What is this disease?
 

I ran across this picture today while I was going through the yearly photos of my gardens. Several years ago (2010 to be exact) I grew Red Brandywine, and nearly overnight its leaves started turning a bright yellow (all over the plant). The chlorophyll was gone! That was the only time I've ever seen anything like this this in hundreds of different varieties that I've grown.

Any thoughts as to what it might have been?

-GG