Important Questions for CBSE Class 12 Biology Plant Breeding

Strategies for Enhancement in Food Production Important Questions for CBSE Class 12 Biology Plant Breeding

1.Plant breeding is a technique of manipulation of plant species, in order to create
desired plant types that are better suited for cultivation, give better yields and are
disease resistant.

2. The traits or characters that the breeders have tried to incorporate into crop plants are:
(i) Increased tolerance to environmental stresses, such as salinity, extreme temperatures, drought, etc.
(ii) Resistant to pathogens like viruses, fungi and bacteria.
(iii) Increased tolerance to insect pests.
(iv) High-yield and improved quality of crop plants.

3.Plant breeding programmes are carried out in government institutions and commercial companies.
The major steps in breeding a new genetic variety of crops are:
(i) Collection of Variability
(a) Genetic variability is the root of any breeding programme.
(b) Pre-existing genetic variability available from wild varieties, species and relatives of crop species is collected and preserved.
(c) Evaluation of their characteristics is a pre-requisite for the effective exploitation of natural genes available in the populations.
(d) The entire collection of plants/seeds having all the diverse alleles for all genes in a given crop is called germplasm collection.
(ii) Evaluation and Selection of Parents
(a) It is carried out by evaluating germplasm, to identify plants with desirable combination of characters.
(b)The selected plants are multiplied and hybridised.
(c) By self-pollination, purelines are created whenever desired.
(iii) Cross Hybridisation among Selected Parents
(a) Cross hybridisation is carried out to combine desired genetic characters from two ‘ different plants (parents).
(b) Cross hybridisation is a time consuming and tedious process, as it involves collection of pollen grains from the desired plants and other pollination techniques to incorporate desired traits.
(c) It is not certain that the hybrids would combine desired characters. The chances of
desirable combination is usually only one in few hundred to a thousand crosses carried out
(iv) Selection and Testing of Superior Recombinants
(a) This step consists of selection of plants among the progeny of the hybrids withdesired combination of characters.
(b) It yields plants that are superior than both the parents. This is known as
hybrid vigour/heterosis.
(c) They are self-pollinated for several generations, till they reach a state of uniformity or homozygosity, so that the characters will not segregate in the progeny.
(v) Testing, Release and Commercialisation of New Cultivars
(a) Evaluation is done for newly selected lines for their yield and other agronomic traits of quality, disease resistance, etc.
(b) Selected plants are grown in research fields and their performance is recorded under ideal fertiliser application, irrigation and other crop management practices.
(c) Testing of hybrid line is done in farmer’s field after evaluation. After testing, the crop is grown at different locations in the country with different agroclimatic zones for atleast three growing seasons.
(c) The tested material is evaluated in comparison to the best available local crop cultivar used as reference cultivar.
(d) Release of tested material is finally done in bulk after selection and certification.

4. Green Revolution
(i)It is the movement that led to the development of several high yielding varieties of wheat and rice in the mid 1960s.
(ii) Green revolution was dependent mainly on plant breeding techniques for the development of high-yielding and disease-resistant varieties in wheat, rice, maize, etc.
(iii) It led to dramatic increase in food production in our country.
(iv) In India, agriculture accounts for approximately 33% of India’s GDP and employs nearly 62% of population.
(v) Wheat and rice During 1960-2000, the production of wheat increased from 11 million tonnes to 75 million tonnes, while the production of rice increased from 35 million tonnes to 89.5 million tonnes.
(a)This increased production was due to the introduction of semi-dwarf varieties of wheat and rice.
(b) Nobel Laureate Norman E Borlaug, developed semi-dwarf varieties of wheat, at the International Centre for Wheat and Maize Improvement in Mexico.
(c) Semi-dwarf varieties of rice were developed from IR-8 at The International Rice Research Institute (IRRI, Philippines) and Taichung Native-1 (in Taiwan).
(d) High-yielding and disease-resistant wheat varieties were introduced in India in 1963, e.g. Sonalika and Kalyan Sona.
(e) The semi-dwarf varieties were introduced in India in 1966.
(f) Better-yielding semi-dwarf varieties, i.e. Jaya and Ratna were developed in India.
(vii) Sugarcane Saccharum barberi of North India and Saccharum officinarum of South India were crossed to get sugarcane varieties of high yield, thick stems, high sugar and ability to grow in areas of North India.
(viii) Millets
(a) Hybrid breeding have led to the development of several high yielding varieties resistant to water stress.
(b) The successfully developed high yielding hybrid varieties are of maize, jowar and bajra.

5.Plant breeding for disease resistance is required as a wide range of fungal, bacterial and viral pathogens which affect the yield of cultivated crop species, especially in tropical climates.
(i) Resistance of the host plant is the ability to prevent the pathogen from causing disease and is determined by the genetic constitution of host plant.
(ii) Development of resistance in crops enhances production and reduces the dependance on use of fungicides and bacteriocides.
(iii) The causative agents of diseases in plants are:
(a) Fungi disease caused are brown rust of wheat, red rot of sugarcane, late blight of potato, etc.
(b) Bacteria black rot of crucifers, blight of rice, citrus canker, etc.
(c) Virus tobacco mosaic, turnip mosaic, etc.
Methods of Breeding for Disease Resistance
(i) Conventional breeding is carried out in following steps:
(a) Selection and screening of germplasm for the disease resistance.
(b) Hybridisation of selected parent plant.
(c) Selection and evaluation of hybrids.
(d) Testing and release of new varieties into the market.
(e) Some important varieties developed by conventional method are:
(f) Disadvantages of this method are:

Limited number of disease resistance genes have been identified in crop varieties or wild relatives.

(ii) Mutation breeding is a phenomenon by which genetic variation is achieved through changes in base sequences within genes, which creates a new character or trait absent in parental generation.
(a) It can also be defined as the process of breeding by artificially inducing mutations using chemicals dr radiations.
(b) Mutation breeding is carried out in the following steps:

Inducing mutations in plants by various means.
Screening the plant for resistance.
Selecting the desirable plant for multiplication or for breeding.

(c) In mung bean, resistance to yellow mosaic virus and powdery mildew were introduced by mutations.
(d) Resistance to yellow mosaic virus in bhindi (Abelmoschus esculentus) was transferredfrom a wild species and resulted in a new variety of A. esculentus called Parbhani Kranti.

6. Plant Breeding for Developing Resistance to Insect Pests
(i) Insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics.
(ii) The important characters that lead to pest resistance are:
(a) Hairy leaves in plants, e.g. resistance to jassids in cotton and cereal leaf beetle in wheat.
(b) Solid stem in wheat exhibits non-preference by stem sawfly.
(c) In cotton, smooth leaf and the absence of nectar repel boll worms.
(d) In maize, high aspartic acid, low nitrogen and sugar content protect them from stem borers.
(iii) Breeding methods for insect pest-resistance involve the same steps as those for any other agronomic trait like yield or quality.
(iv) Some crop varieties bred by hybridisation and selection for insect pest resistance are
7. Plant breeding for improved food quality is required because of the following reasons:
(i)Lack of sufficient food having adequate nutritional requirement in the world.
(ii) Majority of people are unable to buy enough fruits, vegetables, legumes, fish and meat and thus, suffer from deficiencies or ‘hidden hunger’.
(iii) Essential micronutrients are absent from diet that increases risk for disease, reduce lifespan and reduce mental abilities.
(iv) Biofortification is the process of developing crops with higher levels of vitamins, minerals, proteins and healthier fats to improve public health.
(v) The objectives of breeding for improved nutritional quality are to improve:
(a) Protein content and quality (b) Oil content and quality
(c) Vitamin content (d) Micronutrients and mineral content
(vi) Crops developed with improved nutrient content are as follow:
(a) Atlas 66 having high protein content was used as a donor for developing improved wheat varieties.
(b) Maize hybrids with increased amount of amino acids lysine and tryptophan were developed in year 2000.
(c) Iron-fortified rice with increased iron content. ,
(d) Indian Agricultural Research Institute (LARI), New Delhi have released some fortified crop varieties rich in certain vitamins, minerals, etc.

Carrot, spinach and pumpkin – Vitamin-A.
Bitter gourd, bathua, mustard, tomato – Vitamin-C.
Spinach and bathua – Iron and calcium.
Broad bean, lablab, french and garden pea — Protein.

8. Single Cell Protein (SCP) is an alternative protein source for animal and human nutrition from certain microorganisms like
(i) Microbes like Spirulina are grown on an industrial scale to obtain good protein.\
(ii) Advantages of SCP are as follow:
(a) Microbes can be grown on materials like wastewater from potato processing plants (containing starch), straw, molasses, animal manure and sewage. Thus, they are easy to grow.
(b) SCPs provide nutrient rich food like proteins, minerals, fats, carbohydrates and vitamins.
(c) Reduce environmental pollution due to above mentioned resource utilisation.
(d) Yield is high due to high rate of biomass production and growth (250 g of microorganism like Methylophilus methylotrophus is expected to produce 25 tonnes of protein).

9. Tissue culture is a technique of regeneration of whole plant from any part of a plant by growing it on culture medium under aseptic conditions.
(i) The capacity of a plant cell (explant) to grow into a whole plant is called totipotency.
(ii) Explant is the part of plant taken for tissue culture.
(iii)The method of growing or producing thousands of plants through tissue culture is called micropopagation.
(iv) The nutrient medium must provide a carbon source such as sucrose and also inorganic salts, vitamins, amino acids and growth regulators like auxins, cytokinins, etc.
(v) The plants produced from tissue culture are genetically identical to the original plant from which they are grown, so they are called
Advantages of tissue culture are:
(a) More number of plants can be produced in a short time.
(b) Disease-free plants can be developed from diseased plants.
(c) Seedless plants can be multiplied.

10. Various tissue culture techniques are as follow:
A. Meristem culture can be done to recover healthy plants from diseased plants.
(i) Meristem (apical and axillary) is the only virus-free part of a virus-infected plant.
(ii) Virus-free plants can be obtained by removing the meristem and growing it in vitro.
(iii) Plants developed successfully from meristem culture are banana, sugarcane, potato, etc.

B.Somatic hybridisation is the process of fusion of protoplast of different varieties or species of plant on a suitable nutrient medium in vitro to develop a somatic hybrid.
(i) Procedure
(a) Single cells from selected plants are isolated.
(b) Cell walls are digested by the enzymes like pectinase and cellulase to expose the marked protoplasts.
(c) Naked protoplasts are isolated from the plasma membrane.
(d) Isolated protoplasts are fused to obtain hybrid protoplasts under sterile conditions in special nutrient medium.
(e) Hybrid protoplasts obtained are cultured in a suitable medium to form new plant.
(ii) Pomato is a somatic hybrid, produced by the fusion of tomato and potato protoplasts.

Previous Years Examination Questions

1 Mark Questions

1. Write an alternate source of protein for animal and human nutrition. [All India 2014]
Ans. Single cell protein derived from microbes acts
one of the alternate source of protein for animal and human nutrition.

2. What are ‘true breeding lines’ that are used to study inheritance pattern of traits in plants? [Delhi 2014]
Ans. ‘The breeding lines’ used to study inheritance pattern of traits in plants are actually the pure homozygous plants for a particular trait, obtained through classical plant breeding, self-hybridisation and selection.

3. Identify the two correct statements from the following
(i) Apiculture means apical meristem culture.
(ii) Spinach is iron enriched.
(iii) Green revolution has resulted in improved pulse yields.
(iv) Aphids cannot infest rapeseed mustard. [All India 2014C]
Ans. The two correct statements identified are:
(i) Spinach is iron-enriched.
(ii) Aphids cannot infest rapeseed mustard.

4. Name any two diseases the ‘Himgiri’ variety of wheat is resistant to. [All India 2013]
Ans. Stripe rust and leaf rust are the two diseases that are resistant to ‘Himgiri’ variety of wheat.

5. Name the following

The semi-dwarf variety of wheat, which is high-yielding and disease resistant?
Any one interspecific hybrid mammal. [Delhi 2012]

Ans. (i) Sonalika and Kalyan Sona are the semi-dwarf varieties of wheat that are high-yielding and disease resistant.
(ii) Mule is an interspecific hybrid mammal.

6. Write the names of the semi-dwarf and high-yielding rice varieties developed in India after 1966. [Delhi 2012]
Ans. Jaya and Ratna are two semi-dwarf and high yielding rice varieties developed in India after 1966.

7. Why is the South Indian sugarcane preferred by agriculturists? [Foreign 2012]
Ans. The South Indian sugarcane has thick stemswith high sugar content, that is why it is preferred by agriculturists.

8. State the importance of biofortification. [All India 2011]
Ans.Biofortification improves the nutritional quality of food materials by breeding crops with higher vitamins, minerals or proteins content and is the most practical means to improve public health.

9. Name the organism commercially used for the production of single cell protein. [Delhi 2009]
Ans. Spirulina is used for the production of SCP.

10. How are the two following varieties of sugarcane different from each other?
(i) Saccharum barberi
(ii) Saccharum ofiicinarum [Delhi 2009]
Ans. (i) Saccharum barberi grows in North India. It has poor sugar content and yield. (ii) Saccharum officinarum grows in South India. It has thicker stems, more sugar content and yield.

11. Which of the following is the semi-dwarf wheat that is high-yielding and disease resistant?
Pusa Shubra, Kalyan Sona, Ratna [Foreign 2009]
Ans.Kalyan Sona is a semi-dwarf wheat variety.

12. Which of the foUowing produces single cell proteins?Sonalika, Spirulina, Saccharomyces. [Foreign 2009]
Ans. Spirulina produces single cell protein.

13. What is the economic value of Spirulina? [All India 2008]
Ans. Spirulina is rich in protein, minerals, vitamins,
fats and carbohydrates. It is thus employed in the commercial production of single cell protein, so as to provide alternate source of nutrition.

14. What is the economic value of Saccharum officinarum’? [Foreign 2008]
Ans. Saccharum officinarum has thicker
stems and higher sugar content and yield. It is crossed with S. barberi to get varieties of high yield.

2 Marks Questions
15. How can healthy potato plants beobtained from a desired potato variety which is viral infected? Explain. [Delhi 2014]
^or
A potato plant is infected with a virus name and explain a method to obtain virus-free potato plants from it. [2014C]
Ans.The healthy potato plants can be obtained through meristem culture of viral infected plants. Since, meristematic tissues are free from virus and other infections. They are used as explants and cultured under in vitro conditions to produce new healthy potato plants, by micropropagation or tissue culture.

16. List two steps that are essential for carrying out artificial hybridisation in crop plants and why? [Foreign 2014]
Ans. The two steps are essential for carrying out artificial hybridisation in crop plants, as it is mandatory to prevent both self-pollination as well as unwanted cross-pollination. This is achieved by
(i) Emasculation Removal of anthers or stamens from bisexual flowers, in developing stage only.
(ii) Bagging The emasculated bisexual and unisexual flowers are covered with bag, i.e. butter paper so as to prevent any kind of unwanted pollination

17. How does culturing of Spirulina solve the food problems of the growing population? [Foreign 2012]
Ans. Culturing of Spirulina can solve the food problem of growing population by producing single cell protein. Because, it can be grown easily on wastewater animal manure and even sewage and obtained in large quantities. It can serve as source of food rich in minerals, vitamins, carbohydrates and proteins.

18. How is it possible to recover healthy banana plants from a diseased but desirable quality banana plant? Explain. [Foreign 2012]
Ans.Healthy plant is obtained from diseased plant by meristem culture.
In infected plant, meristems are free from viruses and it is excised and grown in test tubes or petriplate under sterile conditions, on suitable growth medium. By this method, a number of plant can be produced in a short duration and the process is called micropropogation.

19.How are biofortified maize and wheat considered nutritionally improved? [Foreign 2012]
Ans.Biofortified maize variety has twice the amount of amino acids, lysine and tryptophan, as compared to normal varieties. While biofortified wheat variety is very rich in protein content.

20. Explain the advantage of cross-breeding of two species of sugarcane in India. [Delhi 2011]
Ans. Sugarcane grown in North India, i.e. Saccharum barber/ has poor sugar content and low yield while, the sugarcane grown in South India, i.e. Saccharum officinarum has thicker stems and higher content of sugar, but cannot grown in North Indian climatic conditions.
The hybrid produced by cross breeding these two species has the following desirable traits :
(i) High-yield (ii) Thick stems (iii) High sugar content
(iv) Ability to grow in North Indian sugarcane fields.

21.Enumerate, in sequential order, the four steps that a plant breeder should follow to obtain a disease resistant Crop. [Delhi 2009C]
Ans. Steps to be followed by a plant breeder to get disease-resistant crops are:
(i) Screening germplasm for resistance.
(ii) Hybridisation of selected parents.
(iii) Selection and evaluation of the hybrids.
(iv) Testing and release of new varieties.

22. (i) What is micropropagation? Why are the plants produced by micropropagation called somaclones?
(ii) Name the techniques by which healthy plants can be recovered from diseased plants. [Foreign 2008]
Ans.(i) Micropropagation is a method of producing thousands of plants through tissue culture. Each plant will be genetically identical to the original plant from which they were grown. So, they are called somaclones.
(ii) Healthy plants can be recovered from diseased plants by meristem culture because meristems are free from viruses in diseased plant.

23. (i) Mention two ways of inducing artificial mutation in a crop field.
(ii) List two steps that help in introducing the desired mutation into the crop. [All India 2009C]
Ans. (i) Artificial mutation in a crop field can be induced by
(a) Use of chemicals.
(b) Use of radiations like gamma radiation.
(ii) After inducing mutations they can be introduced into crop, by these two steps:
(a) Selection of plants having desirable character as a source for breeding.
Hybridisation of the selected plants

24. List any four objective that you would recommend for biofortification.
[Delhi 2008C]
Ans. Objectives of biofortification are to increase
(i) Protein content and quality.
(ii) Oil content and quality.
(iii) Vitamin content.
(iv) Micronutrient and mineral content

25. How somaclones are produced? How are they different from somatic hybrids? [Delhi 2008C]
Ans. Somaclones are produced through micropropagation and tissue culture.
They are different from somatic hybrids in following ways:
3 Marks Questions
26. What is ‘biofortification’? Write its importance. Mention the contribution of Indian Agricultural Research Institute towards it with the help of two examples.[Foreign 2014]
Ans. (i) Biofortification improves the nutritional quality of food materials by breeding crops with higher vitamins, minerals or proteins content and is the most practical means to improve public health.
(ii) Importance of biofortification:

It provides the crops with higher levels of vitamins, minerals, proteins and healthier fats.
It helps in the improvement of public health.

(iii) Contribution of IARI towards biofortification is by developing several vegetable crops rich in vitamins and minerals.
Two examples of such crops are :
(a) Vitamin-A enriched carrots and spinach.
(b) Protein enriched beans.

27. Suggest and describe a technique through which a virus-free healthy plant can be obtained from a diseased sugarcane plant. [2014 c]
Ans. The virus-free healthy sugarcane plant can
be obtained through meristem culture of diseased plant; as meristematic tissues are free from viruses they can be used as explants for micropropagation.
Steps in Meristem Culture
(i) The shoot tip explants are grown in nutrient medium in either a test tube a pteri dish, under aseptic/sterile in vitro conditions.
(ii) The nutrient medium should essentially have a carbon source inorganic salts vitamins, amino acids and growth regulators like auxin and cytokinin in proper defined ratio.
(iii) The plantlets, thus obtained are later shifted to nurseries, under observation and finally to fields.

28. Name the prominent South Indian and North Indian species of sugarcane used for cross breeding. List the desired qualities of the hybrid that can be obtained from this cross.[Delhi 2013C]
Ans. North Indian species of sugarcane is Saccharum barberi. South Indian species of Sugarcane is Saccharum officinarum.(l) The hybrid obtained from this cross is supposed.
Sugarcane grown in North India, i.e. Saccharum barber/ has poor sugar content and low yield while, the sugarcane grown in South India, i.e. Saccharum officinarum has thicker stems and higher content of sugar, but cannot grown in North Indian climatic conditions.
The hybrid produced by cross breeding these two species has the following desirable traits :
(i) High-yield (ii) Thick stems (iii) High sugar content
(iv) Ability to grow in North Indian sugarcane fields.

29. (i) Name the Indian scientist, whose efforts brought ‘Green Revolution in India’.
(ii) Mention the steps that are essentially carried out in developing a new genetic variety of crop under plant breeding programme. [Foreign 2012]
Ans. (i) MS Swaminathan brought ‘Green Revolution’ in India.
(ii) The steps in developing a new genetic variety of crops are:

Collection of genetic variability or germplasm.
Evaluation and selection of parents.
Cross hybridisation among the selected parents.
Selection and testing of superior recombinant or hybrids.
Testing, release and commercialisation of new cultivars.

30. How can crop varieties be made disease resistant to overcome food crisis in India?
Name one disease resistant variety in India of

Wheat to leaf and stripe rust.
Brassicato white rust. [Delhi 2011]

Ans. To overcome food crisis due to crop failure or disease, ways to make disease resistant crop varieties have developed
(i) By conventional breeding techniques It includes

Screening the germplasm for the source of resistance.
Hybridisation of selected individuals.
Selection and evaluation of hybrids.
Evaluation of hybrids.
Testing and release of the variety.

(ii) By mutation breeding It involves inducing mutations artificially and then using the plants that have the desirable character as a source of disease-resistance in breeding.

Himgiri wheat is resistant to leaf and stripe rust.
Pusa Swarnim (Karan Rai) is resistant to white rust.

31. Mention the property of plant cells that has helped them to grow into a new plant in in vitro Explain the advantages of micropropagation. [Delhi 2011]
Ans. Plant cell has a property called ‘totipotency’ by which each cell can grow into a new plant under in vitro conditions.
Advantages of micropropagation are:

(i) Thousands of plants can be grown in a short period.
(ii) By culturing the meristems of virus infected plants, virus-free healthy plants can be raised.
(iii) Plants are genetically identical, so certain desirable characters can be continued through generations.
(iv) Hybrids can be produced by somatic hybridisation.

32. Scientists have succeeded in recovering healthy sugarcane plants from a diseased one

Name the part of the plant used as explant by scientists.
Describe the procedure the scientists followed to recover the healthy parts.
Name the technology used for crop improvement. [All India 2011]

Ans. (i) Shoot tip or meristems of plant.
(ii) The virus-free healthy sugarcane plant can be obtained through meristem culture of diseased plant; as meristematic tissues are free from viruses they can be used as explants for micropropagation.
Steps in Meristem Culture
(i) The shoot tip explants are grown in nutrient medium in either a test tube a pteri dish, under aseptic/sterile in vitro conditions.
(ii) The nutrient medium should essentially have a carbon source inorganic salts vitamins, amino acids and growth regulators like auxin and cytokinin in proper defined ratio.
(iii) The plantlets, thus obtained are later shifted to nurseries, under observation and finally to fields.
(iv) Micropropagation is the technology used for crop improvement

33. IARI has released several varieties of crop plants that are biofortified. List three examples of such crops and their biofortifications. [Foreign 2011]
Ans. Biofortified crops released by IARI are:
(i) Vitamin-A enriched carrots and spinach.
(ii) Iron and calcium enriched spinach.
(iii)Protein enriched beans.
(iv) Vitamin-C enriched bitter gourd and mustard.

34. (i) Mention the property that enables the explants to regenerate into a new plant.
(ii) A banana herb is virus-infected. Describe the method that will help in obtaining healthy banana plants from this diseased plant. [All India 2010]
Ans. Totipotency of cells is the property that enables the explants to regenerate into a new identical plant.
(ii) Meristem culture is the method by which healthy banana plants can be obtained from virus-infected plant. The apical and axillary meristem is free of virus. The meristem is removed from the plant and grown in vitro by micropropagation. The plants thus, produced are virus-free.

35. How are somaclones cultured from explants in in vitro conditions? Why are somaclones so called?
[Foreign 2010]
^or
Why are plants obtained through micropropagation termed somaclones? Name three food plants produced on commercial scale using this method. [All India 2009C]
Ans. Somaclones cultured from explants are grown in following steps:
(i) The explant is grown in a petri dish/test tube under sterile conditions in a special nutrient medium.
(ii) The medium must contain carbon source like sugar, inorganic salts, vitamins, minerals, amino acids, growth regulators like auxins and cytokinins.
(iii) The medium should be replaced regularly to restore nutrients in it.
(iv) Because all plants (produced by tissue culture) are genetically identical to the original plant (from where they are cultured), so they are called somaclones. Three food plants produced by micropropagation are tomato, banana, apple, etc.

36. Define totipotency of a cell. List the requirements, if the objective is to produce somaclones of a tomato plant on commercial scale.[Foreign 2008]
Ans. Totipotency of a cell can be defined as the capacity of a cell/explant to grow into a whole new identical plant.
Requirements to produce somaclones of tomato plants are:
(i) Explant It is any part of a plant taken out for growing a new plant in special nutrient medium under sterile/aseptic conditions.
(ii) Nutrient medium It must have a carbon source such as sugar, inorganic salts, vitamins, amino acids, growth regulators like auxins, cytokinins, etc.
(iii) Suitable conditions of light and temperature. This is a tissue culture method by which a number of genetically similar plants called somaclones can be grown.
(iv) The plant let grown are later shifted to nurseries for further development and finally to fields.

37. (i) What is micropropagation? Why are the plants produced by micropropagation called somaclones?
(ii) Name the technique by which healthy plants can be recovered from the diseased plants. [Foreign 2008]
5 Marks Questions

38. With advancements in genetics, molecular biology and tissue culture, new traits have been incorporated into crop plants.
Explain the main steps in breeding a new genetic variety of a crop.
[All India 2014]
Ans. The major steps in breeding a new genetic variety of a crop are:
(a) Collection of variability Genetic variability is the root of any breeding programmes. Wild varieties of many related crops are collected for evaluation.
(b) Evaluation and selection of parents Germplasm of the identified plants are evaluated for desired characters.
(c) Cross hybridisation The desired characters are obtained by crossing the wild selected species of crops.
(d) Selection and testing of superior recombinants The superior plants after cross hybridisation are selected and tested in all respects before making it for commercialisation.
(e) Commercialisation of new variety

39. (i) Name the technology that has helped scientists to propagate on a large scale the desired crops in a short duration. List the steps carried out to propagate the crops by the said technique.
(ii) How are somatic hybrids obtained? [Delhi 2014]
Ans. (i) Tissue culture is the technique that has helped scientists to propagate plants with desirable traits on a large scale, in short duration. Since, large number of plants are propagated through this culture it is also referred to as micropropagation.
The steps involved in this technique are:

Explants are derived from any part of plant (to be propagated), i.e. tips of carrot.
Explants are grown in sterile conditions in special nutrient media to regenerate complete plants.
Nutrient media must contain a carbon source (such as sucrose), organic salts, vitamins, amino acids and phytohormones, i.e. auxin and cytokinin.
Hence, propagation is achieved for a large number of plants under in vitro
All the plants obtained by tissue culture are called somaclones, since they are genetically identical to each other as well as, to the parent plant.

(ii) Somatic hybrids are obtained by the method of somatic hybridisation. In this method, the naked protoplasts of cells of two plants are hybridised. Protoplasts are isolated by dissolving cell wall and fused to get a hybrid protoplast. The fused nucleus is called heterokaryon that , grows further to form a new plant. The plants thus formed are called somatic hybrid

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