Plant Growth Regulators (PGR): Organic compounds which are occuring naturally in plants as well as synthetic other than nutrients which in small amount promote, inhibit or modify any physiological process are called plant growth regulator. The plant growth regulators are of two types:

i) Growth promoter e.g. auxins, gibberellins & cytokinin.

ii) Growth inhibitors e.g. abscisic acid and ethylele.