Question
WHAT WOULD CAUSE A SAGUARO TO TURN BLACK INSIDE AND LOSS ITS ROOTS SYSTEM? would it have a fungus?

Answer
Marlene,

Usually it is cause by either too much water or too much cold or both. We had a very cold snap this winter that damaged a lot of plants, including saguaro's. Unfortunately, that black stuff signifies the end of the plants life. It will eventually fall over, so if it is really big and close to your house, you may want to have it professionally removed. Sorry for the bad news.

Sincerely,

Greg