[derek_mcc (OP)]

I have attached a picture of an apple that has fallen in our garden and was left to go mouldy.  The mould is in small (1 to 2 mm) round-ish colonies, but these have arranged themselves into lines.  This gives it a zebra-striped appearance.  Why would this be?

[CliffordK]

That is bizarre.  However, is this apple a home-grown apple, or a store bought apple?

[derek_mcc (OP)]

Home grown - it fell from the tree and got missed when we collected.

[RD]

http://en.wikipedia.org/wiki/Reaction-diffusion_system ? ...



like fairy rings ...


http://en.wikipedia.org/wiki/Fairy_ring

or the Belousov-Zhabotinsky reaction ...

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http://www.youtube.com/watch?v=bH6bRt4XJcw

[CliffordK]

I was hoping one could blame it on some kind of a commercial processing such as waxing. 

Is it just one apple that has that mold pattern?  I'm wondering if it could be a chimera, or mosaic, in which the different cell lines might have different resistance to rot, or perhaps different skin texture.

[derek_mcc (OP)]

This is the only one that I have noticed like this - but I'll scout around in the light tomorrow and see what I can find. RD's post has some mileage; the colonies might secrete some inhibitor that diffuses away from them, or they are limited by the amount of nutrient they can derive from the apple so can't colonise it all???

[Bored chemist]

Mold like that is pretty common on apples etc. I grew up in a house where there were a lot of trees in the garden so I have seen plenty of spoiled apples. I presume it's the equivalent of a fairy ring (why would it be different?).

[Lmnre]

Curious: Has the mold formed several rings (plural) or one continuous spiral (singular)?

[RD]

mould can exhibit the Belousov-Zhabotinsky pattern ...

 [ Invalid Attachment ]
www.youtube.com/watch?v=wvRxoiiGCWY



http://en.wikipedia.org/wiki/Belousov%E2%80%93Zhabotinsky_reaction#History

[derek_mcc (OP)]

The original apple has gone to the great recycling centre in the sky, but I found a couple with similar markings.  Looks like the older colonies have gone black.  It seems more like concentric circles than a spiral - but it isn't such a clear cut pattern that it is easy to be definitive.  I am sure it could be the Belousov-Zhabotinsky reaction - but what is the mechanism?  Something - an inhibitor perhaps - diffusing from the colonies?  There were lots of other apples going off with a blue/grey mould which didn't show any pattern, unlike this white mould.  There were also plenty rotting away with no (visible) mould at all.  Perhaps each apple (or part of an apple) is its own micro-environment.

[derek_mcc (OP)]

And another picture ...

[RD]

  I am sure it could be the Belousov-Zhabotinsky reaction - but what is the mechanism?
 Something - an inhibitor perhaps - diffusing from the colonies? ...
...  Perhaps each apple (or part of an apple) is its own micro-environment.

Maybe a combination of invisible bacteria + visible mould produces the pattern ...
the bacteria breakdown the apple which makes it more digestible by the mould,
but the mould excretes antibiotic to stop itself being eaten by bacteria, [e.g.]

The action of the bacteria on the apple promotes mould growth ,
but the mould locally inhibits the bacteria by releasing antibiotic ...

In the center of the plate is a colony of Penicillium notatum, a mold that produces penicillin. After appearance of the mold colony, the plate was overlaid with a bacterial culture of Micrococcus luteus which forms a yellow "lawn" of growth. A zone of inhibition of bacterial growth surrounds the fungal colony where penicillin has diffused into the medium.

http://textbookofbacteriology.net/themicrobialworld/bactresanti.html

[CliffordK]

Unfortunately (or Fortunately) I have deer...  and thus very few moldy apples.  As a side, I will also mention that the deer are also good at controlling apple maggots which have a life cycle including chewing into the apple, then the apple falling onto the ground, and the maggot going into the ground, and hibernating until the next growing season.  Keeping the apples clean from under the trees helps break the cycle.

Anyway, back to the original question, it is interesting that the circles seem independent of the stem/bottom of the apple, which would tend to indicate it is less likely a feature of the apple, and more likely a feature of the mold growth.

When the apple falls on the ground, you tend to get a bruise in one section of the apple, which I believe locally accelerates decay.  It is quite possible that starting at the bruise, the decay would progress step-wise across the apple.  One would expect to see a growing blob of mold from this original bruise, but perhaps as RD is mentioning, it may be some kind of an Angel Ring effect, and possibly an interaction between bacteria and mold.

Mold forms hyphae, and thus the subsurface mold may be extensions of what you're seeing on top, somewhat like the angel ring mushrooms have an extensive subsoil root network.

There are also some dimorphic fungi which can take on mold form, or yeast form.  Perhaps you have yeast fermentation + mold growth, somehow creating the rings.

[RD]

Someone agrees with me (I think) ...

[ You are not allowed to view attachments ]

http://books.google.co.uk/books?id=gTb5AkmX3-gC&pg=PA94



"map a Reaction-Diffusion pattern to a sphere"
http://www.bugman123.com/Math/

[chris]

My first thought on seeing that patterning / distribution was diffusible signals moving away from the colonies producing bands of inhibition. Why they form concentric rings around the apple circumference though, rather than isolated colonies surrounded by circular inhibition zones, I'm not at all sure. I'll find a friendly fungus person I know - given that it is "Fungus Day" this weekend - and ask her...

[Ali_A]

Oh how pretty! Its Sclerotinia fructigena by the looks of it – I have some growing on pears in my greenhouse for an exhibit especially for UK Fungus Day at the Cambridge Science Centre this weekend! The fungus causes brown rot of apples, pears and some other fruits with infection caused commonly through wounds but sometimes insects and earwigs – these buff coloured pustules are conidia (asexual spores) of the fungus and they often appear in concentric zones. Sporulation is stimulated by light and adjacent zones correspond to daily periods of illumination – the fungus mycelium grows out in a concentric pattern and light stimulates sporulation - hence the concentric pattern of pustules on the fruit.  Hope this helps Chris!

[chris]

Wow - that's amazing - so it's driven by light; I guess this is crying out for someone to do the experiment and rotate the fruit to see if sporulation can be driven at ninety degrees to the initial lines... volunteers?

(And thanks Ali!)

Chris

[Bored chemist]

I'm not sure that sporulation has a direction any more than sleep has.
The mycelial growth might be directional.

[RD]

... rotate the fruit to see if sporulation can be driven at ninety degrees to the initial lines...

If the rings of mould were rippling out from one point of infection, with a daily cycle , [ e.g. comparable with tree rings, but daily rather than annual ] , then an apple infected at two points could be covered with squares, e.g. like this simulation  ...

 [ Invalid Attachment ]  [ Invalid Attachment ]
( I've never see one like that )


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I'm not convinced this zebra pattern is formed by [8? equal?] daily doses of sunlight,

The reaction-diffusion mechanism can produce B-Z patterns in slime mould without sunlight ,
so daily sun isn't necessary for mould to have this type of pattern.

Some moulds pulsate of their own accord [without a zeitgaber] ...

An interference pattern is possible where there are [pulsating] waves,
but I'm sticking with a reaction-diffusion mechanism to explain the zebra-apple ...

Today, Alan Turing is best known as the father of modern computer science, but in 1952 he sketched out a biological model in which two chemicals — an activator and an inhibitor — could interact to form the basis for everything from the color patterns of a butterfly’s wings to the black and white stripes of a zebra.

http://news.harvard.edu/gazette/story/2012/04/turing-was-right/

The Chemical Basis of Morphogenesis     A. M. Turing

...  A system of reactions and diffusion on a sphere is also considered. Such a system appears to account for gastrulation ...

http://rstb.royalsocietypublishing.org/content/237/641/37


[ also see "pseudo-zebra" on page 5 of this paper ... "Generating Textures on Arbitrary Surfaces Using Reaction-Diffusion"]

[derek_mcc (OP)]

Thanks Ali.  You are saying that the fungus grows outwards from a the point it first got in - so it will spread out in a circular fashion over the surface, growing day and night.  However, it only produces these spores in daylight, hence the concentric circles.  If this is a "pretty" example I could let you have the full sized image for your collection if you like.