Question

Fruit and leaf drop at early stages can be prevented by the application of
A. Gibberellic acid
B. Cytokinins
C. Ethylene
D. Auxins

Answer 1

Hint:Plant Cell Growth regulators are plant hormones that play an important role in growth and differentiation of tissues and cultured cells. Various classes of plant growth regulators are used in culture media which are, Auxins, Cytokinins, IBA (Indole-3-Butyric Acid), Gibberellins, Abscisic acid, Ethylene, 6 BAP (6 Benzyl adenine), IAA (Indole Acetic Acid), Zeatin and trans Zeatin Riboside.

Complete answer:
You should know that Gibberellic acid (GA) is a hormone or growth-regulating chemical that is noticed in varying degrees in all parts of plants. GA is a natural occurring hormone, it stimulates both elongation and cell division and is used in manipulation of flowering and fruit development in crops.
Now let's discuss Cytokinins, this class of plant hormones comprises numerous aspects of plant growth, physiology and development( including cell division, chloroplast differentiation and delayed senescence).
Ethylene, is referred to as a multifunctional phytohormone that is regulating both growth, and senescence. Depending on its concentration, timing of application, and also the plant species, it inhibits or promotes growth and senescence processes.
Remember, Auxins first were isolated from human urine and are produced by growing tips of root and stem. Auxin promotes cell division and differentiation and prevents leaf and fruit drop at early stages. Auxin is important in promoting the abscission of older mature leaves and fruits.

Additional information:
Interestingly, the first phytohormone discovered was Auxin by the biologist Charles Darwin. Auxins are considered as one of the most important plant hormones.

Therefore, the correct option is option D

Note:- Always keep in mind, Auxin also plays a role in maintaining apical dominance. Majority of plants have lateral buds at nodes. Buds are embryonic meristems which are maintained in a dormant state. Auxin maintains this dormancy. Note that, as long as sufficient auxin is secreted by the apical meristem, the lateral buds are dormant. If we remove the apex of the shoot, the auxin will no longer be produced, this will cause the lateral buds to begin to grow and break their dormancy. As a result, the plant becomes bushier. When a gardener trims, they apply apical dominance.