5.3 - Application of Phytohormones in Agriculture

• Phytohormones are involved in the development of flowers, fruits, stems and roots.
• They may occur naturally, be synthesised in a laboratory or be extracted for agricultural uses.

Commercial Uses of Phytohormones

• Auxin
  • Encourages crop growth.
  • Promotes root growth for asexual reproduction in woody stem cuttings of horticultural crops.
  • Produces seedless fruits through parthenocarpy.
  • Acts as a weed killer.
  • Induces dormancy in potatoes during storage or distribution.
  • Promotes growth of low-lying, lush plants.
• Gibberellin
  • Treats mutated dwarf plants so they grow to normal heights.
  • Promotes rapid elongation of flower stems.
  • Produces larger grapes.
  • Promotes germination of lettuce, oat and tobacco seeds at low temperatures and low light intensity.
• Cytokinin
  • Promotes cell division and differentiation in tissue culture.
  • Is used with auxin in tissue culture to form plant organs such as roots and stems.
  • Delays leaf senescence in newly cut flowers.
• Abscisic acid
  • Inhibits germination and growth.
• Ethylene
  • Promotes rapid and uniform fruit ripening commercially.
  • Promotes simultaneous flowering in field crops.

Effect of Ethylene on Fruit Ripening

• Problem statement: What is the effect of ethylene on tomatoes?
• Aim: Compare fruit ripening in the presence and absence of ethylene.
• Hypothesis: Tomatoes ripen faster in the presence of ethylene.
• Variables:
  • Manipulated: Presence of ethylene.
  • Responding: Ripening of tomatoes.
  • Constant: Type of fruit and temperature.
• Materials: Two paper bags, one ripe banana and two unripe tomatoes.
• Procedure:
  1. Label the paper bags A and B; record the initial colour and condition of both tomatoes.
  2. Place one unripe tomato in bag A.
  3. Place one unripe tomato and one ripe banana in bag B.
  4. Seal both bags.
  5. After 12 hours, compare the colour and hardness of both tomatoes.
• Expected result: The tomato in bag B ripens faster because the ripe banana releases ethylene, which stimulates fruit ripening.
• Conclusion: Tomatoes ripen faster in the presence of ethylene; the hypothesis is accepted.
• Use paper bags; plastic bags trap moisture and may cause fruit to spoil faster.