'Corroded' Tomato Stems

This year I am growing two varieties of tomato from seed - Super Mama and Costoluto Genovese.
I have grown both before without any problems and managed to get super plants with terrific yields.
This year, due to the CV situation, I struggled to get my usual general compost to plant on from my seed trays. I had to settle for a supermarket brand but it seemed to be ok.
However, one of the varieties (Costoluto) has really suffered from some sort of what looks like corrosion to the stems just at ground level. (see photos) I have lost about a dozen seedlings and even as the plants grew on some of the healthier looking ones just keeled over and basically had to be propped up to help them survive.
The Super Mama plants were also affected by some 'wobbling' but none showed such severe signs of the stem corrosion.
Both varieties seemed to have very bright green new growth when I planted them out.
I have now potted on the survivors with different compost quite deep to develop the stem roots.
Has any members experienced anything like this before ?
I've been growing tomatoes for ~40 years and never had a problem like this before !

Although the compost in the photos looks quite wet, that was due to pre-transplant watering. I had also removed some of the compost from around the stem for the photos.

 

Hi and Welcome to the Forum,

It does look like they have drowned, the compost as you say looks very wet and there are signs of algae growing on top, plus the compost itsself might be rather poor ?

Still time to sow some more seeds or you might be able to take cuttings from the good top growth, they are easy to root as we tried last year.
Hopefully you can get some good compost tomorrow when the garden centers open, but expect there will be a mad rush !

There is a Tomato 2020 thread for all such Q&A, well worth a browse.
TOMATO GROWING THREAD 2020

 

Looks a bit like damping off, fungal problem mostly due to not enough ventilation and soggy compost.

Are you letting the surface dry out before watering.

Think I would be mixing some sharp sand in with that compost.