Sorry you didn't get a response. I didn't know and I hoped someone else would. When I saw your post was still sitting here I went looking. I think I found the answer, but unfortunately it is all bad news. I believe this is Southern stem blight, aka southern blight, white mold.
It is a plant disease that usually only occurs in warm areas (hence the southern). You didn't say where you are.
Here's one picture of it I found, looking pretty much like yours.
https://beanipm.pbgworks.org/sites/beani ... k=g983O5e1
It usually occurs like yours on the stem down near the soil, but can spread to any parts that are near the soil, such as if leaves or fruits are hanging down. And it spreads down into the roots.
It is pretty deadly and there is no real cure. They say as soon as you spot it on plants, you should remove and trash the whole plant (not in compost pile), to try to prevent it from spreading through your garden. Many plant diseases are specific to one type of plant or one family of plants, but unfortunately this one can infect over 500 different plants. So if you don't get it out of your garden, it can take over your whole garden. The spores and maybe other parts of the disease organism are in the soil, so you can try treating your soil. That would be with heat treatments, including solarization (look it up), soil drenches of fungicides, deep plowing, and then adding a lot of bioactive compost.
Most important is prevention, especially now that you know it is in your garden. It likes warm, moist conditions. So you want to keep your garden as dry as you can and with good air circulation. Keep your plants well spaced and pruned so as to promote air circulation. Water as little as you can (infrequent deep watering) and only water the soil. Mulch heavily to prevent soil from splashing up on to the plants.
All fungicides whether organic or chemical/synthetic work better as prevention than cure, especially for this disease. So start from the beginning of the season spraying all your plants with fungicidal sprays as well as drenching the soil. Respray the plants every couple weeks or so. Organic fungicides include hydrogen peroxide, diluted milk, baking soda, compost tea, Neem oil. You can rotate them to see what works best.
Sorry to have such bad news for you and sorry for the delay getting it to you. Keep us posted what you try and how it is going.