating 1995.  This has been a tremendous effort by all concerned as the British Mycological Society’s database (FRDBI) lists 37,000 rust records for the whole of the UK since 1880.  Three thousand Welsh records are included in the database.

Unfortunately, the momentum of rust recording has been curtailed over the last two years due to illness (RNS), but this has meant that time has been made available to collate and analyse some of the data collected to date.  Interesting trends are beginning to emerge both in relation to the recording side of the project but also in relation to the biology of some rust species.  The total number of rusts recorded for Britain is somewhere in the region of 282, with about 20 of these having been recorded on live imported foreign plant material or introductions. Interestingly, the total number of rusts recorded for Wales so far is 227 - which is a high percentage of the UK total.

As with all species groups, the intensity of recording is biased geographically around the home bases of the specialists.  It will therefore come as no surprise to know that the highest number of rust records has been recorded for Carmarthenshire (26,000) and the lowest for Flintshire (129). Another major factor that determines whether a particular rust will be present is obviously the availability of the host plant as all rusts are parasitic.  To complicate matters further, some rusts have a complex life cycle that involves the production of different spore stages on two completely unrelated host plants. The two host plants must be present and growing close to each other to allow cross infection or the rust will be unable to survive.

Puccinia  sessilis rust infecting Arum maculatum (Lords and Ladies). Photo: R.N. StringerA local example of such a rust is Puccinia sessilis which infects Arum maculatum (Lords and Ladies) in the spring and Phalaris arundinacea (Reed Canary-grass) later in the year.  A. maculatum is a very common plant of damp, base-rich woodlands and hedgerows of the county but very few Arum plants are infected.  This is because the alternate host (Phalaris arundinacea) is absent or does not grow in close proximity to Arum at these locations.  The best site in the county to see the rust is at Pant-y-llyn turlough, Carmel where both plants grow in profusion in very close proximity to each other.  The rust infection on Arum is so severe that the whole of the underside of the leaf is coloured orange due to the large number of sporulating bodies produced by the rust.

In 1996 the authors studied these infection patterns on Arum in greater detail. Arum exhibits a phenomenon known as morphism with regards its leaves. Some plants have all their leaves distinctly marked with black spots, whilst other plants have no spots at all.  Early botanists recognised these two forms as distinct species.  Up until now no one has been able to explain in terms of evolution what the selective advantage is between spotted and non-spotted leaves.  The authors carried out a survey counting the number of “infection blotches” of rusts on spotted and non-spotted leaves of Arum at Carmel.  A large number of leaves were sampled during the survey and the results analysed statistically. It was observed that plants with spotted leaves had significantly less “rust blotches” than plants with non-spotted leaves.  So is this the reason why Arum exhibits this phenomenon – spotted leaved plants are more resistant to rust disease?  It is noticeable that plants with spotted leaves seem to be more abundant only where Phalaris is growing close by and that most of the Arum in the county is of the non-spotted morphotype.  

A strategy used by rusts to overcome this dependency on two hosts is the obvious one – do away with one of the hosts!  This happens with the rusts that occur on Rosa (rose) and Rubus (blackberry) but they still retain all their spore stages in the life cycle.  I am sure that many members will have seen the wine-red blotches on the upper surface of blackberry leaves in summer and autumn.  Turn these leaves over and you will see either orange spore mass pustules or violet-black spore mounds of the rust Phragmidium violacaceum – one of our commonest rusts.  The different coloured spore masses indicate two different spore types produced by the rust.  The orange mass consists of spores which spread the disease rapidly and the violet-black spores are the “overwintering” spores – the functional equivalent of seeds. 

As you have probably realised, rusts tend to be host specific.  Some have a “wider” host range than others.  For example Puccinia malvacearum - the rust on mallow is found on a wide range of species within that family.  Other rusts e.g. Puccinia veronicae is only found on Veronica montana (Wood Speedwell) and no other member of the family.  Thus, the distribution and abundance of the host has a bearing on how “common” or “rare” a particular rust is.

One of the rarest of our Welsh rusts is Puccinia scorzonerae which infects Scorzonera humilis (Viper’s grass), a plant confined to one site in Dorset before it was discovered on an SSSI in Glamorgan by Julian Woodman of CCW in the mid 1990s.  The specimen was sent to RNS as it had “blotches” on the leaves.  These “blotches” were the spore bodies of the rust which had never been previously recorded in Britain.  The rust was confirmed by scientists at Kew who out of interest went through their Higher Plant herbarium specimens and discovered the same rust on a specimen of Viper’s grass collected in the 19th. Century!

Another important discovery was made by Debbie Evans in North Wales during 2006 when she found a rust on Oxyria digyna (Mountain Sorrel). The rust, Puccinia oxyriae has only been recorded on a total of five occasions in Britain, being last recorded in 1941, and until 2006 was thought to be extinct. 

However, not all rusts are so rare.  Fern rusts are very common in the county even though records throughout the UK are sparse.  The rusts on most of our ferns are not “rusty” in colour at all. They appear as white blobs on the underside of the frond – the white colouration being due to the extruded spore contents being colourless unlike most rusts whose spore contents are pigmented orange.  Milesina kreigeriana is the rust found on Dryopteris dilatata (Broad Buckler-fern) and is extremely common throughout the county, as is Milesina scolopendrii found on Phyllitis scolopendrium (Hart’s-tongue) which also produces these characteristic white spore masses on the underside of decaying fronds.

Seasonality or the appearance times of the rust spore bodies on different hosts can also vary which is why rusts can be found at all times of the year, unlike the fruiting patterns of other fungi such as the Agarics which tend to be biased towards the autumn.

Milesina  kreigeriana infecting senescent leaves of Dryopteris  dilatata (Broad Buckler-fern). Photo: R.N. StringerThe seasonality of rusts does depend on the growth patterns of the host i.e. when it emerges and the duration of the growing season. Fern fronds are present all the year round and Milesina dieteliana, the rust on Polypodium (Polypody) can be found more or less at any time of the year. The young fronds are produced from early summer onwards with senescent fronds most abundant in winter and spring which is the peak time when the rust is most prominent.

This contrasts markedly with Puccinia adoxae which is one of two rusts commonly found on Adoxa moschatellina (Moschatel).  This rust has only one spore stage and its appearance ties in with the short season of the host which emerges in early spring and dies back within a few weeks.  So changes in patterns of appearance of the spore stages of different rusts very much depends on the biology of the hosts.

Seasonality in the appearance of rusts on Polypodium (polypody) and Adoxa (Moschatel).We are also subject to the arrival of “new” rusts to our shores.  One of these – the rust on Bellis (daisy) was recorded for the first time in the UK in 1997 and has been the subject of much debate between scientists across the Atlantic for many years as experts couldn’t agree on its identity because of its similarity to other species.  The matter was partly resolved after work done initially by Dr. Tom Preece in Shropshire followed up by laboratory studies carried out in the University of Exeter.  It turned out that this rust, Puccinia distincta, originated from Australia and is now widespread across the whole of the UK affecting native and cultivated forms of daisy. The rust is very characteristic and produces prominent bright orange spore bodies on leaves, which as a result of infection tend to be more upright than flattened in a normal rosette habit.  In 1995 and 1996 this rust completely devastated and killed off a large proportion of the daisy population at Peoples’ Park, Llanelli and much of the coastal hinterland between Bynea and Pwll.

A very recent new arrival is Melampsora hiratsukanum which occurs on Alnus (alder).  This rust was first described from Japan in 1927 and is now well established across Europe, having arrived in Estonia in 1996, Finland in 1997 and Norway in 2001.  Professor Halvor Gjaerum of Norway alerted us to the presence of this rust as we had thought that the rust on Alder was the same rust as that more commonly found on Betula (birch): Melampsoridium betulinum. Herbarium specimens were rechecked and we were able to confirm that some of our earlier determinations were incorrect and the rust was in fact M. hiratsukanum.  This revision meant that the first sighting of this rust in Wales occurred in October 2000 by IKM and RNS from Cynheidre.  Interestingly, this rust favours Alnus incana (Grey Alder) even though it is present on other Alnus species.  In 2006 RHD reported that the coastal fringe of alder seaward of the Burry Port Coast Road was severely impacted by this rust from as early as July that year.

Recently Alan Orange of the National Museum of Wales, Cardiff, sent away a leaf of Alnus infected with M. hiratsukanum for DNA analysis.  The rust matched the microscopic description of M. hiratsukanum but the DNA analysis indicated that it matched the DNA sequence of the birch rust M. betulinum!  Clearly the two rusts are very closely related but we are not sure if the leaf that was sent had been unknowingly infected by both rust species.

Another new rust to appear on our shores is one which Arthur Chater recorded infecting Solidago virgaurea (Golden-rod) growing in Ceredigion in 2003.  This rust, Uromyces sommerfeltii, is a European species with centres of population in Austria, Switzerland and all Scandinavia.

Puccinia  buxi parasitic on Buxus spp. (box).  Photo: R.N. StringerWhilst there is no evidence that there have been extinctions of rusts from our shores, it seems that some of our rusts may be changing.  The rust Puccinia buxi is parasitic on Buxus spp. (box).  Dr Tom Preece has studied this rust for over forty years and his research has shown that rust infections are associated with “veteran” box trees.  He found that box trees growing in old established gardens, cemeteries, parklands and historic sites (castles, abbeys etc.) were nearly always infected but that young plants sold in garden centres or established in “modern or recent” gardens were not.  The reasons why the young box plants are not susceptible remain a mystery: is the rust loosing its capacity to infect or is the host plant becoming more resistant?  Are environmental factors the cause of this strange phenomenon?  Box rust is fairly common throughout Carmarthenshire in churchyards, Dinefwr Park and Castle grounds and old hedgerows in the Cilycwm-Rhandirmwyn area.  Numerous visits to garden centres and the National Botanic Garden of Wales at Middleton support Dr Preece’s findings as no young infected box plants have yet been found.  It again would be very interesting to hear from any Llanelli Naturalists members if they come across any rust infections on young box plants.                              

The rust project has been going for 12 years and during this time we have contributed towards a better understanding on the distribution of rusts not only in the county but the whole of Wales. Data is still being analysed and another interesting trend that seems to be emerging is that with some rusts, especially those found on grasses the season seems to be extending later into the year.

This trend has recently been shown for other fungi – mainly litter decomposing forms where the fruiting period of some species of Agarics has, over the last four decades extended gradually further into the autumn period due to milder weather and the lack of early and severe frosts.

All the rust work to date would not have been possible without the efforts of all those people mentioned in the article, not only because of their collections of rust specimens and records but because of their ability to identify the host plant accurately which is so important in relation to rust identification. Special mention however must go to Dr Tom Preece for his commitment and support of the project and advice to the authors on a weekly basis since the project began.