Just wanted to add (forgot to mention this in the other post). If you do in fact think this is rot you should remove it from the soil as soon as possible. Use something clean to cut the rot away and keep cutting in small sections until there is no more visible rot. Then dust with cinnamon and let dry for a few days before setting it back in soil and waiting for roots. May also want to use rooting hormone at that point.

The experts should be along shortly to clear anything else up and give advice :)