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Pleurotus ostreatus -   Oyster Mushroom 

A hundred million spores and hour!

Table tops in labs are often black.  I think this is probably because black doesn't show the stains of sloppy technique as readily as other choices.  Also, the wear and tear caused by pieces of equipment dragged across the surface will be less evident.   Whatever the reason it certainly had an advantage in the photograph above of the Oyster Mushroom. 

The cluster of mushroom caps came in at the end of the day and was placed rather casually on the lab bench surface where it would hopefully receive some attention the following morning.   When I came in the next day, I was pleasantly surprised to see the scene above.  Like snow in summer! 

The Pleurotus  had discharged its spores through the night and even though it was lying right on the lab bench surface it showed a remarkable ability to disperse the spores.  You can see the thickness of the deposit where I have removed some objects that were lying on the bench in the vicinity of the mushrooms.  Also, remember that the spores of Pleurotus measure only about 8 X 4 microns and individually are invisble to the eye.  So on the black parts of the bench there are also millions of these 'invisible' spores but they are spread around so thinly that they do not show up as white.   Goodness knows how many spores were floating around in the air of the lab that day.  How about allergies?  Check a little further down the page.

The numbers of spores produced by mushrooms is impressive.   Estimates have established that a good sized mushroom will release its spores at the rate of 100 million spores an hour.  Spore release is not constant but will fluctuate during the day depending on temperature, humidity age of fruitbody etc. but a figure of a billion spores a day would not be out of order.  

And this is nothing compared to the giant puffball (Calvatia gigantea).  I once gave my mycology class the project to calculate the number of spores in a puffball I had on display in the class (about the size and shape of a turkey, click here for photo of Calvatia and Heather Sutton)    We took a small clump of puffball 'stuff' and weighed it.  We then put this sample into 100 ml of saline solution with a wetting agent and shook it up vigorously for a while.  A drop of this spore suspension was placed on a haemocytometer and we measured the concentration of spores per ml of suspension.  we then calculated how many spores in the sample.  Knowing the weight of the sample and the weight of the whole puffball, we calculated the number of spores.  The answer was  about 1,000,000,000,000!  Staggers the mind!   On the other hand, maybe I should have checked their arithmetic!


I then asked the students a very important biological question. 

What happens to all the spores from  a mushroom, a puffball or whatever?

The answer of course, if you think about it, is that they probaly all die and at best only one will survive. 

To understand the fungi you have to appreciate that even with odds of billions to one against a fungus will survive and be successful.

Mushrooms, puffballs, boletes, polypores and all the rest of the fruitbodies of the so-called macrofungi are amongst natures most sophisticated biological designs for spore production.  The current spectrum of spore producing fruitbodies of macro fungi that we see in field guides are the successful survivors of   countless millenia of  experiment, refinement and selection.   If the survival odds are as low as we have indicated you can appreciate the selection pressure to get it right!

Many mushrooms, however,  produce only a few fruitbodies, or have only a few well-spaced gills, or shallow gills, or small caps etc.   There limited spore producing surface (hymenium) produces only a tiny fraction of the number of spores that the big guys do.   Yet they are still successful.    If spore production is a primary criterion for success how do you explain this?   Easy question, obvious answer!

How about allergies?

You can imagine that, in the fall season with all these fungi distributing airborne spores,   you could have a real problem with allergies.   Spore counts of fungi in air fluctuate dramatically from season to season and even from week to week.  But it is not unusual for the clean country air in the fall to contain 10,000  spores or more per cubic metre and it would not surprise me if some people showed severe allergic responses to this level of exposure.   Mould allergy tests would not reveal this, however, as few if any of these airborne mushroom species are represented in allergy testing procedures. 

You can now buy the Oyster Mushroom in supermarkets.   It grows quite nicely in commercial mushroom houses.  As the mushrooms reach maturity, the level of  spores in the atmosphere of the mushroom house must be incredible.  I wonder if they monitor airborne spores (bioaerosols) in mushroom houses for Oyster Mushrooms and if it is a serious health hazard to the pickers.   Perhaps  Pleurotus is harvested by machines.   I'll have to check on this. 

Note: The common commercial mushroom (Agaricus)  is picked at the button stage,  before it is mature enough to produce any spores (in theory!).