Because phytohormones control growth, ripening and dormancy, they are widely used in agriculture and horticulture. Growers apply natural hormones or cheaper synthetic versions to obtain earlier harvests, larger yields and produce of better quality.
Uses of auxin
- Rooting powder — synthetic auxin (such as IBA or NAA) is dusted on the cut ends of stem cuttings to stimulate the growth of adventitious roots, so cuttings root quickly.
- Selective weedkillers — auxin-based herbicides such as 2,4-D make broad-leaved weeds grow uncontrollably and die, while leaving narrow-leaved cereal crops unharmed.
- Preventing fruit drop — spraying auxin keeps fruits on the tree until they are ready for harvest.
- Producing seedless fruits — auxin sprayed on unpollinated flowers can cause fruit to develop without seeds (parthenocarpy).
Uses of other hormones
- Ethylene — used to ripen fruits such as bananas and mangoes evenly after they have been picked and transported while unripe.
- Gibberellin — sprayed to break dormancy and encourage uniform germination, to make grapes larger, and to increase stem length.
- Cytokinin — used to delay yellowing and keep leafy vegetables and cut flowers fresh for longer.
Example
Bananas are harvested and shipped while green and hard. At the destination they are exposed to a little ethylene gas in a ripening room so that a whole batch ripens together, ready for sale.
Key idea
The same hormone can be used in different ways: auxin roots cuttings at high concentration in weedkillers but prevents fruit drop at low concentration. The effect depends on the concentration and the plant part.
Benefits and cautions
Hormone treatments increase efficiency and reduce waste, but overuse of synthetic hormones can leave residues on food and harm the environment, so they must be applied at the correct concentration.
Remember
Auxin: rooting powder, weedkiller, seedless fruit, preventing fruit drop. Ethylene: ripening. Gibberellin: germination and larger fruits. Cytokinin: keeping produce fresh.