Root rot?

[shafak]

In February, one fine day the bark around the base of this mulberry tree's trunk peeled off and something whitish appeared on it.  I did not pay much attention to it then as I was busy with other works. 



Then, in mid March, all of a sudden this tree died.  Was it due to root rot?  I don't want to have a repeat with the other remaining plants.  Thank you.