Apple tree needing some help!

[Chunclepaul]

Hi all, I have an apple tree in my garden and we have noticed a few issues around the base, the tree (I have been told) is approx 50yrs old. I have added pictures for context.
The issue you will see is the hole, this is filling with water, there are slugs and worms living in it... what's happening to the tree? My wife loves it and I wanted to try and save it as it doesn't look good... any advice would be greatly received.

Thanks in advance..

[ameno]

The heartwood is rotting out. This is quite normal in old trees.
In trees, only the outermost inch or so of wood is actually alive. Everything in the centre is dead, and it's only purpose is to physically support the tree. So if the heartwood is exposed somehow (by the looks of it, a branch was cut off there many years ago) then wood rot fungi will eventually start rotting it.

The heartwood is already dead, and the wood rot fungi cannot grow in living wood, only dead wood, so although it might look bad they will do no direct harm to the tree.
It can do indirect harm to the tree by weakening the trunk and thus making it more prone to falling over in strong winds, but there isn't really a lot you can do about that, short of maybe trying to build some sort of frame to shore the tree up.

So it's fine to just ignore it, and try not to worry too much about it. The tree may topple over eventually (especially if it is growing lopsidedly), but that will likely be quite some years hence yet, if it happens at all.
The only reason to be at all concerned about it is if there is something like a greenhouse or shed which might be damage if it falls on it.

[Chunclepaul]

Thank's so much for taking the time, I do feel reassured and slightly sad, but that's nature...

Is there anyway to fill the gap to reduce the rotting at all or would it be a lost cause??

Thanks Again :-)

[Nicos]

I’m watching this thread as my plum tree has a massive open wound where a branch ripped off in the wind a few weeks ago

Interesting advice ameno- thanks