Plant Propagation and Nursery Management (1+1)

Introduction

Plant growth regulators (PGR) usually are defined as organic compounds, other than nutrients, that affect the physiological processes of growth and development in plants when applied in low concentration. Practically, plant growth regulators can be defined as either natural or synthetic compounds that are applied directly to a target plant to alter its life processes or its structure to improve quality, increase yields or to facilitate harvesting. The term plant hormone, when correctly used is restricted to naturally occurring plant substances. This fall into five classes: auxins, gibberellins, cytokinins, inhibitors and ethylene (gas). The term plant growth regulators include synthetic as well as naturally occurring hormones.
Main functions

Auxins: Cause enlargement of plant cell.
Giberellins: Stimulate cell division, cell elongation or both.
Cytokinins: Stimulate cell division in plants
Inhibitors: Plant hormones that inhibit or retard a physiological or biochemical process in plants.

Rooting and plant propagation

• One of the oldest uses of plant growth regulators has been to initiate or accelerate the rooting of cuttings .
• The best and most commonly used chemical for this purpose is indole butyric acid (IBA), which is decomposed relatively slowly by the auxin-destroying enzyme system in plants. Because this compound also moves very slowly in the plant, much of it is retained near the site of application.
• Another highly active auxin frequently used for root promotion is naphthalene acetic acid (NAA). As NAA is more toxic than IBA, there is a greater danger of injury to treated plants. The amides of both compounds are also effective rooting agents.
• Many phenoxy compounds, including 2,4-D, 2,4,5-T (trichlorophenoxy acetic acid) promote root formation if used at low concentrations. The type of root systems produced varies with the growth regulators used. These phenoxy acids tend to produce bushy, stunted and thickened roots systems.
• IBA is commercially used as rooting hormone in many horticultural and forest plants including apple, peach ,plum, poplar ,ficus, grapes, kiwifruit, pomegranate, rose, tea, winged bean, rhododendron, egg plant etc.