Why precisely are you interested in the use PGR to stimulate the growth and not other ways? Remember that hormones are used in very low concentrations by plants to regulate their own ontogenic development. An unbalance of them might cause important disorders and undesirable effects, quite different to those that you are looking for. I could advice you some other (more) "friendly" ways e. g. a suitable and nutritive substrate, chemical fertilization, mycorrhizae, humus (foliar spraying or incorporated to substrate), among others. I don't know if you have tried these or other methods before or if they will be useful for potato but you could obtain good benefits from them. Good luck.
i using nutritive substrate like amino acid or protein contain which were prepared from sea weeds..or related source ..getting good results .
sir now in the mark ate lots of products with Plant growth regulators/ retardants are there which used on potato to increase its yield by both ways as weight as well as number tuber/ plant so interested to try that ..one
sir as u mansion on conc. of PGR use i well stack on that