Please help me ID the killer of my plant :/

So, I grew two Hibiscus sabdariffa (Roselle or Sorrel, used for Hibiscus tea) from seed this year. Both of them took off fantastically, despite one being cut in half when it was just a seedling. They were planted with okra, each at the end of a long bed with plants two feet apart.

One of them suddenly started declining, first with severe chlorosis from bottom up, and then severe wilt, progressing from one side of the plant to the other. The plant was totally wilted and dead within a week. The okra and other roselle appeared completely fine.. the other roselle was even getting too big to handle.

When I started to cull the plant, a very foul smell was extremely obvious. There was no obvious decay on any of the main stems, the crown/foot, or any sign of anything unusual above the soil line, except for the odor. Wilted stems I cut to help with identification appeared totally healthy in cross section. Peripheral lateral roots that I pulled up first had no obvious decay

The crown pulled out of the ground with extreme ease, and then the problem became obvious. The inside of the crown and down into primary root was completely dark brown/black, decayed from the inside out. A light brown gel or slime was apparent on one side.

Weather conditions were extremely wet in June and into July, but it's been very hot and humid with no rain for several weeks. Soil is a nutrient rich, slightly alkaline clay with a nice layer of organic matter. Drainage is relatively good, because of the grade, the raised bed, and a french drain.

My first thought was cotton root rot, but I don't think the symptoms quite fit. I'm going to apply Actinovate to the adjacent plants as a precaution, as I have some left over. I'd appreciate any help!