I have successfully germinated 10 lettuce seeds from a tissue and transplanted them into a pot. They grew more and showed new leaves, but after some time I noticed that their stem from the base started to turn brown and become thinner.
I googled it and I confirmed that my lettuce seedlings experienced what they called damping off. I read about how to prevent it and many said that the soil must be baked in an oven or sprayed with some anti-fungal, but that's not advisable because it may be toxic to plants and to people. The problem is that we don't have an oven to use and even if we have, my mother will not allow that method.
The next possible thing I can do is to let the soil dry from the sun but I don't if it's OK to do that, or are there other alternatives to prevent damping off from occurring again?