Primary Classes of Plant Growth Regulators
Plant growth regulators are broadly categorized into growth promoters that stimulate cell division and expansion, and growth retardants that inhibit vegetative elongation.
Understanding the specific hormone class ensures targeted agronomic intervention.
- Auxins (Alpha NAA, IBA): Prevent flower and immature fruit drop, stimulate adventitious root cutting formation, and regulate apical dominance.
- Gibberellins (Gibberellic Acid / GA3): Stimulate stem elongation, enlarge seedless grape berries, and break seed dormancy.
- Cytokinins: Promote cell division, delay leaf senescence, and stimulate lateral bud development.
- Ethylene generators (Ethephon): Accelerate uniform fruit ripening in bananas, mangoes, and tomatoes, and induce synchronized flowering in pineapples.
- Growth retardants (Paclobutrazol, Chlormequat): Inhibit gibberellin synthesis, controlling excessive canopy rank growth and inducing flowering.
Precision Dilution and Safe Application Rules
Because PGRs operate at microscopic physiological thresholds, precise measurement in parts per million (ppm) or milliliters per liter is essential.
Applying excessive dosages can cause leaf epinasty, burning, or accidental fruit thinning.
- Precision measurement: Use accurate measuring pipettes; never exceed label ppm dilution rates.
- Application timing: Apply during specific phenological windows (flowering, fruit set, or ripening) under cool, humid weather.
- Water quality: Use clean water with neutral pH to ensure chemical stability of hormone molecules.
- Safety: Wear personal protective equipment including gloves, goggles, and dust mask during dilution and spraying.
Official source
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Central Insecticides Board & Registration Committee ↗Related on KisanPe
Common questions
What is the difference between plant growth promoters and growth retardants?
Promoters (auxins, gibberellins, cytokinins) stimulate growth and fruit sizing, while retardants (paclobutrazol, chlormequat) curb excessive vegetative growth.
What is Ethephon used for in horticulture?
Ethephon breaks down into ethylene gas inside plant tissues, promoting uniform fruit ripening and color development.
Why must plant growth regulators be measured with extreme accuracy?
PGRs are active at tiny parts-per-million (ppm) levels; even slight overdosing can cause leaf burning, growth distortion, or fruit shedding.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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