Growth substances applications in agri-horticulture | Botany Optional for UPSC PDF Download

Introduction

The use of growth regulators in horticultural crops is a crucial aspect of modern agriculture. These regulators, also known as plant growth regulators (PGRs), play a significant role in enhancing crop production, improving fruit quality, and manipulating various growth processes in plants. This article delves into the multifaceted applications of growth regulators in horticultural crops, exploring their role in propagation, seed germination, induction of flowering, sex expression, flower and fruit thinning, pre-harvest drop prevention, fruit development, early maturity, ripening, delayed maturity, bud sprouting, and breaking dormancy. It also provides key definitions related to pruning techniques commonly used in horticulture.

Use of Growth Regulators in Horticultural Crops

1. Propagation

Propagation is a fundamental process in horticulture, and growth regulators are employed to facilitate it effectively. Growth regulators are applied in the form of paste and solution, with the concentration varying depending on plant species, types of cuttings, and the method of application. For rooting in stem cuttings, especially those that are hard to root, IAA (Indole-3-acetic acid), IBA (Indole-3-butyric acid), and NAA (1-Naphthaleneacetic acid) are commonly used.
There are two primary methods of application:

• Soak Method: 10 to 100 ppm for 12 -24 hrs called soak method. 
• Quick Dip Method: 1000to 5000 ppm for 5 seconds. Some G.R are used in layering, grafting and budding for getting high success.

These growth regulators are also utilized in layering, grafting, and budding to enhance the success rate.

2. Seed Germination

Gibberellic acid (GA) is known to significantly accelerate seed germination in many plant species. Pre-soaking seeds with GA, such as in crops like okra (bhendi) and sugar beet, can substantially increase germination rates.

3. Induction of Flowering

Plant growth regulators like NAA (1-Naphthaleneacetic acid) at concentrations of 10 to 50 ppm can induce early flowering in pineapple plants. Additionally, 2, 4-Dichlorophenoxyacetic acid (2,4-D) at 6 to 10 ppm is employed to induce flowering in pineapple. Conversely, flowering can be delayed by 1 to 2 weeks through the application of NAA at 200 to 800 ppm in crops such as apple, cherries, pears, peaches, and plums.

4. Sex Expression

Growth regulators have the unique ability to influence the sex of flowers. Male sterility can be induced in corn by using malic hydrazide (MH). Furthermore, the application of NAA, IAA, and GA at concentrations of 50 to 100 ppm can increase the production of female flowers in crops like pumpkin and cucumber, ultimately leading to higher yields.

5. Flower and Fruit Thinning

Many fruit trees exhibit alternating patterns of heavy and light fruiting from one year to the next. Growth regulators help maintain normal fruit production levels. NAA at concentrations of 5 to 10 ppm and NAA at 5 to 7 ppm are commonly used for thinning in crops like apple, peaches, and grapes.

6. Pre-Harvest Drop of Fruits

The issue of flower and fruit drop is a common concern in fruit crops. By applying NAA at concentrations of 10 to 50 ppm in crops like mango, citrus, and chilies, it is possible to reduce fruit drop by preventing the formation of the abscission layer.

7. Fruit Development

In grapes, the application of GA at concentrations of 50 to 100 ppm can lead to an increase in berry size, enhancing fruit development.

8. Early Maturity

Early maturity is often advantageous in the market, fetching higher prices. For instance, in pineapple cultivation, the application of 20 ppm NAA can induce early flowering and maturity by up to two months. Conversely, spraying 50 ppm NAA reduces maturity in grapes, while the use of 250 to 400 ppm Ethrel can induce early maturity in ber (Indian jujube).

9. Early Ripening and Colour Development

Fruits like mango, banana, and papaya typically ripen after harvest. Dipping these fruits in a 20-50 ppm Ethrel solution can induce a golden yellow color and accelerate the ripening process.

10. Delayed Maturity

When fruits need to be transported long distances, delaying ripening is essential. Dipping fruits in substances like 2,4-Dichlorophenoxyacetic acid (2,4-D), 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T), or malic hydrazide (MH-40) can extend the storage life of fruits.

11. Sprouting of Buds

Growth regulators such as Ethrel, GA, thio urea, IBA (Indole-3-butyric acid), and cytokinins are used to induce bud sprouting in various horticultural crops.

12. Breaking of Dormancy

GA, Ethrel, and NA are employed to break dormancy in seeds and buds, promoting the growth of new plants.

Key Definitions

• Bulk Pruning: Removal of large limbs, as opposed to the removal of a larger number of small branches.
• Crotch: The angle made by the attachment of a branch to the trunk.
• Deheading: The severe reduction of major limbs of a tree.
• Fine Pruning: Removal of small branches or twigs across the entire plant, as opposed to removing entire limbs.
• Heading Back: The removal of a significant amount of wood from the plant, which can be either coarse or fine.
• Leader: The most prominent and upright branch at the center of the tree that dominates all others.
• Pruning: The removal of plant parts to increase the value of the remaining parts.
• Scaffold Branch: The main branches arising directly from the trunk of the tree.
• Secondary Branches: The main branches arising from the primary or scaffold branches.
• Shoots: New growth on plants that bear leaves.
• Spur: A shoot or twig with limited growth.
• Thinning Out: Removal of an entire twig or branch at its point of origin.
• Modification of Form or Shape by Pruning: Altering the shape or form of a plant through pruning techniques.
• Trunk: The main axis of the plant extending from ground level to the point of branching.
• Water Sprout: A vigorous shoot that arises from dormant buds on the main scaffold branches, the leader, or near large pruning wounds.

Conclusion

In conclusion, the judicious use of growth regulators is essential for horticultural success. These substances offer a wide range of applications, from improving propagation to influencing flowering, fruit development, and ripening. Understanding the intricacies of growth regulators and their various applications is crucial for modern horticulturists striving for optimal crop yield and quality.