Save The Beans!

So, I may have mentioned that I recently received some seedlings that I hope to grow to the edible stage in the sunroom this winter. Among them were fairly hearty bush bean plants. They are all potted up- but one of them seems to be dying and I have no idea why. The leaves seemed to curl and then the stem withered, but not at the base- more out the branches. So, I was disappointed, but not too worried since there are five more. But now I am wondering if the plant next to the dying one is also on the decline. Most of the plant looks great, but one section is starting to look iffy. I will probably cut that part off tonight in hopes of stopping whatever this is. But I see no obvious evidence of... anything! Help! Does anybody have any idea what this might be? Save the beans!