[avs0020]

Hi everyone. Does anyone have ny idea what is happening to the base of the stem of this little impatiens Balfourii seedling. Out of a tray of 12 half are affected (and its an intermittent arrangement - not like all the seedlings on the left).

I have checked the soil and there is no visible "pest". The photo looks like the stem is being stripped but its almost like its dried out from the inside outwards and has a tougher feel to it than the rest of the stem. The stem at the base is much more thinner than the stem up towards the leaves which are now beginning to wilt. So disappointed because I have nurtured these chaps since late Feb. Thanks for any advice.