UKTC Archive

RE: Ganoderma applanatum/australe on n.maple - implications

Subject: RE: Ganoderma applanatum/australe on n.maple - implications
From: David Lonsdale
Date: Dec 23 2011 13:31:53
Dear Gerrit,

I agree that we can get some interesting clues from the observation that some 
decay fungi seem to "die with the tree", whereas others survive afterwards 
for many years.  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 (as defined, for example, by Ainsworth & 
Bisby), cannot be applied to any decay fungus.   On the other hand, I agree 
entirely that there are important distinctions between different decay fungi, 
with regard to the capacity either to grow  or not to grow in living sapwood 
(or in living versus dead trees).

I think that that these distinctions can be summarised as follows:

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. 

I can think of the following reasons why a fungus "dies with the tree":

1. The fungus has used up all the wood that was available to it, and so it 
runs out of energy.  There might still be plenty of wood left, but certain 
fungi are not easily able to continue using wood beyond a certain stage of 
decay.  Others, such as Polyporus squamosus, are easily able to continue 
decaying the wood until almost nothing remains, and so they can survive for a 
long time in a dead stem or stump. The same is probably true of Ganoderma 
applanatum.

2. After the death of the tree, there are physical and chemical alterations 
in the wood.  I am thinking, for example, of the disappearance of sugar and 
starch, which are soon used up by microbial activity after the tree dies.  
Perhaps some decay fungi depend partly on these simple carbohydrates in order 
to continue causing decay, and so they tend to die with the tree.  Also 
moisture-content (and therefore the aeration) of the wood changes after the 
death of the tree - perhaps enough to kill the fungus either by an excess or 
a deficiency of oxygen.  I have circumstantial evidence that Meripilus 
giganteus, for example, is sensitive to oxidation, although it often survives 
for years in dead roots. 

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).

With regard to the fungi that you have described, there is probably a need 
for research in order to find out what is happening on a microscopic scale.  
I can only try to make some guesses, informed by what I believe to be general 
principles, as follows:

1. 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.)  I would 
guess that its "death with the tree" is caused by altered conditions in the 
wood and/or by competition with other organisms.

2. Inonotus cuticularis and Meripilus giganteus:  I have very little personal 
experience with I. cuticularis, but there is circumstantial evidence that M. 
giganteus can die out in a living tree after it has used up a volume of wood 
that was available to it.  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.

3.  Phellinus tremulae: I have seen this fungus in Sweden but have no other 
experience with it.  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, now that we know that latent colonisers of living sapwood 
(often called endophytes) usually develop after the sapwood is damaged and 
exposed to the air.)

4. 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 (in my category "C", above).   On the 
other hand, I do not know of any detailed studies to prove this.  Also, I 
have not seen any evidence that this fungus kills trees as a whole.  Perhaps 
this fungus is using wood that is already dead and that occupies a large 
volume because of injury or aging.  If so, it would be a saprotroph that has 
the ability to grow in the already-dead wood of living trees (in my category 
"B", above).

Kind regards,
David


-----Original Message-----
From: Viper Snake [mailto:snake24@xxxxx.nl]
Sent: 23 December 2011 10:39
To: UK Tree Care
Subject: RE: Ganoderma applanatum/australe on n.maple - implications



 
Dear David,
 
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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