Could be this stem rot that affects jute where it is grown:
The causal organism- Macrophomina phaseolina(Tassi) Goid is a dreaded pathogen and it can infect more than 500 plant species in about 72 families.
https://krishi.icar.gov.in/jspui/bit...%20_review.pdf
If so it's an ascomycete fungus. IDK if it would survive outdoors here, since it is tropical in origin. Will search further before I decide about composting.
Hmmm Sclerotinia rot is also mentioned in the same - that affects jute and is known to affect tomatoes. And i think the pics are a best match for what I've got.
Anyone have experience controlling 'timber rot' 'white rot' 'sclerotinia rot' on tomatoes/ and/or in the soil?