Plant Growth Regulators (PGRs): Functions, Benefits, and Best Practices for Modern Agriculture

What Are Plant Growth Regulators?

Plant Growth Regulators (PGRs) are natural or synthetic compounds that influence plant physiological processes such as rooting, flowering, fruit development, ripening, stress tolerance, and senescence. Unlike fertilizers, PGRs manage how plants grow, not what nutrients they receive.

They are widely used in:

• Field crops

• Orchards and vineyards

• Vegetables and greenhouse crops

• Turfgrass and landscaping

• Seedling nurseries and transplant production

When used properly, PGRs improve yield, uniformity, and crop quality while reducing production risks.

Major Categories of Plant Growth Regulators and Their Functions

Below are the most common PGR families, their mechanisms, and practical benefits.

1. Auxins: Rooting, Fruit Set, and Growth Direction

Auxins regulate cell elongation and root formation.

Key functions

• Stimulate root initiation and root hair development

• Reduce fruit drop before harvest

• Promote callus formation in cuttings

• Guide phototropism (plants growing toward light)

Typical products / active substances

• Indole-3-acetic acid (IAA)

• Indole-3-butyric acid (IBA)

• Naphthaleneacetic acid (NAA)

Common uses

• Rooting powders and solutions

• Preventing early fruit drop in citrus, mango, apple

• Improving transplant survival in vegetables and seedlings

2. Gibberellins (GA): Elongation, Flowering, and Fruit Size

Gibberellins stimulate cell elongation and reproductive development.

Key functions

• Increase stem elongation and internode growth

• Break seed dormancy

• Improve fruit size and shape

• Enhance malting quality in barley

Typical active ingredient

• Gibberellic acid (GA3)

Practical applications

• Bigger berries in grapes

• Uniform sprouting in seeds

• Delay aging in leafy vegetables

3. Cytokinins: Cell Division, Anti-Senescence, and Quality

Cytokinins promote cell division and delay leaf aging.

Benefits

• More branching and shoot development

• Greener leaves for longer (delayed yellowing)

• Better flower bud formation

• Improved fruit firmness and shelf life

Examples

• Kinetin

• Zeatin

• Benzylaminopurine (6-BAP)

Commonly used in vegetables, ornamentals, and nursery crops.

4. Ethylene and Ethylene Modulators: Ripening Control

Ethylene acts as a natural ripening hormone.

Ethylene uses

• Synchronize ripening in bananas, tomatoes, and mango

• Promote flowering in pineapple

• Accelerate senescence when needed

Ethylene inhibitors (anti-ethylene)

• Delay ripening

• Maintain firmness and freshness

• Extend storage and transport life

Useful in post-harvest handling, exporting fruit, and greenhouse operations.

5. Abscisic Acid (ABA): Stress Tolerance and Water Management

ABA plays a key role in abiotic stress management.

Main functions

• Promote stomatal closure to reduce water loss

• Improve drought and heat tolerance

• Enhance tolerance to salinity stress

• Improve seed dormancy regulation

Particularly valuable in arid, saline, and high-temperature regions.

Additional PGR Groups Commonly Used in Agriculture

To expand depth, here are more specialized PGR types widely applied in commercial farming.

6. Brassinosteroids

Stimulate growth and increase resistance to stress.

Benefits

• Stronger stems and shoots

• Improved photosynthesis efficiency

• Enhanced tolerance to drought, cold, and chemicals

• Better grain filling and fruit quality

7. Growth Retardants (Anti-GAs)

These prevent excessive elongation, creating compact plants.

Examples

• Paclobutrazol

• Chlormequat chloride (CCC)

• Daminozide

Uses

• Reduce lodging in cereals

• Control height in ornamentals and nursery plants

• Improve root development instead of leaf elongation

8. Flowering Inducers

Encourage flowering at specific times.

Benefits

• Synchronize flowering for uniform harvest

• Increase number of flowers

• Improve fruit setting efficiency

Widely used in mango, pineapple, and ornamental crops.

9. Root Growth Promoters

Often combinations of auxins, amino acids, humic acids, and biostimulants.

Key advantages

• Stronger early rooting

• Faster transplant recovery

• Better nutrient and water uptake

Ideal for seedlings, plug trays, and crops grown under stress.

10. Fruit Set and Fruit Enlargement Regulators

Used to ensure high-quality production.

Applications

• Improve pollination efficiency

• Reduce misshapen fruit

• Increase uniform size and smoothness

• Prevent premature fruit drop

Common in tomato, citrus, grapes, strawberry, apple, and watermelon.

Practical Examples by Crop

Vegetables

• Stronger seedlings and faster transplant recovery

• Higher fruit set in tomato, pepper, cucumber

• Better size uniformity for commercial markets

Fruit Trees

• Reduce fruit drop

• Improve color and sweetness

• Control flowering and ripening time

Field Crops (rice, wheat, corn)

• Reduce lodging

• Improve stress tolerance

• Support stronger roots and tillering

Greenhouse Crops

• Compact plants with stronger stems

• Controlled growth for limited space

• Uniform flowering and harvest timing

Best Practices for Using PGRs

• Always follow label instructions

• Avoid overdosing

• Apply at the right growth stage

• Test compatibility before tank mixing

• Conduct a small trial first

Correct timing and precision are critical for success.

Final Takeaway: PGRs as Strategic Tools for Modern Farming

Plant growth regulators are not "magic chemicals." They are precision tools that help farmers optimize growth, increase marketable yield, and manage stress when used responsibly.

Integrated into a balanced agronomy program, PGRs support:

• Higher productivity

• Consistent quality

• Better economic returns

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FAQ

1. Are plant growth regulators safe?

Yes, registered PGRs are considered safe when used according to government regulations and product labels. Overuse or unregistered materials may pose risks.

2. Do PGRs replace fertilizers?

No. Fertilizers supply nutrients.
PGRs regulate how plants grow and how efficiently they use nutrients. They work best together.

3. Can PGRs increase crop yield?

In many crops, yes. PGRs improve:

• Fruit set

• Root development

• Stress resistance

• Uniformity and quality

Yield results depend on crop, climate, timing, and management.

4. Are PGRs allowed in organic farming?

Some natural hormone-like substances and biostimulants may be allowed, but rules vary by country and certifying body. Always check certification guidelines.

5. Can overuse of PGRs damage crops?

Yes. Excessive application can cause:

• Leaf curling or burning

• Abnormal growth

• Flower abortion

• Reduced yield

Always respect recommended doses.

6. What is the best time to apply PGRs?

Common timing windows include:

• Seedling stage

• Vegetative growth

• Pre-flowering and flowering

• Early fruit set

Correct timing depends on the target effect.

7. Can I mix PGRs with pesticides or fertilizers?

Sometimes — but not always.
Avoid mixing unless compatibility is proven or recommended by the manufacturer. Conduct a jar test first.