Vegetable Production Problems 2007
Fusarium Wilt in Leon County
Fusarium wilt has occurred in Leon County tomatoes this summer. It was one of the first diseases known to affect tomato in Florida. As long ago as 1899, entire fields of tomatoes in our state were wiped out by Fusarium oxysporum f. sp. lycopersici. It can be an extremely difficult disease to control, in large part because it can survive indefinitely in the soil. The wilt cannot be overcome by simply thoroughly watering the tomatoes. More information is available in the linked publication.
A Series on Diseases in the Florida Vegetable Garden: TOMATO
http://edis.ifas.ufl.edu/PP121
Fusarium Wilt
Die off begins as the plant base 
Note green veins in yellow leaves.