Q.Name the technique and the property of plant cells that can help to grow somaclones of certain desired variety of apple. Explain how somaclones of apple can be obtained in the lab so as to get the desired variety on a large scale.

Concept: Somaclonal variation — the genetic variation seen in plants regenerated from tissue culture — exploited for clonal propagation.

Key property: Plant cells are totipotent; any somatic cell can dedifferentiate, form a callus, and regenerate a whole plant genetically identical to the parent (a somaclone).

Steps to obtain apple somaclones on a large scale:

1. Explant selection: Take a small piece of somatic tissue (e.g., leaf or stem segment) from a desired apple variety.
2. Callus induction: Culture the explant on a sterile nutrient medium with auxins and cytokinins to produce an undifferentiated callus. …

Concept and Intuition

Apple trees are heterozygous and seed propagation gives highly variable offspring — not true to the parent. To get a large number of genetically identical plants of a desired variety (e.g., a disease-resistant or high-yielding apple), we bypass sexual reproduction entirely. The trick lies in totipotency: every living plant cell contains the full genetic blueprint to form a complete plant. By isolating somatic (non-reproductive) cells from a superior apple tree and growing them under controlled conditions, we can produce hundreds of clones — called somaclones — each identical to the parent.

The technique used is tissue culture — more precisely, micropropagation via somatic embryogenesis or organogenesis. This should not be confused with somatic hybridisation, a different technique (fusion of protoplasts from two different species) that is not what is used here; the method for producing apple somaclones is simply culturing somatic cells of the same variety.

Step-by-Step Explanation

1. Select the donor plant

   Choose a healthy, desired apple variety (e.g., a specific cultivar with good fruit quality or disease resistance). Take a small piece of living tissue — typically a young leaf, stem segment, or shoot tip. This is the explant.

2. Surface sterilise the explant

   Wash the explant with a mild detergent, then treat with a sterilising agent like 0.1% mercuric chloride or 70% ethanol for a few minutes, followed by several rinses with sterile distilled water. This kills surface microbes without damaging the plant cells.

3. Culture on nutrient medium

   Place the sterile explant on a semi-solid Murashige and Skoog (MS) medium supplemented with specific plant growth regulators. For callus induction, use a high auxin-to-cytokinin ratio (e.g., 2,4-D at 2–5 mg/L). The cells dedifferentiate and form an undifferentiated mass called callus.

4. Induce regeneration

   Transfer the callus to a medium with a different hormone balance — typically higher cytokinin (e.g., BAP at 1–3 mg/L) and lower auxin. This triggers organogenesis (shoot formation) or somatic embryogenesis (embryo-like structures). Each shoot or embryo arises from a single somatic cell, so all are genetically identical to the parent.

5. Rooting and hardening …