Application of Phytohormones in Agriculture
Phytohormones are applied commercially in agriculture and horticulture: auxin for rooting powders and weedkillers, gibberellin for seedless fruit and malting, cytokinin for tissue culture, and ethylene for controlling fruit ripening.
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Applications by hormone
| Hormone | Agricultural application | How it works |
|---|---|---|
| Auxin | Rooting powder for stem cuttings | Stimulates root formation at the cut end, helping cuttings establish faster |
| Auxin | Selective weedkiller | A synthetic auxin applied in high concentration causes uncontrolled, damaging growth in broad-leaved weeds while leaving narrow-leaved crops largely unaffected |
| Gibberellin | Producing seedless fruit | Applied to unpollinated flowers, it stimulates fruit development without the need for fertilisation and seed formation |
| Gibberellin | Malting in the brewing industry | Speeds up seed germination, triggering enzymes that break down starch into sugar for fermentation |
| Cytokinin | Plant tissue culture | Promotes cell division and shoot formation, used to grow large numbers of identical plantlets from a small piece of tissue |
| Ethylene | Controlling fruit ripening | Applied to speed up ripening of fruit picked early for transport, or its build-up is limited in storage to slow ripening and extend shelf life |
Why these applications are useful
Commercial growers use phytohormones to make crop production more efficient and predictable: rooting powders speed up propagation, gibberellin allows growers to produce seedless fruit that consumers prefer, tissue culture using cytokinin allows rapid, large-scale production of disease-free planting material, and controlling ethylene lets fruit be transported unripe and ripened closer to the point of sale.
How it is examined
Questions usually describe a real agricultural practice, such as using rooting powder or producing seedless grapes, and ask you to identify which hormone is involved and explain how its known biological effect produces that practical outcome.
Worked exam-style question
Question. A gardener wants to grow a large number of new rose plants quickly from a single healthy parent plant. She takes stem cuttings, dips the cut ends in rooting powder, and plants them.
She also sprays a nearby field of broad-leaved weeds growing among cereal crops with a synthetic auxin. (a) Name the hormone in rooting powder and state its effect on the cutting.
(b) Explain why the synthetic auxin kills the broad-leaved weeds but leaves the cereal crop largely unharmed. (c) Cytokinin is used in tissue culture to produce new plants.
State one advantage of tissue culture over taking cuttings for producing new plants. (d) Suggest why the new plants produced from one parent by these methods are genetically identical to the parent.
Model answer. (a) The hormone is auxin; it stimulates root formation at the cut end, so the cutting develops roots faster and establishes itself. (b) The synthetic auxin is applied at a high concentration; broad-leaved weeds absorb it readily and respond with uncontrolled, excessive growth that disrupts their development and kills them, while narrow-leaved cereals absorb far less and are largely unaffected, so the weeds are targeted selectively.
(c) Any one: tissue culture can produce a very large number of plantlets from a small piece of tissue; the plantlets are free of disease; production is rapid and takes little space. (d) All the new plants are produced by mitosis (asexual reproduction) from the cells of one parent, with no fusion of gametes, so they carry the same genes as the parent.
Practice question
Try this. A fruit grower picks bananas while they are still green and firm, transports them a long distance, and then exposes them to ethylene gas shortly before selling them. Explain how this use of ethylene benefits the grower.
Exam tip
Key terms
Use these terms to explain how each application works:
- Hormone, a chemical messenger that controls a plant process in small amounts.
- Auxin, the hormone used in rooting powders and selective weedkillers.
- Germination, the process gibberellin speeds up in malting.
- Phototropism, a growth response controlled by auxin.
- Geotropism, the root and shoot growth response also controlled by auxin.
Source:SRC-DSKP-EN
Frequently asked questions
How is auxin used as a weedkiller?
How does gibberellin help produce seedless fruit?
Why is a synthetic auxin, rather than a natural one, usually used as a weedkiller?
How does tissue culture using cytokinin help produce disease-free crops on a large scale?
More for Responses in Plants
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