NCERT grounding
This subtopic sits in the Tissue Culture section that closes the chapter Strategies for Enhancement in Food Production. The old-NCERT supplement records that, during the 1950s, scientists learnt whole plants could be regenerated from explants — any part of a plant grown in a test tube under sterile conditions on a special nutrient medium. The capacity to generate a whole plant from any cell or explant is totipotency. Two applied techniques build on it: micropropagation, which multiplies plants in bulk, and somatic hybridisation, which fuses protoplasts to create hybrids.
"This method of producing thousands of plants through tissue culture is called micro-propagation. Each of these plants will be genetically identical to the original plant from which they were grown, i.e., they are somaclones."
That single sentence anchors three NEET-favourite terms — micropropagation, genetic identity, and somaclone. Every fact below is drawn from this NCERT supplement.
Micropropagation & somaclones
Micropropagation is the production of thousands of plants through tissue culture in a very short duration. An explant is placed on a nutrient medium, induced to form a mass of undifferentiated cells, and then coaxed by hormonal balance into shoots and roots that grow into complete plantlets. Because a single parent plant can supply many explants, and each explant yields many plantlets, the multiplication factor is enormous.
The defining property of micropropagation is that every plant it produces is genetically identical to the original plant — such a plant is called a somaclone. The plantlets arise by repeated mitotic division of cultured somatic cells, with no meiosis, no fertilisation and therefore no genetic recombination. Many important food plants — tomato, banana and apple — have been produced on a commercial scale by this method.
Plants per cycle
Micropropagation raises thousands of plants in a short duration from limited starting material — its single biggest advantage over seed-raised or cutting-raised stock.
The advantage is not only number but uniformity. Seed-raised crops segregate because sexual reproduction reshuffles alleles, so a field of seedlings is genetically variable. A field of somaclones is not — every individual carries the same desirable combination of traits as the elite parent.
Figure 1. An explant from the parent plant is cultured on nutrient medium, forms a dividing cell mass (callus), and regenerates into many plantlets. All offspring are somaclones — genetically identical to the parent.
Why "somaclone"
The prefix soma- signals that the clone arises from somatic (body) cells, not from gametes. For the exam, hold the NCERT line firmly: a somaclone is, by definition, genetically identical to the parent. Pair this with totipotency, the property that makes the whole regeneration possible in the first place.
Virus-free plants via meristem culture
A second, equally important application of tissue culture is the recovery of healthy plants from diseased plants. Viral infection cannot be cured by spraying, and an infected planting passes the virus on through every vegetative cutting. Tissue culture offers an escape route resting on one anatomical fact.
Even if the plant is infected with a virus, the meristem — apical and axillary — is free of the virus.
NCERT · Strategies for Enhancement in Food Production
The actively growing apical and axillary meristems divide faster than the virus can invade them, so they stay virus-free even in a heavily infected plant. If that meristem is excised and grown in vitro, the plantlet it regenerates carries no virus, and the whole crop can be re-established from this clean stock. Scientists have succeeded in culturing meristems of banana, sugarcane and potato to obtain virus-free plants.
Meristem culture — recovering a virus-free plant
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Step 1
Diseased plant
A virus-infected plant — its leaves and vascular tissue carry the pathogen.
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Step 2
Excise meristem
The apical or axillary meristem is removed; this tissue is free of the virus.
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Step 3
Culture in vitro
The meristem is grown on sterile nutrient medium and regenerates a plantlet.
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Step 4
Virus-free plant
A healthy plant is obtained — e.g. banana, sugarcane, potato.
Meristem culture is really micropropagation applied to a specific explant: the recovered plant is still a somaclone of the parent, but it lacks the virus the parent carried. This is why the NEET matching table pairs meristem culture with virus-free plants and micropropagation with somaclones.
Somatic hybridisation & protoplast fusion
Conventional hybridisation needs sexual compatibility, and distantly related species often will not cross at all. Somatic hybridisation sidesteps this barrier by fusing whole cells rather than uniting gametes. It is the production of a hybrid plant by fusing two protoplasts from two different plant varieties or species.
Isolating the protoplast
A protoplast is a naked plant cell — the living contents of a cell, bounded only by the plasma membrane, with the rigid cellulose wall removed. That wall is the obstacle: while it is present, two cells cannot merge. Scientists isolate protoplasts by digesting the wall away with enzymes — typically cellulase and pectinase. What remains is a free, membrane-bound protoplast, still fully alive and now able to fuse.
Three things define a protoplast for NEET: it is a plant cell, it has no cell wall, and it is still bounded by an intact plasma membrane.
Naked cell
A protoplast is a plant cell stripped of its cell wall, leaving only the plasma membrane.
Enzyme digestion
Cellulase and pectinase dissolve the wall, releasing the living protoplast intact.
Free to fuse
Wall-less protoplasts from two plants can merge into a single hybrid protoplast.
Two protoplasts — each from a different variety or species, each carrying a desirable character — are then induced to fuse. The fused product is a hybrid protoplast containing the genetic material of both parents. Grown on a suitable medium, it regenerates a cell wall and develops into a complete plant. That plant is a somatic hybrid, and the process is somatic hybridisation.
Figure 2. Enzymes digest the walls of potato and tomato cells to release naked protoplasts; the two protoplasts fuse into a hybrid protoplast that regenerates into the somatic hybrid — pomato.
Pomato — the classic somatic hybrid
The textbook example is pomato: a somatic hybrid produced by fusing a protoplast of potato with a protoplast of tomato. The hybrid plant was achieved — proof that protoplast fusion can cross species that no pollination could. But pomato did not possess all the desired combination of characteristics, so it could not become a commercially viable crop. For NEET, the pomato story carries two testable points: it demonstrates that somatic hybridisation works, and it shows that a successful fusion does not guarantee a useful plant.
Micropropagation
One parent
multiplied identically
- Goal: mass-produce plants — thousands per cycle
- Starts from an explant of a single plant
- Output is a somaclone — genetically identical to the parent
- No new gene combination is created
- Examples: tomato, banana, apple grown commercially
Somatic hybridisation
Two parents
protoplasts fused
- Goal: combine traits of two varieties/species
- Starts from protoplasts — naked, wall-less cells
- Output is a somatic hybrid — carries both genomes
- A new gene combination is created
- Example: pomato (potato × tomato)
Both techniques are in-vitro and both rest on totipotency, yet their logic is opposite. Micropropagation conserves a genotype and copies it; somatic hybridisation builds a new genotype that sexual reproduction could not assemble.
Worked examples
A horticulturist needs ten thousand virus-free banana plants from one infected elite mother plant. Which techniques achieve this, and what is the product called?
The mother plant is infected, but its meristem is virus-free. The horticulturist excises the apical or axillary meristem and grows it in vitro (meristem culture), then multiplies it by micropropagation to raise thousands of plantlets. Each plantlet is a somaclone — genetically identical to the parent — but free of the virus.
Why must the cell wall be removed before two plant cells can be fused in somatic hybridisation, and which agents remove it?
The rigid cellulose wall physically prevents two cells from merging — their plasma membranes cannot make contact through it. Removing the wall yields a protoplast, a naked cell bounded only by the plasma membrane, which can fuse with another protoplast. The wall is digested away enzymatically using cellulase (which breaks down cellulose) and pectinase (which dissolves the pectin cementing cells together).
Pomato was produced in the laboratory yet never became a commercial crop. State the technique used and the reason for its failure.
Pomato was produced by somatic hybridisation — the fusion of a potato protoplast with a tomato protoplast to give a somatic hybrid. The fusion and regeneration worked, but the hybrid did not have all the desired combination of characteristics, so it could not be commercially exploited.
Common confusion & NEET traps
The 2021 match-the-column item shows how this subtopic is examined: four terms each paired with the right partner. The traps below cover the swaps that lose marks.