Dear Ranganathan

That depend on plants drought or osmotic stress tolerance, environmental parameters and etc. But you can calculate osmotic pressure of 50 gl-1 peg 6000 by references below,  in our researches indicated that 150gl-1 (about -5 bar) induce enough stress for biochemical responses in wheat and more than 150gl-1 have same effects on Cali in  tissue culture environments.

Dear Ranganathan

First of all you need to check the osmotic potential of your PEG solution through osmometer for accurate research. However, 50g/L creates nearly -0.5 MPa osmotic potential, which induces mild drought stress in plants. I recommend you to use higher osmotic potential solutions (-10 or 1.2 MPa) of PEG 6000 for inducing drought stress. you can also follow our paper in this regard