10 min readPlant growth regulators (PGRs) are natural or synthetic compounds that, in very small amounts, promote, inhibit or modify plant growth and development. The five main classes are auxins, gibberellins, cytokinins, abscisic acid and ethylene. Growers use them for rooting, flowering, fruit set, ripening and height control. In India, PGRs are regulated under the Insecticides Act, while biostimulants come under the Fertiliser Control Order.
What are plant growth regulators?
TNAU defines plant growth regulators as organic compounds, active at very low concentrations, that promote, inhibit or modify growth and development. The naturally occurring ones inside plants are called plant hormones; the synthetic ones are called growth regulators. A plant hormone is made in one part of the plant and moved to another, where a tiny amount causes a response.
In practice, a grower buys a PGR to change timing or shape: root a cutting faster, hold flowers on the plant, set fruit without seeds, ripen fruit on a schedule, or keep a plant short and compact. A PGR changes how the plant uses what it has; it does not replace water, nutrients or pest control.
What are the main types of plant growth regulators?
TNAU lists ten broad groups, but five classes cover almost every question: auxins, gibberellins, cytokinins, abscisic acid and ethylene. The first three are promoters; abscisic acid and ethylene are inhibitors.
| Class | What it does | Natural example | Synthetic or applied example | Typical agricultural use (TNAU) |
|---|---|---|---|---|
| Auxin | Stimulates cell elongation and division; roots cuttings; delays fruit drop | IAA (main natural auxin), IBA, PAA | NAA, 2,4-D, IBA | Rooting of cuttings (10 to 1,000 ppm), preventing premature leaf, flower and fruit fall, pineapple flowering, parthenocarpic fruit, tissue culture (source) |
| Gibberellin | Elongates shoots, breaks dormancy, promotes flowering and fruit set | GA3 (from the fungus Gibberella fujikuroi) | Gibberellic acid (GA3) formulations | Seedless grape fruit set, taller nursery seedlings, breaking seed and bud dormancy (source) |
| Cytokinin | Cell division, delays senescence, overcomes apical dominance | Zeatin (first isolated from maize) | Kinetin, benzyladenine | Tissue culture, delayed ageing, parthenocarpy, flower and fruit development (source) |
| Abscisic acid (ABA) | Inhibitor; promotes dormancy and stress response | ABA, phaseic acid (called dormins) | Few field products | Mostly physiological role; classed as an inhibitor |
| Ethylene | Inhibitor; ripening, leaf shedding, breaks dormancy | Ethylene gas made by plants | Ethephon (Ethrel, CEPA) releases ethylene | Ripening of mango, banana, citrus, papaya; abscission (source) |
Beyond these five, TNAU lists synthetic growth retardants (CCC, AMO-1618, Phosphon-D and others) and miscellaneous synthetic substances, including synthetic auxins and cytokinins. Growth stimulants such as brassinolide are also sold.
What are natural and synthetic plant growth regulators?
- Natural (endogenous): made by the plant itself. IAA, GA3, zeatin, ABA and ethylene are examples.
- Synthetic: made by industry to behave like the natural ones or to block them. NAA, 2,4-D, ethephon, paclobutrazol, chlormequat and mepiquat chloride are examples.
- Extract-based products: seaweed extracts and similar products contain small amounts of natural hormones along with nutrients. In India these are usually classed as biostimulants (see below), not as PGRs.
What are the top plant growth regulators used in agriculture?
There is no official "top 10", but TNAU's list of marketed plant growth regulants gives a clear picture of the active ingredients in common use. The table pairs each with what it is used for.
| Active ingredient | Class | Marketed example in TNAU list | Crops in that list | Katyayani product page |
|---|---|---|---|---|
| NAA (1-naphthyl acetic acid) 45 g/l | Auxin | Planofix (Bayer) | Apple, pear, pineapple | NAA 4.5% SL |
| IBA (indole butyric acid) | Auxin | Seradix B (Bayer) | Ornamentals (cuttings) | Rooting hormone |
| Gibberellins (GA3) | Gibberellin | ProGibb 4% (Valent) | Grape, pear, citrus, potato, mango | Accel-Gro GA3 40% WSG |
| 6-benzyl adenine + gibberellins | Cytokinin + GA | Promalin (Valent) | Apple, plum, flowers | - |
| Ethephon 480 g/l | Ethylene releaser | Ethrel (Bayer) | Apple, citrus, cotton, grape, maize, sugarcane and others | Ether-39 ethephon |
| Paclobutrazol 250 g/l | Growth retardant | Cultar (Syngenta) | Litchi, mango, peach, plum | Fast paclobutrazol 23% SC |
| Mepiquat chloride 50 g/l | Growth inhibitor | Pix (BASF) | Cotton | - |
| Chlormequat chloride 750 g/l | Growth inhibitor | CeCeCe 750 (BASF) | Pear, wheat | - |
| Daminozide 850 g/kg | Growth retardant | B-Nine (Crompton) | Flowers, ornamentals | - |
| Thidiazuron/diuron | Defoliant | Dropp Ultra (Bayer) | Cotton | - |
| Brassinolide 0.1% | Growth stimulator | Double (Godrej) | Agricultural and horticultural crops | Bloom Booster homobrassinolide |
Katyayani also lists forchlorfenuron 0.1% (CPPU) and triacontanol 0.1% EW. TNAU's crop table notes triacontanol with kinetin and GA3 at 1,000 ppm in rice for grain filling and delayed senescence. For the whole range see the plant growth regulator collection; papaya growers with poor flowering can start with PGRs for papaya flowering.
What are PGRs used for? Uses by crop
The TNAU crop table is research-based and gives doses as ppm. Use it to understand what each PGR does, and take the actual dose from the registered label for your product, crop and stage.
| Crop | PGR (TNAU) | Effect reported |
|---|---|---|
| Rice | Kinetin, GA3 and triacontanol (1,000 ppm) | Grain filling and partitioning; delayed senescence |
| Cotton | IAA, NAA (30 ppm), CCC | Less boll shedding; more bolls, boll weight and lint yield |
| Groundnut | Mepiquat chloride (125 ppm) | Higher grain yield and chlorophyll synthesis |
| Sugarcane | Ethephon, glyphosine | Slower growth rate and regulated ripening |
| Mango | Ethephon (1,000 ppm) | Accelerated fruit ripening and better surface colour |
| Banana | Ethrel (1,000 ppm) | Ripening about two days earlier |
| Papaya | Ethephon + NaOH (2,000 ppm) | Ripening within 24 hours |
| Thompson Seedless grape | GA3 (25 ppm), cluster dip at calyptra falling | Increased fruit set |
| Mandarin orange | 2,4-D (20 ppm) or NAA (100 ppm) at flowering | Increased fruit set |
| Coconut | 2,4-D (30 ppm) one month after spathe opens | Fruit set 32.5% vs 23% in control |
| Gourds (snake, bitter, bottle) | Ethrel (100 ppm), four times from 10-15 days after sowing | Increased yield |
Mango flowering is a special case. TNAU lists paclobutrazol (Cultar) for mango and litchi. An ICAR-IIHR trial in Bengaluru with Totapuri trees reported earlier flowering by 20 to 25 days and 30 to 65% more flowering when paclobutrazol was applied from late July to October, with the best yield (141.1 kg per plant, 55% above control) from 2.5 g active ingredient per plant in the last week of September. Doses vary by variety and canopy, so follow the label and your state advisory, and read our mango flower pests and diseases guide for what to protect once flowering starts.
How do you read ppm and apply PGRs safely?
PGR doses are tiny and the margin for error is small. TNAU explains units this way: 1 ppm is 1 mg dissolved in 1 litre; 1% is 1 g dissolved in 100 ml. So, by my arithmetic, 100 ppm is 100 mg per litre, or 1 g in 10 litres. Always dissolve the pure ingredient in a little water or solvent first, as the label says, then make up the volume.
- Use a registered product and read the label for crop, stage, dose and safety interval. Do not copy research ppm onto a different product.
- Match the stage. Most PGR effects depend on timing: rooting needs cuttings, fruit set needs flowering, ripening needs mature fruit.
- Never overdose. The ICAR-IIHR mango study found higher paclobutrazol rates caused shoot and panicle compaction and left soil residues for 9 months, against 5 to 6 months at the lower rate (ICAR record, search summary).
- Spray or apply evenly with clean water in the cooler part of the day, and do not mix with other products unless the label allows.
- Try a small area first if you are using a PGR on a crop for the first time.
- Wear gloves and a mask, store out of reach of children and follow the pre-harvest interval.
- Feed the crop. A PGR cannot fix a nutrient deficiency. Test first using your soil health card and check pH (soil pH and nutrient lock).
Which PGR for which problem?
| Problem | PGR class | Active ingredient (TNAU examples) | Note |
|---|---|---|---|
| Cuttings not rooting | Auxin | IBA, NAA (10 to 1,000 ppm range for rooting) | Dip base of cutting |
| Flower and fruit drop | Auxin | NAA, 2,4-D, IAA | TNAU: prevents premature leaf, fruit, flower fall; cotton boll shedding reduced with NAA 30 ppm |
| Poor fruit set in grapes | Gibberellin | GA3 25 ppm cluster dip | Timing at calyptra falling |
| Uneven flowering in pineapple | Auxin + ethylene | NAA (Planofix) and ethrel | Applied at the leaf stage in TNAU table |
| Fruit not ripening uniformly | Ethylene | Ethephon (mango 1,000 ppm; papaya 2,000 ppm with NaOH) | Post-harvest or pre-harvest per label |
| Excess vegetative growth, poor flowering | Retardant | Paclobutrazol (mango, litchi), mepiquat chloride (cotton, groundnut) | Residue and dose caution |
| Lodging in wheat | Retardant | Chlormequat chloride | Listed for pear and wheat |
What is the difference between PGRs and biostimulants?
This is the most confused pair in the trade. The difference is in the job and in the law.
| Feature | Plant growth regulator | Biostimulant |
|---|---|---|
| What it is | Hormone-like compound (natural or synthetic) that changes growth and development at very low doses | Substance or microorganism whose main job is to stimulate physiological processes, such as nutrient uptake or stress tolerance |
| Typical examples | NAA, GA3, ethephon, paclobutrazol, chlormequat | Seaweed extracts, protein hydrolysates and amino acids, humic and fulvic acids, vitamins, antioxidants, cell-free microbial products |
| Regulation in India | Insecticides Act, 1968; registered by CIB&RC | Fertiliser (Control) Order 1985, Clause 20C and Schedule VI, since notification S.O. 882(E) of 23 Feb 2021 |
| Legal status of a product | Needs CIB registration for a crop | Only products listed in Schedule VI can be made, imported or sold as biostimulants; provisional registrations ended 16 June 2025 |
| Effect | Strong, specific, dose-sensitive | Mild, broad, supports the plant |
| Risk of overdose damage | Higher | Lower, but not zero |
The Indian biostimulant definition specifically excludes pesticides and plant growth regulators. The EU draws the line by function: its regulation defines a plant biostimulant as a product that stimulates nutrition processes independently of its nutrient content, and says other growth regulators may still count as plant protection products. For the Indian rules in detail, including the 146 products in Schedule VI as of 9 Sep 2025 (a number that changes), read our guide to biostimulants in India under FCO. If you only need a mild, general growth aid, products like seaweed extract belong in the biostimulant bucket; confirm the category on the label.
What are common mistakes with PGRs?
- Treating a PGR as a fertiliser substitute and skipping nutrition and irrigation.
- Using the research ppm from a table on a product with a different concentration.
- Spraying at the wrong stage, for example GA3 after grape berries have set.
- Repeating sprays "to be sure". Overdose can compact shoots, distort leaves or delay harvest.
- Ignoring pre-harvest intervals and residue limits for export crops.
- Mixing with products that change pH or contain copper without checking the label.
Conclusion
Plant growth regulators are precise tools. Learn the five classes, match the class to the problem (auxin for rooting and drop, GA3 for fruit set, ethephon for ripening, retardants for shape), use a registered product at the label dose and stage, and keep nutrition and irrigation right. When you need a mild general stimulant rather than a hormone-type effect, the biostimulant category under FCO is the right place to look.
Why trust this guide
Written by Team Katyayani, Editorial Team at Katyayani Organics. Cross-checked against published research and university extension programs.
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