PGR’s are compounds that effect root growth, flowering, stem elongation or
shortening. They can be either synthetic compounds that mimic the role of
natural hormones, or they can be hormones extracted from plant tissue.
PGR's, are applied as either a foliar spray or a liquid drench to the root
There are 5 groups of PGR's:
1. Auxins: These produce several growth responses in plants including the
formation of adventitious roots, promotion of apical dominance, flower
formation and fruit-set and growth. Common examples of auxins include NAA
(naphthyl-acetic-acid) and IBA (indole-butyric-acid). These are used to
stimulate root growth in cuttings.
2. Gibberellins: These are used to stimulate cell division and elongation.
They break seed dormancy and induce flowering. Gibberellic acid, for
example, can be used to influence the timing of flowering, flower gender
and flower size.
3. Cytokinins: These can be useful for stimulating cell division, inducing
shoots and delaying aging and death (senescence). Benzyl-amino-purine
(BA6) is a common cytokinin used for inducing side branching. This is
useful for the development of short, bushy plants.
4. Ethylene: Used for promoting ripening, inducing leaf drop (abscission)
and senescence. Ethylene is commonly used to ripen fruit in preparation
5. Abscisic Acid (ABA): This is a plant growth inhibitor. It causes
abscission of leaves, fruits and flowers and causes stomata to close.
During periods of drought when stomata are closed, high concentrations of ABA are found in leaf guard cells.