Dear David,
1) As far as I know, all decay fungi have the capacity to grow in pure
culture in the absence of a living host. If so, the term "biotrophic", in the
strict sense, cannot be applied to any decay fungus.
1) They have the capacity to grow (hyphae, mycelia), but do the obligate
(biotrophic) parasitic species also fruit with "normal" and fertile
fruitbodies from dead wood under in vitro and controlled conditions ?
A. Some decay fungi can grow only on dead wood, probably because they require
better aeration than occurs in living trees. I regard these fungi simply as
saprotrophs.
B. Other decay fungi can grow in living trees but only in wood that is
already dead. This wood could be dead because of physical injury (e.g. a
pruning wound) or because of the dieback of part of the tree. On the other
hand, the wood could be dead because it has become heartwood or ripewood as a
result of aging. I regard these fungi also as saprotophs, but perhaps they
deserve to be given a new description to denote the fact that their tolerance
of poor aeration enables them to grow in the dead wood of living trees.
C. Yet other decay fungi have the capacity to colonise previously undamaged
sapwood. Zones of sapwood die as a result of this fungal colonisation. In
some cases, the entire tree dies. I think that these fungi could be regarded
as necrotrophic parasites, but I think that this categorisation is open to
debate.
A/B/C : your definition of necrotrophic parasitic and saprotrophic species
implicates, that almost all of the Dutch, German and Scandinavian literature
on wood degrading macrofungi has to be rewritten or reviewed, because almost
all the species now listed as necrotrophic parasitic would by your definition
be saprotrophs.
2) I have circumstantial evidence that Meripilus giganteus, for example, is
sensitive to oxidation, although it often survives for years in dead roots.
2) I have circumstantial evidence of M. giganteus fruiting from still living
roots, because I have seen it been surrounded by ectomycorrhizal macrofungi
(mostly generalistic Russula species such as R. ochroleuca and/or R.
parazurea and Laccaria laccata s.l.) fruiting from remaining living tissues
of the (beech) roots they had colonised before and/or (again) after the tree
was felled and removed while leaving only major and secondary/adventitious
roots behind.
3) The fungus might potentially be able to continue using the remaining wood
as its energy source. In reality, however, it is replaced by other organisms,
which are better able to tolerate the altered conditions. (For example, I
recall some Japanese research on the failure of commercially cultivated
Shi-itake mushrooms to develop in logs. The reason was that the logs were
slightly too dry; not enough to kill the Shi-itake fungus, but enough to
allow the fungus to be replaced by latently-established fungi (Ascomycetes).
3) I just finished reading an article by Thom Kuyper (Coolia, 55-1, 2012)
reviewing recent publications on the effectiveness of saprotrophic wood
degrading macrofungi in decomposing wood when they arrive first and stay
alone for a while or decomposing wood in interaction with other also from the
start or later on present saprotrophic species. Apart from some species being
more effective than others, he concludes, that - especially for white rotters
- the effectiveness is fastest and far more optimal if a species arrives
first and stays "single" for some time, as opposed to competing species
investing in the defense of individual territories causing less and slower
decomposition of the wood and states, that the present concept of succession
of wood degrading macrofungi should be thoroughly reviewed.
4) Inonotus hispidus: this could be regarded as a necrotrophic parasite,
since it can grow through reaction zones [by tunnelling through the cell
walls (=soft rot)] into previously living sapwood. It is not biotrophic (in
the strict sense), since it can grow on dead wood and on artificial media in
pure culture (which means no competition from other fungi etc.).
4) See 1).
5) There is a suggestion that there are different strains of M. giganteus,
some of which are more able than others to grow into sapwood and thus
continue to survive. If there is still plenty of wood available in the roots
of a dead beech tree, M. giganteus can continue growing and fruiting for
several years. I have even seen it fruiting in city streets, long after the
removal of its host tree.
5) See 2). And as until now no one has checked M. giganteus systematicaly for
not being its American look-a-like Meripilus sumstinei, I would not be
surprised if one or more strains would turn out to be another species than M.
giganteus.
6) Phellinus tremulae. You have mentioned another interesting concept here,
by referring to this fungus as a primary parasite in aspen. According to the
late Alex Shigo and his co-worker Walter Shortle, there are various decay
fungi develop only in succession to a range of other (non-decay) organisms
that are primary colonisers of wounds. Other fungi are, I think, clearly able
to act as primary colonisers, and I think that this is probably true of P.
tremulae in aspen. Also, the idea of succession probably needs to be
re-appraised
6) I totally agree, see 3).
7) Pholiota squarrosa: In my experience, this fungus can cause very extensive
hollowing in various host species (but with adaptive growth that usually
prevents mechanical failure). A very extensive decay column might indicate
that this fungus can extend into previously living sapwood, in which case it
could be called a necrotrophic parasite.
7) IME, tree species with superficial root plates (Platanus), tree species
unable of regenerating major roots, that died after heavily pruining
(Platanus, Robinia) and/or tree species with easily decomposed heartwood
(Populus, Salix) are most vulnerable for windthrow after an infection with P.
squarrosa, where as beech seems to be rather unaffected by an infection of
the trunk's base. And did you ever document it fruiting from dead wood alone ?
Regards,
Gerrit
Without wanting to complicate things any further, some citations on
biotrophic and necrotrophic parasitic macrofungi from Scandinavian and Dutch
literature and my own experience, I would like to have your opinion on,
follow.
- The (biotrophic) parasitic Inonotus hispidus, that grows "on living
hardwoods" and "dies with the tree" (my words), "is capable of killing
sapwood (soft rot) in living trees" (Ryvarden & Gilbertson, European
Polypores I).
- In my experience, the same thing applies to Inonotus cuticularis on Fagus
and to Meripilus giganteus on Fagus and the 16 other tree species it is
this far documented from, of which the mycelia of both species also invade
and cause a soft rot of living tissues.
- The (biotrophic) parasitic Phellinus tremulae "spreads in the inner
sapwood and inner wood of living trees in the absence of other organisms,
indicating that it is a primairy parasite in aspen" (Wickström in :
Ryvarden & Gilbertson, European Polypores II).
- And is Pholiota squarrosa obligate (biotrophic) parasitic or - according
to Arnolds, et al. : Overzicht van de Paddestoelen in Nederland -
necrotrophic parasitic, as it dies with the tree and never fruits from dead
wood alone, which is very exceptional for parasitic Agaricales ?
So how would you label these macrofungi, as obligate (biotrophic) parasitic
or necrotrophic parasitic ?
Regards,
Gerrit
biotroof - food withdrawing to live parts of a host.
I think that this simply means that the parasite is obtaining its food from
living tissues. This is okay as a literal translation of the original
Greek: "bios" = life / "trophe" = food. I do not, however, think that this
definition is precise enough to distinguish between a biotroph and a
necrotroph (just as you implied in your previous message).
In Ainsworth and Bisby's Dictionary of the Fungi (8th edition, CAB
International), the definition of biotroph is as follows:
"Biotroph: an obligate parasite growing on another organism, in intimate
association with its cytoplasm."
I think that the Ainsworth & Bisby definition means almost the same as the
one that I wrote yesterday. I did not, however, use the word "obligate"
(meaning that the parasite can grow only on the living host; not on a
non-living culture medium), because I am aware of a few rust fungi (for
example) that have been grown on artificial media, with great skill and
difficulty. On the other hand, it is quite useful to use the word
'obligate', since this clearly shows that wood decay fungi cannot be
biotrophic according to the strict definition. They must either be
necrotrophic parasites (if they invade and kill living tissues) or
saprotrophs (if they grow only in tissues that are already dead).
I use the definitions from this list (in Dutch) (
www.springerlink.com/content/tuj653216XXXXXXX ) and to add some more
information on the subject of tree species specific strategies of parasitic
macrofungi being part of and co-evolved within a tree species specific
ecosystem (Keizer, 2007/2011), the following on the tree species colonised
by Fomitopsis pinicola on the European continent.
I hadn't realised the use of "biotrophic" and "necrotrophic" were different
in the UK and on the continent; thanks for mentioning this.
I don't know whether other UKTC members share my unease about identifying
species of Ganoderma in the field. I would feel happier if each species
could be shown to have a distinct combination of characteristics (including
hyphal structure, average spore-size, DNA-based criteria, thickness and
hardness of the crust and the presence/absence of insect-galls). Perhaps we
are wrong in the UK to be identifying a large proportion of the Ganoderma
on beech as G. australe/adspersum. Various fungi do, however, show
genuinely different frequencies of occurrence between the UK and parts of
the near continent. For example, we seem to have more G. pfeifferi here.
Also, Fomes fomentarius is much less frequent on beech (and on other tree
species) in southern Britain than on the continent. It is more common in
northern Britain, where the main host is birch.
-----Original Message-----
From: Viper Snake [mailto:snake24@xxxxx.nl]
Sent: 21 December 2011 19:33
To: UK Tree Care
Subject: RE: Ganoderma applanatum/australe on n.maple - implications
Dear David,
Although there is quite a difference in your definition of biotrophic
and necrotrophic parasites and the definition of both terms on the
continent, as is included in all Dutch, German and Scandinavian
literature I refer to, I consider your definition to be the more
precise.
And after always microscopically assessing what perennial species of
Ganoderma I found on beech in The Netherlands and Germany, I have come
to the conclusion, that about 95 % of perennial Ganoderma species on
beech is G. lipsiense, followed by the rare G. pfeifferi and the
extremely rare G. australe.
Regards,
Gerrit
From: d.lonsdale2@xxxxxxxxxxx.com
To: uktc@xxxxxx.tree-care.info
Subject: RE: Ganoderma applanatum/australe on n.maple - implications
Date: Wed, 21 Dec 2011 18:29:51 +0000
Dear Gerrit,
In answer to your question, I define the relevant terms as follows:
1. Biotrophic parasite: a parasite which obtains its nutrients from
the living cells of the host (usually by the penetration of those
cells, without killing them). Examples include rusts and mildews.
2. Necrotrophic parasite: a parasite which obtains its nutrients by
killing cells of the host (usually by the secretion of enzymes and/or
toxins). These parasites are usually able to grow also as saprotrophs
(4, below) and they are therefore often alternatively called
"facultative parasites". Examples include many fungi and bacteria
that cause general dieback and/or decay of host tissue.
3. Hemibiotrophic parasite: a parasite which obtains its nutrients
both as a biotroph (usually when it first penetrates host tissue) and
as a nectroph (usually at a later stage, after an initial biotrophic
phase). Examples include many organisms that cause leaf spot diseases.
4. Saprotroph: an organism which obtains its nutrients from the dead
remains of one or more living organisms.
As far as I know, there are no wood decay fungi in categories (1) or
(3) above. Some of them have the ability to grow into previously
living sapwood, causing it to die (or become "dysfunctional" and then
causing decay. I think that they can be regarded as necrotrophic
parasites (2), but I do not like to use this term without
qualification, since many of them live predominantly on wood that is
already dead. This could be sapwood that has been damaged by injury,
or it could be central wood or the tree, which has become heartwood
or ripewood because of aging.
Traditionally, wood decay fungi have been described as "parasitic" if
they are found on living stems, branches or roots. I do not think
that this is correct if the fungus concerned is colonising only wood
that is already dead.
According to the above definitions, Ganoderma applanatum has been
observed to be mostly saprotrophic, whereas G. adpsersum/australe has
some capacity to act as a necrotrophic parasite. These observation
seem to be confirmed by some experimental work by my friends Schwarze
& Ferner at the University of Freiburg i. Br., Germany. (see:
http://www.enspec.com/articles/ENSPEC%20Research%20Paper%20-%20Ganoderma%20on%20Trees.pdf
)
Schwarze & Ferner found that G. adpsersum/australe was able to
penetrate defensive barriers (reaction zones), thus growing into
functional sapwood. It does not necessarily harm the tree seriously.
Instead, it might be able to co-exist with the tree for many years,
instead of dying out when it has utilised all the wood that was
initially available to it. In some cases, however, the fungus does
enough damage to the sapwood (especially in the roots of the tree) to
cause the decline and perhaps death of the tree. Also, the decay can,
in my experience, become overwhelmingly rapid if the wood becomes
more aerated because of excessive pruning or the storm-breakage of
major branches.
As suggested in the recent correspondence, G. adpsersum/australe
appears to behave differently in different host species. I think that
it can be especially aggressive in species with which it has not
co-evolved. I have seen examples where G. adspsersum/australe (or
perhaps a similar-looking species of Ganoderma) seems to have killed
exotic conifers such as Araucaria araucana. I agree that it can cause
extensive decay in the broadleaved trees in your list. However, in
Fagus sylvatica (one of its main hosts in the UK), the tree and the
fungus often seem to co-exist for many years. The co-existence is
probably even longer in species like Quercus robur and Q. petraea,
which have durable heartwood and therefore tend to become decayed
more slowly.
Regards,
David
-----Original Message-----
From: Viper Snake [mailto:snake24@xxxxx.nl]
Sent: 21 December 2011 14:14
To: UK Tree Care
Subject: RE: Ganoderma applanatum/australe on n.maple - implications
David,
1). Tony Croft has been using the term 'biotrophic parasite' in
relation to G. adspersum/australe on here. I questioned him about
these labels and asked him whether he could point me to any research
that demonstrated that the fungus was 'biotrophic' and/or
'parasitic', because this was news to me, but he hasn't replied yet.
Can you point me in the right direction?
1). Tony uses my terms and the results of my in situ research on
biotrophic and/or necrotrophic parasites, which I already have
explained on Arbtalk, see : 2.
http://arbtalk.co.uk/forum/529703-post53.html .
2). Similarly, that G. adspersum/australe is deterministically fatal
to Acers, no matter the circumstances, is also news to me. Where does
the research for this conclusion come from ?
2). From my own field research on the effects on the stability and
condition of different deciduous tree species of the biotrophic
parasitic G. australe, of which the mycelium causes a white rot with
selective delignification, that is most detrimental to Acer,
Platanus, Populus, Salix, Tilia, Aesculus (Anne Frank tree) and
Quercus rubra.
Gerrit
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