Lima Acidless Orange tree showing a problem

I've had this medium Dwarf acidless orange tree since 2001. It doesn't seem to really grow much but at least last year into this one it bore some fruit.
It has a problem with the bark and I'm not really sure how to deal with it, it seems to be "barkless" in certain areas, where the bark has disappeared...
Maybe posting some pix on here will help id the problem... you can't tell much from this one but it just shows the size of this little tree.
If you have an idea please let me know what to do... thanks in advance!

Apparently the latin name is Vainiglia sanguigno but I haven't found a lot of info on it yet, I'm just starting to look into this problem.
This spot shows the barkless area. It also is displaying some blackness on the bark as well which doesn't look right.

'nother view of the bark.
These trees make a great conversation piece. Tell people that it doesn't have citric acid you get looks of disbelief.
Only when you let them sample the taste do they get it.

the whole trunk seems to have turned black. Maybe a fungus?

I think the bark was sun scorched. Citrus bark is very sensitive to damage. That is why citrus trees are allowed to grow naturally almost all the way to the ground or a white wash made from latex paint and water is used to protect the exposed bark. The black is probably a fungal disease called sooty canker which grows on damaged tissue. Sun scorched branches usually die. It depends on whether the damage extends all the way around the branch.

Sun scorched? Hmmm. Where it has been kept it hasn't had that much sun. Not like it's been kept in the shade, but I doubt if that's the case...
Is there a treatment I can get for the fungal disease maybe at Lowe's or Home Depot?

Since citrus is such a huge industry in California, you can find tons of hep from UC's Cooperative Extension Service. Here are some links regarding sooty canker and links to UC's Extension Service.
http://www.ipm.ucdavis.edu/PMG/C107/m107bpfruitdis.html
http://homeorchard.ucdavis.edu/links.html
http://news.ucanr.org/UCLinks/uclinks.shtml
http://cesandiego.ucdavis.edu/
http://www.ag.arizona.edu/pubs/crops/az1032.pdf
http://www.answerbag.com/articles/How-to-Treat-Sooty-Canker-Fungus-in-Trees/1e14d7b0-db5c-5c53-509e-18fb8a00beee
It is possible that the tree has sooty mold. In that case look for aphids or scale. Sooty mold feeds off the honeydew from sucking pests, such as aphids or scale. It's unsightly, but not really a problem unless it covers the leaves so thickly that it interferes with light absorbtion. If it is sooty mold, you need to get rid of the aphids or scale. The mold can be gently scrubbed off using water and a soft sponge.

Fondofronds, Can't tell from your photos, but you might want to search the the web for info on a citrus disease called gummosus. Another good source for citrus info is UCR.

Do they take direct inquiries at UCR? Usually, you have to go through your local Extension agent and they will forward all questions.

thanks for the info everyone...
I will be looking into it!

No one said this but do you have any animals that might be rubbing up against that??? Over time that might produce a hole???

Just a thought.

That tree is not getting any rubs from anything.
A good thought but that is not the problem.
thanks...

I've had a few dog incidents.

Gummosis is not spelled gummosus as I previously did. My bad.