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Plant growth regulators (PGRs) are substances that are used to regulate plant growth in ways like boosting branching, limiting shoot growth, increasing return bloom, eliminating surplus fruit and changing fruit maturity. The amount of chemical absorbed by the plant, tree vigour and age, dose, timing, cultivar and weather conditions before, during and after treatment all affect PGR efficacy.
Substances related to auxins, gibberellins and inhibitors of gibberellin production, cytokinins, abscisic acid and compounds altering the ethylene state are the five types of plant growth regulators. There are various products that prevent plant hormone biosynthesis (Apogee, Retain).
Plant Hormones
A hormone is a substance that regulates how organisms function and develop. These molecules are also important in plants, where they regulate growth, development and reproduction. Plant hormones are what they’re called. Plant hormones are made in certain parts of the plant, such as the leaves, stems, and roots, and then transferred to different parts of the plant to perform their functions. Plant hormones have four distinguishing properties. Endogenous nature, mobility, regulatory influence and extraordinary reaction are some of them.
Plant Growth Regulators
Plant Growth Regulators are modest, basic substances that plants create spontaneously to control their growth and development.
Characteristics
Plant growth regulators can be gases (ethylene), terpenes (gibberellic acid), or carotenoid derivatives with a variety of chemical compositions (abscisic acid). Plant growth compounds, phytohormones and plant hormones are other names for them. They are classed as follows based on their actions:
- Cell division, cell expansion, flowering, fruiting and seed development are all promoted by plant growth promoters. Auxins, gibberellins and cytokinins are examples
- Plant Growth Inhibitors — These compounds prevent plants from growing and encourage dormancy and abscission. Abscisic acid is a good example
Ethylene can act as a promoter or inhibitor, although it is primarily a Plant Growth Inhibitor.
The five groups of plant growth regulators used in fruit crops include
Auxins are growth-promoting chemicals that aid in the elongation of shoots, although they can impede the formation of lateral buds at excessive quantities. Auxins can be employed as herbicides in addition to being plant growth regulators (2, 4-D etc.). Naphthaleneacetic acid (NAA) is a synthetic auxin used in apple production to thin fruit and minimise fruit drop just before harvest.
Gibberellins (GA) are hormones that promote cell elongation, shoot growth and regulate dormancy. Apples have been treated with Promalin®/Perlan® (which contains GA4+7 and 6-benzyladenine) to increase fruit size and minimise russeting. To delay ripening, improve fruit firmness, and lengthen the harvest period in sweet cherries, ProGibb 40SB and Falgro (containing GA3) are employed. In sour cherries, gibberellins are employed to control flowering and prevent overproduction. Gibberellin biosynthesis is inhibited by Apogee or Kudos 27.5 WDG® (Prohexidione-calcium). Apogee or Kudos 27.5 WDG are used to limit runner production in strawberries and affect the shape of trees (apple and cherries).
Cytokinin’s are hormones that encourage cell division. Branching and bud initiation are both aided by cytokinin’s. They’re utilised in apples as fruit thinners (Maxcel® or Cilis Plus® 6-BA).
Abscisic acid regulates water loss from plants by controlling the dormancy of buds and seeds. It also limits shoot growth.
Ethylene stimulates the abscission of leaves and fruits, limits shoot elongation, and prevents the growth of lateral buds. Ethylene is involved in the transition of fruit from physiological maturity to ripeness in apples and cherries. Ethephon (Ethrel®) is a synthetic chemical that when applied releases ethylene. Retain inhibits ethylene biosynthesis, allowing fruit to hang on trees over longer periods of time and extending storage life.
Plant Hormones vs. Plant Growth Regulators: A Comparison
| Plant Hormones | Plant Growth Regulators |
| Plant hormones and plant growth regulators are substances that regulate plant development and growth. Plant hormones are naturally occurring chemicals produced by plant metabolic processes. | Humans artificially create plant growth regulators for use in agriculture and floriculture. Plant growth regulators operate similarly to natural plant hormones. Plant hormones, on the other hand, are natural, whereas plant growth regulators are synthetic. |
Conclusion
Plant growth regulators are substances created artificially by humans to control the growth and development of plants. These compounds function as plant hormones. As a result, they’re also known as exogenous plant hormones. Agriculture, horticulture, and floriculture all use plant growth regulators. They are used in low concentrations and pose no danger to humans or animals. Plant growth regulators, on the other hand, should be used in the correct concentrations; misuse can have a negative impact on food harvest yield and quality.
Plant growth regulators are often given as foliar sprays or soil drench solutions. Plant growth regulators, unlike natural plant hormones, have a short-term effect and must be reapplied to attain the desired effect.
