Question

Which of the following hormones is used in root formation On stem cuttings? (a) Kinetin (b) GA (c) \(A B A\) (d) \(I B A\)

Short answer

The hormone used in root formation on stem cuttings is (d) IBA.

Step-by-step solution

Identify the Correct Hormone

To solve this exercise, we need to recall the function of each hormone listed and identify the one that is known to promote root formation in stem cuttings.

Eliminate the Incorrect Options

Kinetin is involved in promoting cell division, GA (gibberellins) is primarily involved in promoting stem elongation, and ABA (Abscisic acid) generally acts to inhibit growth and promote dormancy.

Select the Correct Answer

IBA (Indole-3-butyric acid) is the hormone that is commonly used to stimulate root formation on stem cuttings. Therefore, the correct answer is (d) IBA.

Key concepts

Indole-3-Butyric Acid (IBA)

Indole-3-butyric acid, or IBA, is a plant hormone in the auxin family that plays a vital role in the process of root formation, especially in the method of stem cutting propagation. When a stem cutting is taken, it lacks the roots necessary for the absorption of water and nutrients from the soil. IBA acts as a stimulant; it encourages the differentiation of cells at the cut end of the stem into root cells, leading to the formation of new roots.

In a horticultural context, IBA is often applied as a rooting powder or gel to the base of a cutting before it is placed into growing media. The hormone boosts root cell development so effectively that it's the go-to choice for many gardeners and commercial growers looking to clone plants efficiently. Since IBA is a synthetic auxin, it mimics the plant's natural growth hormones, seamlessly integrating into the plant's growth process without harming it, provided it is used in appropriate concentrations.

Plant Auxins

The term 'auxins' refers to a class of plant hormones that regulate various aspects of growth and development. Auxins, which include hormones like IBA and indole-3-acetic acid (IAA), are primarily known for their role in cell elongation, bud formation, and most importantly, root initiation and development.

In the natural setting, auxins are produced in the shoot tips and are transported down the stem, influencing the growth rates of various plant parts. They help maintain apical dominance — the phenomenon where the central stem of the plant grows more strongly than the side stems. Some auxins are also synthesized in developing seeds and fruits, contributing to fruit growth.

Knowing how and when to use synthetic auxin-like IBA is key in horticulture. It can be applied to promote rooting but must be carefully controlled as over-application can lead to abnormal growth or plant damage.

Stem Cutting Propagation

Stem cutting propagation is a asexual plant reproduction technique that involves taking a stem section from a parent plant and encouraging it to develop roots. This method is both simple and cost-effective, making it popular among horticulturists and hobbyists alike. The cutting, which includes a node and a small portion of stem, will develop roots either in soil, water, or a growing medium once properly treated with hormones like IBA.

The major advantages of this technique include the propagation of new plants that are genetically identical to the parent plant, and the preservation of desirable traits. It is also quicker than growing a plant from seed. For optimal results, the cuttings should be taken from healthy plants during their active growth phase, and the cut end should be kept moist until the roots form. With the aid of rooting hormone applications, this process can be significantly expedited and the chances of successful root formation greatly increased.