Importance of Bio-regulators in Horticultural Crops

Introduction

• The growth and development of horticultural crops are controlled by hormones, also called plant growth substances or bio-regulators.
  These naturally occurring or synthetic compounds influence cell division, elongation, flowering, fruiting, ripening, and dormancy.
• Their judicious use in horticultural crops improves growth, yield, quality, and marketability.

Definition

• Bio-regulators (or Plant Growth Regulators – PGRs) are organic compounds, other than nutrients, which in small quantities influence the physiological processes of plants such as growth, differentiation, and development.
• They can be:
• Naturally produced (plant hormones)
• Synthetic chemicals that mimic or inhibit natural hormones.

Classification of Bio-regulators

Major Functions of Bio-regulators in Horticultural Crops

Vegetative Growth Regulation

• Auxins promote cell elongation and root initiation: e.g., IBA (2000 ppm) for rooting of guava, grapes, and pomegranate cuttings.
• Gibberellins (GA₃) stimulate stem elongation and leaf expansion.
• Cytokinins promote cell division and shoot proliferation.
• Growth retardants (CCC, paclobutrazol) reduce excessive vegetative growth (e.g., in mango, citrus).

Flower Induction and Regulation

• Gibberellins (GA₃) induce flowering in non-flowering plants (e.g., pineapple).
• Paclobutrazol (PP333) promotes flowering by reducing vegetative growth in mango and citrus.
• Ethephon (Ethrel) induces flowering in pineapple (50–100 ppm).
• Cytokinins help in bud break and synchronization of flowering.

Fruit Set and Fruit Development

• Auxins (NAA, 2,4-D) induce parthenocarpic (seedless) fruit set in tomato, citrus, and grapes.
• GA₃ (25–50 ppm) increases fruit set and berry size in grapes.
• NAA (20–40 ppm) improves fruit retention and reduces premature fruit drop in mango and citrus.

Fruit Thinning and Sizing

• NAA (10–20 ppm) and 2,4-D (10 ppm) used for fruit thinning in apple and citrus to improve size and quality.
• GA₃ (50–100 ppm) increases fruit length and weight in grape, apple, and citrus.

Fruit Ripening and Degreening: Ethrel (100–500 ppm) releases ethylene, which promotes: Uniform ripening in banana, mango, and pineapple. Degreening in citrus fruits for better market appearance.

Delay in Ripening (Postharvest Management)

• Cytokinins (BA, kinetin) delay senescence and maintain green color of leaves and fruits.
• GA₃ delays ripening in banana and tomato, extending shelf life.

Breaking Dormancy

• Gibberellins (GA₃, 100 ppm) break bud dormancy in grapes, peach, and potato tubers.
• Thiourea and KNO₃ are also used as dormancy-breaking agents in temperate fruits.

Prevention of Premature Fruit Drop

• NAA (20–40 ppm) or 2,4-D (10 ppm) applied before harvesting prevent fruit drop in mango, citrus, and apple.

Rooting of Cuttings and Grafting Success

• IBA (2000 ppm) and NAA (500–1000 ppm) promote rooting in hardwood and semi-hardwood cuttings.
• Improves survival rate in propagation of guava, grapes, pomegranate, and rose.

Parthenocarpy Induction

• Auxins (NAA), Gibberellins (GA₃), and 2,4-D induce seedless fruit formation.
• Example: GA₃ induces parthenocarpy in grapes and cucumber; NAA in citrus.

Color Development and Quality Improvement

• Ethrel enhances fruit color (degreening).
• Cytokinins and GA₃ improve size, sweetness, and shelf life of fruits.
• Calcium sprays with PGRs improve firmness and reduce cracking.

Postharvest Life Extension

• Cytokinins delay leaf yellowing and fruit aging.
• GA₃ maintains firmness and delays softening.
• Ethrel regulates uniform ripening for market preparation.

Role of Bio-regulators in Different Horticultural Crops

Methods of Application of Bio-regulators

Advantages of Using Bio-regulators