Answer: That is a tough one! Possible causes of sudden wilting and death include Verticillium wilt, Fusarium wilt, Southern blight and nematodes. All are soil borne. The first three are why gardeners look for VFN tomato varieties, which are naturally resistant to these two fungal diseases and nematodes. The fact that you planted 10 varieties, and most if not all were affected tends to eliminate the V, F, and N possibilities.
Southern blight resistance is not currently available. Once the soil has these pathogens, it will continue to be infested for a number of years.
The puzzling fact is that all of your plants apparently were infested at about the same time. These diseases (and nematodes) tend to affect plants here and there, but not usually all at once. It is possible however that the plants came in with infested soil or that the entire planting area was infested before planting.
The black blemishes on the bottom are a sign of blossom end rot, usually related to a lack of calcium. This doesn't cause plants to rapidly wilt and die, but may be another symptom of the other diseases or nematodes damaging the plants water and nutrient system.
The only practical way to prevent this problem in the future is to move the planting to another area. Also, make sure and select VFN resistant varieties.
Thanks for the question!
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