# Commercial Use of Plant Hormones - Plant hormones control **growth and development** in plants, making them valuable tools for commercial agriculture and horticulture - Farmers, growers and agricultural businesses use these hormones to **benefit commercial plant growing** in various ways - The main commercial applications include: - Selective weed killers - Rooting powders - Control of ripening - Production of seedless fruits - Prevention of premature fruit drop

Commercial plant hormones are naturally occurring or synthetic growth regulators used to manipulate plant growth for agricultural and horticultural benefit

## Selective Weed Killers - Auxins normally **promote growth** in plants - At **very high concentrations** (around 100 times greater than natural levels), auxins cause such rapid, uncontrolled growth that plant tissues become **distorted and damaged** - Root systems become twisted and deformed - Cell walls rupture and break down - Damaged tissues allow **pathogens to enter** the plant more easily - **Synthetic auxins** are manufactured and applied at these high concentrations to act as herbicides ### Auxin Concentration and Plant Response - The effect of auxin on plants depends heavily on concentration - This concentration-dependent response explains why the same hormone can both **promote growth** (rooting powders) and **kill plants** (herbicides)

- Low concentrations (0.01-0.1x natural): **Enhanced root growth** - basis for rooting powders - Natural concentrations (1x): **Normal, healthy growth** - High concentrations (10x): **Growth inhibition** - Very high concentrations (100x): **Tissue damage and death** - basis for selective herbicides ### Selective herbicides - These treatments are particularly effective as **selective weed killers** in agricultural settings - Work well in cereal crop fields (wheat, barley, oats) - Effective in maintaining grass lawns - **Grasses are significantly less sensitive** to these synthetic auxins than broadleaved plants - Grasses remain healthy while broadleaved weeds die - This allows crops like wheat to flourish while dandelions and docks are eliminated

Selective herbicides exploit the differential sensitivity between monocot grasses and dicot broadleaved plants to auxin concentrations

### Examples of use | Application | Target | Result | |-------------|--------|--------| | Wheat fields | Broadleaved weeds (e.g. thistles, poppies) | Wheat unaffected, weeds killed | | Barley cultivation | Dicot weeds | Clean cereal crop | | Garden lawns | Broadleaved weeds (e.g. clover, dandelions) | Uniform grass maintained | ## Rooting Powders - At **low doses**, auxins stimulate cuttings to **grow new roots** - These auxins are sold commercially in powder or gel form as **rooting compounds** - The preparation contains the correct dosage of auxin for optimal root development ### Application method 1. The lower end of the plant cutting is dipped into the rooting powder 2. The cutting is planted in compost or growing medium 3. With appropriate environmental conditions (humidity, temperature, light), **roots begin to form** within days to weeks 4. Once established, the cutting develops into a complete plant genetically identical to the parent ### Commercial applications - **Florist businesses** use this technique extensively - Propagating ornamental plants like roses and chrysanthemums - Creating uniform stock from prize specimens - **Nurseries** produce large numbers of plants from limited parent stock - Cost-effective plant production - Maintains desirable characteristics - **Home gardeners** can successfully propagate their own plants - Taking cuttings from geraniums, fuchsias, lavender - Growing replacement plants without purchasing seeds

Incorrect auxin concentration in rooting compounds can inhibit rather than promote root development

## Control of Ripening - The plant hormone **ethene** stimulates fruit to ripen - Ethene production increases as fruits mature naturally on the plant - Commercial growers exploit this to control **when and where** fruits ripen ### The challenge with delicate fruits - Some fruits become **soft and delicate** when ripe - Bananas develop soft flesh easily damaged by handling - Tomatoes become prone to bruising and splitting - Avocados soften and spoil quickly - Ripe fruits are **easily damaged during transport** - Long-distance shipping causes bruising - Stacking in containers crushes soft fruits - Temperature fluctuations accelerate spoilage ### Commercial solution using ethene 1. Fruits are **harvested when unripe** - Firm texture withstands handling - Can be stacked without damage - Extended shelf life during transport 2. Unripe fruits are **transported** to distribution centres or retailers - May travel thousands of kilometres - Stored in temperature-controlled containers 3. Fruits are **ripened artificially** using ethene gas - Applied during transport in specialized containers - Applied at destination warehouses - Controlled ripening chambers expose fruits to ethene 4. Fruits reach shops and consumers in **perfect ripe condition** ### Examples - **Bananas** picked green in tropical regions, ripened yellow near retailers - **Tomatoes** harvested firm, exposed to ethene before appearing on supermarket shelves - **Avocados** shipped hard, ripened using ethene to achieve creamy texture

Ethene gas treatment allows precise timing of when fruits reach peak ripeness, reducing waste and ensuring consistent quality

## Other Commercial Uses ### Production of seedless (parthenocarpic) fruits - **Auxins and gibberellins** can be applied to unpollinated flowers to make them develop into fruits - Normally, fruit development only occurs **after pollination and fertilisation** - Hormone application **bypasses this requirement** - Results in fruits that form **without seeds** (parthenocarpic fruits) | Fruit type | Advantage of seedless variety | |-------------|------------------------------| | Grapes | Easier to eat, preferred by consumers | | Watermelons | No interruption when eating, more edible flesh | | Citrus fruits | Convenient for juice production | - These seedless varieties often **command premium prices** in supermarkets - Consumers prefer seedless options for convenience ### Prevention of premature fruit drop - Some fruit trees naturally **drop fruit before harvest** (fruit abscission) - Strong winds trigger fruit drop - Natural thinning as trees shed excess fruit - Stress responses cause premature falling - Fruit that falls to the ground becomes **unusable** - Impact causes bruising - Contact with soil introduces decay organisms - Fruit rots quickly on the ground - **Auxin sprays** can be applied to fruit trees to prevent this - Strengthens the attachment point (abscission zone) - Delays natural fruit drop - Allows all fruit to be harvested at optimal time - Particularly valuable for commercial orchards growing: - Apples - Pears - Citrus fruits

Timing auxin application correctly maximizes harvest yield by keeping fruit attached until growers are ready to pick

## Summary of Commercial Plant Hormone Applications | Hormone | Commercial use | Benefit | |---------|---------------|---------| | Synthetic auxins (high concentration) | Selective weed killers | Eliminates broadleaved weeds without harming grass or cereal crops | | Auxins (low concentration) | Rooting powders | Promotes root growth in cuttings for plant propagation | | Ethene | Ripening control | Allows transport of unripe fruit and controlled ripening at destination | | Auxins + Gibberellins | Seedless fruit production | Creates parthenocarpic fruits preferred by consumers | | Auxins | Prevent fruit drop | Maintains fruit on trees until harvest time, reducing waste | - These applications demonstrate how **understanding plant biology** translates to practical agricultural benefits - Hormone use increases crop yields, reduces losses, and improves product quality - Modern agriculture depends heavily on these hormone-based technologies