I'd imagine..... don't think its a disease but rather a environment issue. Have you moved it indoors and outdoors often? I bet it is getting too much sun or too much water... yes that can happen.
However, after looking at your pics.... it looks like you have very rocky "soil" i've made this mistake before and the water literally goes right through it. I'd plant it in just some regular old dirt and get the roots grown up then mix in those rocks.
Sorry I wasn't much help... just giving it the old college try
