Use of Plant Growth Regulators in Agriculture

In agricultural application a PGR is defined as "a substance used for controlling or modifying plant growth processes without appreciable phytotoxic effect at the dosage applied." In order for a PGR to be registered by the U.S. Environmental Protection Agency, its use, as recommended on the label, must be safe for the plant, its applicator, and the environment as far as can be feasibly determined. Thus, neither plant nor human injury is to be expected from most properly applied PGRs (2).

The PGRs are divided into five general groups of compounds based on their chemical structures and effects on plants. The groups are auxins, gibberellins, cytokinins, ethylene, and a group called inhibitors, which includes abscisic acid, phenolics, and alkaloids. Some new PGRs do not fit neatly into these classifications but are described as having effects that resemble those for known PGRs. For example, cytokinin-like is a term used to describe new products extracted from seaweed products. A new PGR may be developed to counter the effects of a known plant hormone by interfering with natural plant hormone production. A general description of each growth regulator's effect on plant growth follows.

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