I am an amateur naturalist trying to discover everything living in my garden.
I have a cooking-apple tree growing in my garden (more on which in a future posting). It produces far more apples than I can cook and winter finds my lawn carpeted with a layer of rotting windfalls. At the time of writing, a flock of songbirds (blackbirds, thrushes, redwings, starlings, fieldfares and others) are visiting my garden daily to eat their fill. Birds are not the only things devouring my apples however...
Photo 1 (click to enlarge) shows an apple clearly afflicted with an outbreak of brown scabs. Recently I acquired a second hand copy of Garden Pests and Diseases (Brooks and Halstead, publ. Simon and Schuster) and from this, and some follow-up searches on the internet, I understand the cause to be a fungus called Venturia inaequalis.
V.inaequalis infects both the leaves and fruit of apple trees and is a member of the enormously numerous division of fungi, the ascomycota = those fungi that "ripen" their spores inside tiny, sausage-shaped tubes called asci (see here for my photo of some asci and here for some more description from me).
In the case of V. inaequalis the spore-containing acsi are, in-turn, packed inside a body known as a psuedoperithecium (a "spore salt-shaker"). I made a little effort myself to try to obtain a microscope photo of one of these, but the strength of my resolve was weakened when I found the matchless images on Tom Volk's website (in any case, I believe I'm unlikely to find a 'fruiting' scab as I've read the pseudoperithecia tend to occur in Spring and are more common on the leaves).
In terms of edibility, brown scabs on apples are entirely harmless (no doubt the same can't be said of the fungicides commerical growers spray on apples to prevent scabs appearing!). Indeed, I've even heard it suggested that amongst the reasons for an increased incidence of cancers in the Western population is our unwillingness to imbibe a healthy population of micro-fungi on our vegetables. I can't vouch for the scientific validity of this theory. I do know you'd need to be very hungry to eat the apple in photo 2!
Looking closely at photo 2 you might notice the small white patches of mould upper left and centre. Viewed under the microscope (approx 40x magnification) a strange and delicately beautiful structure is revealed (photo 3).
On the basis of looks alone (always dangerous when dealing with fungi) and the excellent photo's on this site, I'm identifying this as a member of order the mucoraceae, the 'pin-head' moulds. The 'pin-heads' are technically known as sporangia and are filled with spores. They turn black as the spores mature (as some have in the photo).
To attempt to pin down my mould to one of the three-hundred-or-so mucoraceae species is really the domain of experts. Increasingly DNA analysis is emerging as the only sure-fire method for the identification for micro- (and indeed some macro-) fungi. Taking a shot-in-the-dark however I'll go with Rhizopus stolonifer and invite the experts out there to correct me.
V.ineaqualis and and R.stolonifer are far from the only fungi to attack apples (see here), I'm quite sure more searching would turn up more (a project for a future posting perhaps). For now I'm happy to chalk-up two more species on my garden checklist.
Finally, I mentioned the birds above feeding on the apples on my lawn. Watching them it seems they actively seek out the more rotten apples. I wonder whether they get some health benefit from this (the consumption of pencillin moulds perhaps?), or is it simply that the mouldy ones are the softest and best-tasting. A case of Stilton cheese at Christmas!