Role of growth regulators in agriculture :
1. Parthenocarpy : The knowledge of the fact that application of auxins and gibberellins on unpollinated flowers results in the production of seedless fruits has been a great horticultural importance. It has been of great significance in such fruits where the number of seeds is very high and the seeds are of light food value (e.g., tomato, brinjal, guava, papaya, watermelon, orange) or the seeds are large in size (e.g., Litchi and Mango).
2. Flower thinning : This problem refers to fall of unpollinated or unfertilized flowers from certain fruit trees e.g., in pineapple and litchi. This problem has been solved to a great extent by spraying the plants with 2, 4-D and Naphthalene Acetic Acid (NAA) both of which are synthetic auxins.
3. Fruit ripening : Ethylene plays an important role in ripening of various fruits like oranges, lemons, grapes, banana etc.
4. Rooting inducing or Root induction : NAA and Indole Butyric Acid (IBA) are very important in inducing roots on stem cuttings. Many plants are known which propagate by their stem cuttings such as Bougainvillea, roses, grapes, apples, coleus etc.
5. Seed germination : Seeds having long periods of dormancy can be made to germinate early by the application of auxins.
6. Potato storage : Some auxins e.g., methyl ester of naphthalene acetic acid is used to store potatoes for long periods.
7. Weed control : 2, 4-D is and Tricholorophenoxy acetic acid are specific killer^ of dicot herbs and are called herbicides. Thus in a field having monocot crop dicot weeds may be eradicated by spraying either 2,4-D.
8. Genetic dwarfism: When a genetically dwarf plant is treated with gibberellins it grows tall. Examples are pea, corn and bean.
9. Effect on bolting and flowering : Another specific example of the action of gibberellins is inducing stem elongation and reproductive growth. In many plants leaves are developed in the form of a rosette and internodes remains short in first year of growth. Just before flowering internodes are strikingly increased. The phenomenon is known as bolting.