Production of Virus-Free Plants
(Different Methods – Brief Account)
Introduction
Plant viruses cause serious yield losses and quality deterioration in crops, especially in vegetatively propagated plants like potato, sugarcane, banana, cassava, citrus, and ornamentals. Since chemical control of viruses is ineffective, production of virus-free plants using tissue culture–based techniques is the most reliable approach.
1. Meristem Culture (Shoot Tip Culture)
Principle
Viruses are generally absent or present in very low concentration in the apical meristem (0.1–0.5 mm) because of rapid cell division and lack of vascular connections.
Method
Excise apical or axillary meristem under sterile conditions
Culture on nutrient medium (e.g., MS medium with cytokinins)
Regenerate whole plants
Index regenerated plants for virus presence
Advantages
Highly effective
Maintains genetic uniformity
Widely used commercially
Limitations
Technically demanding
Survival rate of tiny meristems is low
2. Thermotherapy
Principle
Many plant viruses are heat-sensitive, while host tissues can tolerate higher temperatures for short durations.
Method
Infected plants or in vitro cultures exposed to 35–40°C for several weeks
Heat treatment reduces virus multiplication
Meristems are excised and cultured after heat treatment.
Advantages
Simple method
Increases success of meristem culture
Limitations
Heat stress may damage plant tissues
Not effective for all viruses
3. Chemotherapy
Principle
Use of antiviral chemicals inhibits viral replication in plant tissues.
Common Chemicals
Ribavirin
Acyclovir
Virazole
Method
Antiviral compounds added to culture medium
Treated explants regenerated into plants
Advantages
Useful for stubborn viruses
Can be combined with meristem culture
Limitations
Phytotoxic effects
High cost
Incomplete virus elimination
4. Cryotherapy
Principle
Virus-infected cells are killed during ultra-low temperature treatment, while meristematic cells survive.
Method
Shoot tips treated with cryoprotectants
Rapid freezing in liquid nitrogen (−196°C)
Thawing and regeneration of plants
Advantages
Highly efficient virus elimination
Suitable for long-term germplasm conservation
Limitations
Requires specialized equipment
Technical expertise needed
5. Micrografting
Principle
Healthy meristem is grafted onto a virus-free rootstock, allowing development of virus-free shoots.
Method
Excise small meristem
Graft onto sterile seedling rootstock in vitro
Grow under controlled conditions
Advantages
Useful for woody plants (e.g., citrus, apple)
Maintains varietal traits
Limitations
Technically complex
Time-consuming
6. Electrotherapy
Principle
Electric current damages viral nucleic acids without killing plant cells.
Method
Plant tissues exposed to controlled electric current
Followed by meristem culture
Advantages
Simple and fast
Effective for some viruses
Limitations
Not widely standardized
Limited application
7. Combination Treatments
Examples
Thermotherapy + Meristem culture
Chemotherapy + Meristem culture
Cryotherapy + Meristem culture
Importance
Combination treatments increase virus elimination efficiency, especially for persistent viruses.
Virus Indexing and Confirmation
After regeneration, plants must be tested using:
ELISA
PCR / RT-PCR
Indicator plants
Electron microscopy
Conclusion
Production of virus-free plants is essential for sustainable agriculture and quality planting material. Meristem culture, often combined with thermotherapy, chemotherapy, or cryotherapy, is the most effective and widely used approach. These techniques ensure healthy, high-yielding, and genetically uniform plants.
Production of Virus-Free Plants
50 MCQs with Answers
Virus-free plants are mainly produced using
A. Seed treatment
B. Tissue culture techniques
C. Fertilizer application
D. Crop rotation
Answer: B
The most commonly used method for producing virus-free plants is
A. Callus culture
B. Meristem culture
C. Protoplast culture
D. Anther culture
Answer: B
Viruses are absent in meristems mainly because of
A. Lack of nutrients
B. Rapid cell division
C. High temperature
D. Thick cell wall
Answer: B
The size of meristem used for virus elimination is usually
A. 5–10 mm
B. 2–3 mm
C. 0.1–0.5 mm
D. 1–2 cm
Answer: C
Meristem culture is especially useful for
A. Seed-propagated crops
B. Vegetatively propagated crops
C. Forest trees only
D. Algae
Answer: B
Potato virus-free plants are commonly produced by
A. Anther culture
B. Meristem culture
C. Embryo culture
D. Cell suspension
Answer: B
Thermotherapy is based on the principle that viruses are
A. Heat tolerant
B. Cold tolerant
C. Heat sensitive
D. Light sensitive
Answer: C
The temperature range used in thermotherapy is approximately
A. 20–25°C
B. 25–30°C
C. 35–40°C
D. 45–50°C
Answer: C
Thermotherapy is usually followed by
A. Callus culture
B. Meristem culture
C. Seed germination
D. Grafting
Answer: B
One disadvantage of thermotherapy is
A. Genetic variation
B. Tissue damage due to heat
C. Poor rooting
D. Increased virus multiplication
Answer: B
Chemotherapy involves the use of
A. Antibiotics
B. Antiviral chemicals
C. Insecticides
D. Fungicides
Answer: B
A commonly used antiviral chemical in plant tissue culture is
A. Streptomycin
B. Ribavirin
C. Carbendazim
D. Penicillin
Answer: B
Chemotherapy works mainly by
A. Killing plant cells
B. Inhibiting viral replication
C. Enhancing photosynthesis
D. Increasing cell size
Answer: B
A major limitation of chemotherapy is
A. Virus resistance
B. Phytotoxicity
C. Genetic stability
D. High survival rate
Answer: B
Cryotherapy uses the temperature of
A. 0°C
B. −20°C
C. −80°C
D. −196°C
Answer: D
Cryotherapy is carried out using
A. Dry ice
B. Liquid nitrogen
C. Hot air
D. Steam
Answer: B
Cryotherapy eliminates viruses because
A. Viruses multiply rapidly
B. Infected cells are killed
C. Meristem cells die
D. Hormones are destroyed
Answer: B
Cryotherapy is also useful for
A. Mutation breeding
B. Germplasm conservation
C. Hybridization
D. Pollination
Answer: B
Micrografting is mainly used in
A. Herbaceous plants
B. Algae
C. Woody plants
D. Bryophytes
Answer: C
Citrus virus-free plants are often produced by
A. Meristem culture alone
B. Micrografting
C. Protoplast fusion
D. Anther culture
Answer: B
In micrografting, the scion used is a
A. Callus piece
B. Leaf disc
C. Meristem tip
D. Root segment
Answer: C
Electrotherapy uses
A. Chemicals
B. Heat
C. Electric current
D. Radiation
Answer: C
Electrotherapy eliminates viruses by damaging
A. Plant cell wall
B. Viral nucleic acids
C. Plant chromosomes
D. Chloroplast DNA
Answer: B
A combination of methods is preferred because it
A. Reduces cost
B. Increases efficiency
C. Reduces plant growth
D. Causes variation
Answer: B
The most effective combination for virus elimination is
A. Chemotherapy + grafting
B. Thermotherapy + meristem culture
C. Electrotherapy + fertilization
D. Cryotherapy + callus culture
Answer: B
Virus indexing means
A. Virus multiplication
B. Virus detection
C. Virus elimination
D. Virus storage
Answer: B
ELISA is used for
A. Virus detection
B. Virus destruction
C. Meristem excision
D. Grafting
Answer: A
PCR detects viruses at the level of
A. Protein
B. DNA/RNA
C. Cell wall
D. Enzymes
Answer: B
Indicator plants are used to
A. Grow viruses
B. Detect virus symptoms
C. Kill viruses
D. Store viruses
Answer: B
Electron microscopy detects viruses based on
A. Enzyme reaction
B. Light absorption
C. Particle structure
D. DNA amplification
Answer: C
Virus-free plants are important because they
A. Grow slowly
B. Increase yield
C. Reduce nutrition
D. Increase mutation
Answer: B
Chemical control of plant viruses is generally
A. Effective
B. Ineffective
C. Cheap
D. Permanent
Answer: B
Vegetatively propagated crops are prone to virus infection because
A. No seeds are formed
B. Viruses accumulate over generations
C. They grow slowly
D. They lack immunity
Answer: B
Sugarcane virus-free plants are commonly produced using
A. Seed culture
B. Meristem culture
C. Protoplast fusion
D. Anther culture
Answer: B
Banana virus-free plants are produced mainly by
A. Callus culture
B. Meristem culture
C. Leaf culture
D. Root culture
Answer: B
Which method maintains genetic uniformity best?
A. Mutation breeding
B. Meristem culture
C. Callus culture
D. Protoplast culture
Answer: B
Cryoprotectants are used in cryotherapy to
A. Kill viruses
B. Protect tissues from freezing injury
C. Increase hormones
D. Promote callus
Answer: B
The success of meristem culture depends mainly on
A. Meristem size
B. Light intensity
C. Soil fertility
D. Humidity
Answer: A
Virus-free plants are also called
A. Mutant plants
B. Index-tested plants
C. Hybrid plants
D. Transgenic plants
Answer: B
Which virus elimination method is most technically demanding?
A. Thermotherapy
B. Chemotherapy
C. Cryotherapy
D. Seed treatment
Answer: C
Chemotherapy is often combined with
A. Fertilization
B. Meristem culture
C. Grafting
D. Pollination
Answer: B
Meristem culture avoids virus spread because of absence of
A. Cell wall
B. Vascular tissue
C. Nucleus
D. Cytoplasm
Answer: B
Virus-free planting material ensures
A. Uniform disease spread
B. Healthy crop establishment
C. Reduced growth
D. Genetic variation
Answer: B
Which crop benefits most from virus-free technology?
A. Wheat
B. Rice
C. Potato
D. Maize
Answer: C
Virus elimination is least effective in
A. Meristem culture
B. Combination methods
C. Direct field selection
D. Cryotherapy
Answer: C
Antiviral chemicals act mainly during
A. Cell division
B. Viral replication
C. Protein synthesis
D. Photosynthesis
Answer: B
Virus-free plants are essential in
A. Organic farming
B. Seed banks
C. Horticulture and agriculture
D. Forestry only
Answer: C
In vitro methods are preferred because they are
A. Slow
B. Unreliable
C. Precise and controlled
D. Seasonal
Answer: C
Virus-free plants help in
A. Increasing mutation rate
B. Reducing crop yield
C. Improving planting material quality
D. Spreading disease
Answer: C
The ultimate goal of virus-free plant production is
A. Genetic modification
B. Disease-free, high-yield crops
C. Hybrid seed production
D. Mutation induction
Answer: B
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