fdd2blk, Nematodes is one of the people who commented in this post. as for "Beneficial Nematodes", they would only help if fungus gnats or other pests are present in the soil.
the pot's do look large (I agree) but you can't tell how tall they are, it looks like they barely have any soil, so not knowing what the soil makeup is (MG, FoxFarm, etc...), PH, watering cycle (and if the dirt is dry or wet before watering), what type of water being used, etc... everyone's answers could be right.
It's like walking into the doctor and saying "I'm sick" and not disclosing anything else or allowing an examination, so your doctor would only speculate and would need more information before he/she can properly diagnose the illness. As stated before anyone would need more information.
I had plant's that size and they out grew a 1.5 pint pot after 1.5 weeks of veg.
over watering? possibility if there is not enough or to much soil/soilless mix in the pots, is there perlite, the soil/soiless mix doesn't drain well, and/or watering when it is still wet.
Nute Burn? possibility due to the makeup of the soil/soilless mix. feeding to early can cause this too.
Nute Lock? possibility.
Cal/Mag deficiency? possibility due to the makeup of the soil/soilless mix, water used for watering (tap water can cause this), etc...
PH problem? could be, what is the PH of your water? are you using tap? bottled/filtered? RO?
Other problems? yes, but speculation is all you'll get with what little info is supplied. you'd get the same random solutions from any well known garden center (let's say you grew tomatoes). In order to help you out they would ask a list of questions to aid in diagnosing your problem and guide you in the right direction.