I recently planted some sunflower seedlings and they have been doing fairly well. The only problem I had noticed was that the tips of the leaves were slightly burnt, but even then, the burns weren't spreading and the plants seemed to be doing fine. In the past couple of days, however; the stem of one of the seedlings became shriveled mid way up the stem. The strange part is that the base of the stem is fine, and the top of the stem too is fine.
I have no idea what is wrong with it. My only guess is that the soil is too basic.