Thin spots in pepper plants' stems
So about a month and a half to 2 months ago I started some Ghost Peppers, Cayenne, Habaneros, Jalapenos, and Thai Chili Pepper plants from seed indoors. They started off great and after I saw 4 leaves, they all got transplanted to clay pots.
I started moving the plants outside onto my covered porch for a little bit of time each day, gradually increasing until they sat out there all day for about the last 2 weeks.
Two days ago, I set them all outside in the sun for a half hour, and then yesterday for an hour and now today the smaller 6 plants all have a thin spot in their stem right where the stem goes into the soil.
It seems to be only about a 1/4 inch section, but it goes from normal stem width to super skinny like a hair back to normal width and the plant looks like it is dying.
What happened? Did I put them into the sun too long? Too soon? Please help.