Production of Cucumber has increased manifold in recent years. Application of which of the following phytohormones has resulted in this increased yield as the hormone is known to produce female flowers in the plants:

Concept:

• Plant growth regulators (PGRs) also called phytohormones are small, simple molecules of different chemical compositions.
• There are two categories of PGRS: one that promotes growth, cell division, formation of flowers, fruits, seeds, etc., and other categories of PGRs promote wound healing and response to stress in plants.

Explanation:

Different plant growth regulators are:

• Auxins
  • Indole 2-Acetic Acid (IAA) is a type of Auxins.
  • Auxins help in root initiation in stem cuttings, promote flowering, and prevent fruit, and leaf drop in the early stages of plant growth.
• Gibberellins
  • The most common gibberellin used is Gibberellic acid (GA3).
  • They are used to increase the length of the axis (grapes), length of stem (sugarcane), elongation, and improvement in the shape of fruit (apple), and bolting (beetroot, cabbage). 
• Cytokinin
  • Natural cytokinin is synthesized in the sites of rapid cell division like root apex, shoot buds, and young fruits.
  • They help in overcoming apical dominance and delay in leaf senescence.
• Ethylene
  • It is a gaseous PGR. It plays a major role in the senescence and abscission of leaves and flowers.
  • It also helps in early fruit ripening.
  • Ethephon is commonly used ethylene it promotes female flowering in cucumber and helps in improving the yield.

So, the correct answer is option 4.