I found a leaf like this at the bottom of one of my tom plants today. It seems like an isolated case although some of the leaves at the bottom are generally yellowing/getting pale. There are no other issues with the plants and all are flowering and fruiting.

I've done some research online and it doesnt look like Early Blight or anything I could recognise from pics online.

I'd be grateful if someone can tell me what it is. The plant had a bit of a rough time in the hardening off process a while ago, but it's overcome that now.

Thanks!

http://www.flickr.com/photos/57048076@N06/7322890648/in/photostream