What tomato disease is this?

I recently lost two young tomato plants and the symptoms were similar:
1. First the plant started wilting a bit in mid day and the crown looked dark and wet
2.  black streaks appeared along the stem and the base of leaves went mushy
3. The lesions travelled upward and the inside of the stem rotted away and whole plant was not salvageable
4. It developed very fast within two days.

I am suspecting it was caused by soil borne pathogen on that specific location: I planted two different kinds of tomatoes in that bed and they were both down, while tomatoes somewhere else are fine including the same variety.

I took some pictures. Let me know if you know the name of disease, thanks.

Could be Alternaria alternata fungus or Alternaria stem canker.

I looked up the pictures and those stem rots seem to be more dry and limited, not killing the whole plant immediately. Maybe because these two plants were young (7 weeks) and the tissues were softer.

I put a stake by the tomato on Monday morning, 6 inches away from the stem. Maybe some roots were injured and the pathogens infected the wounds. Anyway, hours later in the afternoon the plant started to wilt. I cut off the top 6" hoping it wasn't infected up there yet. And it wasn't, two days later, the cutting perked back up and there was no stem rot. The rest of plant turned mushy gradually on Tuesday. When I pulled it this morning, the root ball looked normal.

I was quite astonished by how quickly the symptoms developed, if the infection was indeed initiated by the root injury. I had no idea what happened to the first plant died last week, maybe because of a chicken scratching the ground?

I think it may be a bacterial blackleg infection. There is a fair amount of information about the disease in potatoes, but I think it can affect tomatoes too. This article gives an overview of the disease and this one describes in more detail the way it affects potatoes. It is soil borne and also survives in infected plant material.

It does look like potato blackleg, thanks.
The spot used to be the strawberry patch and the soil hasn't been amended much. I am not growing any more tomatoes there. The disease is so devastating.