Plant Growth–Promoting Compounds (PGRs) as Bio-Stimulants in Crop Plants (By Prachi)
Plant Growth Regulators (PGRs) are low-concentration organic compounds that profoundly influence plant physiological and biochemical processes. When used as bio-stimulants, PGRs enhance stress tolerance, growth efficiency, yield stability, and quality, particularly under adverse environmental conditions such as drought, salinity, heat, and nutrient stress.
Among the most important PGR-based bio-stimulants are brassinosteroids, gibberellins, cytokinins, along with auxins, ethylene inhibitors, salicylic acid, and jasmonates.
1. Brassinosteroids (BRs)
Role in Stress Tolerance
Enhance cell elongation and division
Improve photosynthetic efficiency
Activate antioxidant enzymes (SOD, CAT, POD)
Increase tolerance to drought, salinity, heat, and heavy metals
Field Application
Mode: Foliar spray (preferred)
Stage: Vegetative stage, pre-flowering, or stress onset
Frequency: 1–2 sprays at 10–15 day interval
Recommended Dosage
0.1–0.5 ppm (very low dose; overdosing is harmful)
Example:
0.1 mg brassinolide in 1 liter of water
Crops Commonly Treated
Rice, wheat, maize
Cotton
Vegetables (tomato, chilli)
Oilseeds
2. Gibberellins (GA₃)
Role in Stress Tolerance and Growth
Promotes cell elongation
Breaks seed dormancy
Improves flowering and fruit set
Enhances tolerance to cold and moisture stress
Field Application
Mode: Foliar spray / seed soaking
Stage:
Seedling stage
Flower initiation
Early fruit development
Recommended Dosage
10–50 ppm (foliar spray)
50–100 ppm (seed soaking for 8–12 h)
Special Uses
Increase berry size in grapes
Improve malting quality in barley
Enhance panicle exertion in rice
3. Cytokinins (Kinetin, BAP, Zeatin)
Role in Stress Tolerance
Delay leaf senescence
Maintain chlorophyll stability
Improve sink–source relationship
Enhance tolerance to heat and nutrient stress
Field Application
Mode: Foliar spray
Stage:
Vegetative stage
Grain filling / pod development
Recommended Dosage
5–20 ppm
Often used in combination with micronutrients or amino acids
Benefits Observed in Fields
Better grain filling
Higher harvest index
Improved stay-green trait
4. Other Important PGRs Used as Bio-Stimulants
Auxins (IAA, IBA, NAA)
Root initiation
Stress recovery after transplanting
Used mainly for rooting and transplant shock reduction
Salicylic Acid
Activates systemic acquired resistance (SAR)
Enhances drought and pathogen tolerance
Jasmonic Acid / Methyl Jasmonate
Improves biotic stress resistance
Enhances secondary metabolite production
Precautions While Handling and Applying PGRs
Always use recommended doses
Overdose may cause phytotoxicity, flower drop, or abnormal growth.
Use clean water
Avoid alkaline or hard water.
Spray during cooler hours
Early morning or late evening.
Avoid mixing incompatible chemicals
Do not mix with strong pesticides unless compatibility is known.
Protective measures
Gloves, mask, and eye protection during preparation and spraying.
Uniform spray coverage
Fine mist spray preferred.
Avoid windy conditions
Prevent drift and uneven application.
Popular Plant Growth Regulators Available in the Market
| PGR / Active Ingredient | Commercial Product (India) | Major Application | Recommended Dose |
|---|---|---|---|
| Brassinolide | Brassinolide 0.1% SP | Stress tolerance, yield improvement | 0.1–0.5 ppm |
| Gibberellic acid (GA₃) | GA₃ 0.001% L / GA₃ tablets | Flowering, fruit size, elongation | 10–50 ppm |
| NAA | eg: Plano**fix | Flower drop control, fruit set | 10–20 ppm |
| Cytokinin (BAP) | Cyto**zyme / Bio**zyme | Delay senescence, grain filling | 5–20 ppm |
| Salicylic Acid | SA formulations | Stress and disease resistance | 50–100 ppm |
| Seaweed + PGR mix | Kel**pak, Sagar**ika | Growth + stress tolerance | As per the label |
| Auxins (IBA) | Root**ex | Root initiation | 500–1000 ppm (dipping) |
Field-Level Impact of PGR-Based Bio-Stimulants
10–25% yield improvement
Better performance under abiotic stress
Reduced dependence on chemical fertilisers
Improved economic returns for farmers
Suitable for integrated and sustainable agriculture
