Plant Breeding

Class 12 | Biology — Botany | Chapter 9

Class 12 Unit 9 Biology

Learning Objectives

The learner will be able to:

• Appreciate the relationship between humans and plants.
• Recognise the origin of agriculture.
• Perceive the importance of organic agriculture.
• Understand the different conventional methods of plant breeding.

Chapter Outline

• 9.1 Relationship between human and plants
• 9.2 Domestication of plants
• 9.3 Origin of agriculture
• 9.4 Organic agriculture
• 9.5 Plant breeding
• 9.6 Conventional plant breeding methods
• 9.7 Modern plant breeding Techniques

Economic botany is the study of the relationship between people and economically important plants. It explores the ways by which humans use plants for food, medicines and other uses. Economic botany intersects many fields including established disciplines such as agronomy, anthropology, archaeology, chemistry, trade and commerce.

9.1 Relationship between Humans and Plants

From the very early times, human beings have co-existed with plants which played a vital role in their survival. Through a long process of trial and error, our ancestors have selected hundreds of wild plants from the various parts of the world for their specific use. The knowledge of the plants and its applications have led to the development of the humans and their civilization in many ways.

9.2 Domestication of Plants

Domestication is the process of bringing a plant species under the control of humans and gradually changing it through careful selection, genetic alteration and handling so that it is more useful to people. The domesticated species are renewable sources that have provided food and other benefits to human.

Possible Changes in Plant Species due to Domestication

• Adaptation to a greater diversity of environments and a wider geographical range.
• Simultaneous/uniform flowering and fruiting.
• Lack of shattering or scattering of seeds.
• Increased size of fruits and seeds.
• Change from a perennial to annual habit.
• Change in breeding system.
• Increased yield.
• Increased resistance for disease and pest.
• Developing seedless parthenocarpic fruit.
• Enhancing colour, appearance, palatability and nutritional composition.

9.3 Origin of Agriculture

Archeological evidence for earliest record of agriculture is found in the fertile crescent region in and around Tigris and Euphrates river valleys, approximately about 12,000 years ago. The earlier Greek and Roman naturalists like Theophrastus, Dioscorides, Pliny the elder and Galen laid down the scientific foundation in understanding origin and domestication of cultivated plants.

9.4 Organic Agriculture

Organic farming is an alternative agricultural system which originated early in the twentieth century in reaction to rapidly changing farming practices. It is a production system that sustains the health of the soils, ecosystems and people. It relies on ecological processes, biodiversity and cycles adapted to local conditions rather than the use of inputs with adverse effects.

9.4.1 Biofertilizers

What are Biofertilizers?

Biofertilizers are defined as preparations containing living cells or latent cells of efficient strains of micro organisms that help crop plants uptake of nutrients by their interactions in the rhizosphere when applied through seed or soil. Biofertilizers could be also called as microbial cultures, bioinoculants, bacterial inoculants or bacterial fertilizers.

• They are efficient in fixing nitrogen, solubilising phosphate and decomposing cellulose.
• They are designed to improve the soil fertility, plant growth, and also the number and biological activity of beneficial microorganisms in the soil.
• They are eco-friendly organic agro inputs and are more efficient and cost effective than chemical fertilizers.

Do You Know?

Indian Plant Breeders

• a. Dr. M. S. Swaminathan – He is a pioneer mutation breeder.
• b. Sir. T.S. Venkataraman – An eminent sugarcane breeder.
• c. Dr. B.P. Pal – Famous wheat breeder, developed superior disease resistant varieties of wheat.
• d. Dr. K. Ramiah – Eminent rice breeder, developed several high yielding varieties of rice.
• e. N.G.P. Rao – An eminent sorghum breeder, developed world's first hybrid of Sorghum (CSH-1).
• f. C.T. Patel – Who developed world's first cotton hybrid.
• g. Choudhary Ram Dhan – Wheat breeder, who is famous for C-591 variety of wheat, which made Punjab the wheat granary of India.

Figure 9.1: Classification of Biofertilizers

[Figure 9.1: Classification of Biofertilizers]

Rhizobium

Bio-fertilisers containing rhizobium bacteria are called rhizobium bio-fertilizer culture. Symbiotic bacteria that reside inside the root nodules convert the atmospheric nitrogen into a bio available form to the plants. This nitrogen fixing bacterium when applied to the soil undergoes multiplication and fixes the atmospheric nitrogen in the soil. Rhizobium is best suited for the paddy fields which increase the yield by 15 – 40 percentage.

Figure 9.2 (a): Root nodules occur on root (b) C.S. of Root nodule

Azolla

Azolla is a free-floating water fern that fixes the atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaena azolla. It is used as a bio-fertilizer for wetland rice cultivation and is known to contribute 40 to 60 kg per ha per crop. The agronomic potential of Azolla is quite significant particularly for increasing the yield of rice crop, as it quickly decompose in soil.

Figure 9.3: (a) Azolla in paddy field (b) Azolla

Arbuscular Mycorrhizae

Arbuscular mycorrhizae (AM) is formed by the symbiotic association between certain phycomycetous fungi and angiosperm roots. They have the ability to dissolve the phosphates found in abundance in the soil.

Figure 9.4: Benefits of AM Colonisation

Apart from increasing the availability of phosphorus, AM provides necessary strength to resist disease, germs and unfavourable weather conditions. It also assures water availability.

Seaweed Liquid Fertilizer

Seaweed liquid fertilizer (SLF) contains cytokinin, gibberellins and auxin apart from macro and micro nutrients. Most seaweed based fertilizers are made from kelp (brown algae) which grows to length of 150 metres. Seaweed Liquid fertilizer is not only organic but also ecofriendly. The alginates in the seaweed that react with metals in the soil and form long, cross-linked polymers in the soil. These polymers improve the crumbing in the soil and are useful in organic gardening which provides carbohydrates for plants.

• Seaweed has more than 70 minerals, vitamins and enzymes.
• It promotes vigorous growth.
• Improves resistance of plants to frost and disease.
• Seeds soaked in seaweed extract germinate much rapidly and develop a better root system.

Figure 9.5: Seaweed – Kelp

Bio-Pesticides

Bio-pesticides are biological agents used for the control of plant pests. They are in high use due to their non-toxic, cheaper and eco-friendly characteristics as compared to chemical or synthetic pesticides. Bio-pesticides have become an integral component of pest management in terms of the environmental and health issues attributed to the use of chemicals in agriculture.

Trichoderma Species

Trichoderma species are free-living fungi that are common in soil and root ecosystem. They have been recognized as bio-control agent for:

1. The control of plant disease
2. Ability to enhance root growth development
3. Crop productivity
4. Resistance to abiotic stress
5. Uptake and use of nutrients

Figure 9.6 (b): Biopesticide (a) Trichoderma fungi

Beauveria species is an entomo-pathogenic fungus that grows naturally in soils throughout the world. It acts as a parasite on various arthropod species causing white muscardine disease without affecting the plant health and growth. It also controls damping off of tomato caused by Rhizoctonia solani.

Green Manuring

Green manuring is defined as the growing of green manure crops and use of these crops directly in the field by ploughing. One of the main objectives of the green manuring is to increase the content of nitrogen in the soil. Also it helps in improving the structure and physical properties of the soil.

Important Green Manure Crops

The most important green manure crops are Crotalaria juncea, Tephrosia purpurea, Indigofera tinctoria.

The green manuring can be practised as:

• Green in-situ manuring: Refers to the growing of green manuring crops in the border rows or as intercrops along with the main crops. Example: Sun hemp, Cowpea, Green gram etc.
• Green leaf manuring: The application of green leaves and twigs of trees, shrubs, plants growing in wastelands and field bunds. The important plant species useful for green leaf manure are Cassia fistula, Sesbania grandiflora, Azadirachta indica, Delonix regia, Pongamia pinnata etc.

Figure 9.7: (a) Beauveria Fungi (b) Beauveria sps infected insect on green plant (c) Entomopathogenic fungi on insects

9.5 Plant Breeding

Plant breeding is the science of improvement of crop varieties with higher yield, better quality, resistance to diseases and shorter durations which are suitable to particular environment. In other words, it is a purposeful manipulation of plant species in order to create desired genotype and phenotype for the benefit of humans. In early days, plant breeding activities were based mainly on skills and ability of person involved. But as the principles of genetics and cytogenetics have elucidated breeding methods such as selection, introduction, hybridization, ploidy, mutation, tissue culture and biotechnology techniques were designed to develop improved crop varieties.

9.5.1 Objectives of Plant Breeding

• To increase yield, vigour and fertility of the crop.
• To increase tolerance to environmental condition, salinity, temperature and drought.
• To prevent the premature falling of buds, fruits etc.
• To improve synchronous maturity.
• To develop resistance to pathogens and pests.
• To develop photosensitive and thermos-sensitive varieties.

9.5.2 Steps in Plant Breeding

Main Steps in Plant Breeding

• Creation of Genetic variation
• Selection
• Evaluation and release as a variety
• Seed multiplication and distribution
• Domestication / Plant introduction
• Hybridization
• Germplasm Collection
• Mutation
• Polyploidy
• Tissue culture
• Genetic engineering

Figure 9.8: Steps in Plant Breeding

9.6 Conventional Plant Breeding Methods

Conventional plant breeding methods resulting in hybrid varieties had a tremendous impact on agricultural productivity over the last decades. It develops new plant varieties by the process of selection and seeks to achieve expression of genetic material which is already present within the species.

9.6.1 Plant Introduction

Plant introduction may be defined as the introduction of genotypes from a place where it is normally grown to a new place or environment. Rice variety of IR8 introduced from Philippines and Wheat varieties of Sonora 63, Sonora 64 from Mexico. The newly introduced plant has to adapt itself to the new environment. This adjustment or adaptation of the introduced plant in the changed environment is called acclimatization. All the introductions must be free from presence of weeds, insects and disease causing organisms. This has to be carefully examined by the process called quarantine, a strict isolation imposed to prevent the spread of disease.

Types of Introduction

(1) Primary introduction – When the introduced variety is well adapted to the new environment without any alternation to the original genotype.

(2) Secondary introduction – When the introduced variety is subjected to selection to isolate a superior variety and hybridized with a local variety to transfer one or a few characters to them.

The botanical gardens in different parts of the world also played a significant role in plant introduction.

Example: Tea varieties collected from China and North East India initially grown in Botanical Garden of Kolkata from which appropriate clones have selected and introduced to different parts of India.

Do You Know?

National Bureau of Plant Genetic Resources (NBPGR)

The Bureau is responsible for introduction and maintenance of germ plasm of various agricultural and horticultural station in our country. It is also responsible for maintenance of plant materials of botanical and medicinal interest. It is located at Rangpuri, New Delhi and has four regional plant quarantine stations at Amritsar, Kolkata, Mumbai and Chennai at Meenambakkam.

9.6.2 Selection

Selection is the choice of certain individuals from a mixed population for one or more desirable traits. Selection is the oldest and basic method of plant breeding. There are two main types of Selection.

1. Natural Selection

This is a rule in nature and results in evolution reflected in the Darwinian principle "survival of the fittest". It takes longer time in bringing about desired variation.

2. Artificial Selection

It is a human involved process in having better crop from a mixed population where the individuals differ in character. The following are the three main types of artificial selection:

a. Mass Selection: In mass selection a large number of plants of similar phenotype or morphological characters are selected and their seeds are mixed together to constitute a new variety. The population obtained from the selected plants would be more uniform than the original population and are not individually tested. After repeated selection for about five to six years, selected seeds are multiplied and distributed to the farmers. The only disadvantage of mass selection is that it is difficult to distinguish the hereditary variation from environmental variation.

b. Pureline selection: Johannsen in 1903 coined the word pureline. It is a collection of plants obtained as a result of repeated self-pollination from a single homozygous individual. Hence, a variety formed by this method shows more homozygosity with respect to all genes. The disadvantage of this type is that the new genotypes are never created and they are less adaptable and less stable to the environmental fluctuations.

Figure 9.9: Mass selection vs Pureline selection

c. Clonal Selection: In asexually propagated crop, progenies derived from a plant resemble in genetic constitution with the parent plant as they are mitotically divided. Based on their phenotypic appearance, clonal selection is employed to select improved variety from a mixed population (clones). The selected plants are multiplied through vegetative propagation to give rise to a clone. The genotype of a clone remains unchanged for a long period of time.

Figure 9.10: Clonal Selection

9.6.3 Hybridization

Hybridization is the method of producing new crop varieties in which two or more plants of unlike genetically constitution is all crossed together that result in a progeny called hybrid. Hybridization offers improvement in crop and is the only effective means of combining together the desirable characters of two or more varieties or species. The first natural hybridization was observed by Cotton Mather in maize.

Steps in Hybridization

1. Selection of Parents: Male and female plants of the desired characters are selected. Both should be tested for their homozygosity.
2. Emasculation: It is a process of removal of anthers to prevent self pollination before dehiscence of anther.
3. Bagging: The stigma of the flower is protected against any undesirable pollen grains, by covering it with a bag.
4. Crossing: Transfer of pollen grains from selected male flower to the stigma of the female emasculated flower.
5. Harvesting seeds and raising plants: The pollination leads to fertilization and finally seed formation takes place. The seeds are grown into new generation which are called hybrids.

Figure 9.11 a & b: Emasculation and Bagging (Wheat)

Types of Hybridization

According to the relationship between plants, the hybridization is divided into:

1. Intravarietal hybridization – The cross between the plants of same variety. Such crosses are useful only in self-pollinated crops.

2. Intervarietal hybridization – The cross between the plants belonging to two different varieties of the same species and is also known as intraspecific hybridization. This technique has been the basis of improving self-pollinated as well as cross pollinated crops.

Figure 9.12: Flower – (a) G. hirsutum (b) G. arboretum

3. Interspecific hybridization – The cross between the plants belonging to different species belonging to the same genus is also called intragenic hybridization. It is commonly used for transferring the genes of disease, insect, pest and drought resistance from one species to another.

Example: Gossypium hirsutum x Gossypium arboreum – Deviraj.

4. Intergeneric hybridization – The crosses are made between the plants belonging to two different genera. The disadvantages are hybrid sterility, time consuming and expensive procedure.

Example: Raphanobrassica, Triticale. (Refer chapter 4 for detailed illustration)

9.6.4 Heterosis

Heterosis (hetero- different; sis - condition): G.H. Shull was the first scientist to use the term heterosis in 1912. The superiority of the F1 hybrid in performance over its parents is called heterosis or hybrid vigour. Vigour refers to increase in growth, yield, greater adaptability of resistance to diseases, pest and drought. Vegetative propagation is the best suited measure for maintaining hybrid vigour, since the desired characters are not lost and can persist over a period of time. Many breeders believe that the magnitude of heterosis is directly related to the degree of genetic diversity between the two parents.

Classification of Heterosis

Depending on the nature, origin, adaptability and reproducing ability heterosis can be classified as:

1. Euheterosis – This is the true heterosis which is inherited and is further classified as:

• a. Mutational Euheterosis – Simplest type of euheterosis and results from the sheltering or eliminating of the deleterious, unfavourable often lethal, recessive, mutant genes by their adaptively superior dominant alleles in cross pollinated crops.
• b. Balanced Euheterosis – Well balanced gene combination which is more adaptive to environmental conditions and agricultural usefulness.

2. Pseudoheterosis – Also termed as luxuriance. Progeny possess superiority over parents in vegetative growth but not in yield and adaptation, usually sterile or poorly fertile.

9.6.5 Mutation Breeding

Muller and Stadler (1927–1928) coined the term mutation breeding. It represents a new method of conventional breeding procedures as they have the advantage of improving the defect without losing agronomic and quality character in agriculture and crop improvement. Mutation means the sudden heritable changes in the genotype or phenotype of an organism. Gene mutations are of considerable importance in plant breeding as they provide essential inputs for evolution as well as for re-combination and selection. It is the only method for improving seedless crops.

Radiation such as UV short wave, X-ray, Alpha (α), Beta (β), Gamma waves and many chemicals such as cesium, EMS (ethyl methane sulfonate), nitromethylurea induce mutation to develop new varieties of crops.

Example: Triple gene dwarf wheat with increase in yield and height. Atomita 2 - rice with salinity tolerance and pest resistance.

9.6.6 Polyploid Breeding

Majority of flowering plants are diploid (2n). The plants which possess more than two sets of chromosome are called polyploids. Polyploidy is a major force in the evolution of both wild and cultivated plants. Polyploidy often exhibits increased hybrid vigour, increased heterozygosity, increase tolerance to both biotic and abiotic stresses, buffering of deleterious mutations. In addition, polyploidy often results in reduced fertility due to meiotic error allowing the production of seedless varieties.

When chromosome number is doubled by itself in the same plant, is called autopolyploidy.

Example: A triploid condition in sugarbeets, apples and pear has resulted in the increase in vigour and fruit size, large root size, large leaves, flower, more seeds and sugar content in them. It also resulted in seedless tomato, apple, watermelon and orange. Polyploidy can be induced by the use of colchicine to double the chromosome number.

Allopolyploids are produced by multiplication of chromosome sets that are initially derived from two different species.

Example: Triticale (Triticum durum x Secale cereale); Raphanobrassica (Brassica oleraceae x Raphanus sativus).

Do You Know?

Gamma Garden or Atomic Garden: Is a form of mutation breeding where plants are exposed to radioactive sources typically cobalt-60 or caesium-137 in order to generate desirable mutation in crop plants. The first Gamma garden in India is Bose Research Institute at Calcutta in 1959 and the second is IARI in 1960 which produced large variation in short type.

9.6.7 Green Revolution

Green revolution – the term was coined by William S. Gaud in (1968). It is defined as the cumulative result of a series of research, development, innovation and technology transfer initiatives. Agricultural production (especially wheat and rice) manifolds worldwide particularly in the developing countries between the 1940's and the late 1960's. The Green revolution or third Agricultural Revolution is the intensive plan of 1960's to increase crop yield in developing countries by introducing the high yielding, resistant varieties, increased irrigation facilities, fertilizer application and better agricultural management.

In 1963 semi-dwarf wheat of Mexico was introduced from which India got five prolonged strategies for breeding a wide range of high varieties like Sonora 64, Sonalika and Kalyansona possessing a broad spectrum of resistance to major biotic and abiotic condition. Same as wheat, M.S. Swaminathan produced the first semi-dwarf fertiliser responsive hybrid variety of rice TNI (Taichung Native-1) in 1956 from Taiwan. The derivatives were introduced in 1966. Later better yielding semi dwarf varieties of rice Jaya and Ratna developed in India.

Do You Know?

NORIN 10 – The cultivars found that Norin 10 dwarfing genes have high photosynthetic rate per unit leaf area and increase respiratory activity. Gonjiro Inazuka selected the semi-dwarf wheat variety that became Norin 10. He would have never thought that the semi dwarf genes would not only revolutionize the world of wheat but also helped to save more than one billion lives from hunger and starvation.

Plant Breeding for Developing Resistance to Diseases

Some crop varieties bred by hybridization and selection, for disease resistance to fungi, bacteria and viral diseases are released (Table 9.1).

Crop	Variety	Resistance to Diseases
Wheat	Himgiri	Leaf and Stripe rust, hill bunt
Brassica	Pusa swarnim (Kara rai)	White rust
Cauliflower	Pusa Shubhra, Pusa snowball K-1	Black rot and curl blight black rot
Cowpea	Pusa Komal	Bacterial blight
Chilli	Pusa Sadabahar	Chilly mosaic virus, Tobacco mosaic virus and Leaf curl

Table 9.2: Disease resistance varieties

Norman E. Borlaug

The plant pathologist plant breeder devoted his life at the International Maize and Wheat improvement centre at Sonord in Mexico. He developed a new high yielding, rust resistant, non-lodging dwarf wheat varieties like Norin-10, Sonora-64, Lerma rojo-64, etc. which are now being cultivated in many countries. This formed the base for 'green revolution'. He was awarded a Nobel prize for Peace in 1970.

Dr. M. S. Swaminathan

He is a pioneer mutation breeder. He has produced Sharbati Sonora, is the amber grain coloured variety of wheat by mutation, which is responsible for green revolution in India. Dr. Swaminathan is called "Father of green revolution in India".

Nel Jayaraman

Mr. Jayaraman, hails from Adirangam village in Tiruvarur district. He was a disciple of Dr. Nammalvar and state coordinator of 'Save our rice campaign, Tamil Nadu. He strived hard for conservation of traditional rice varieties. He had trained a team of farmers and regularly update them on the current issues that affect them. In 2005, he organized a first ever traditional paddy seed festival in his farm as an individual. The seed festival in May 2016 at Adhirangam was 10th in a row and in which 156 different traditional varieties were distributed to more than 7000 farmers across Tamil Nadu. He was invited by the Philippines Government to give a talk at the International Rice Research Institute (IRRI) on his work and mission. In 2011, he received the State Award for best organic farmer for his contribution to organic farming, and in the year 2015, he received the National Award for best Genome Savior.

Resistance to yellow mosaic virus in bhindi (Abelmoschus escullentus) was transferred from a wild species and resulted in a new variety of A. Escullentus called Parbharni kranti.

Plant Breeding for Developing Resistance to Insect Pests

Insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics. Hairy leaves in several plants are associated with resistance to insect pests.

Example: Resistance to jassids in cotton and cereal leaf beetle in wheat. In wheat, solid stems lead to non-preference by the stem sawfly and smooth leaves and nectar-less cotton varieties do not attract bollworms. High aspartic acid, low nitrogen and sugar content in maize leads to resistance to maize stem borers.

Crop	Variety	Insect Pests
Brassica (Rapeseed mustard)	Pusa Gaurav	Aphids
Flat bean	Pusa Sem 2, Pusa Sem 3	Jassids, aphids and fruit borer
Okra (Bhindi)	Pusa Sawani, Pusa A-4	Shoot and Fruit borer

Table 9.3: Pest resistance varieties

9.7 Modern Plant Breeding

In the milestones of plant breeding methods, Genetic Engineering, Plant tissue culture, Protoplasmic fusion or somatic hybridisation, Molecular marking and DNA finger printing are some of the modern plant breeding tools used to improve the crop varieties. We have already discussed about the various techniques and application of the above mentioned concepts in Unit 8.

New Plant Engineering Techniques / New Breeding Techniques (NBT)

NBT are a collection of methods that could increase and accelerate the development of new traits in plant breeding. These techniques often involve genome editing, to modify DNA at specific locations within the plants to produce new traits in crop plants. The various methods of achieving these changes in traits include the following:

• Cutting and modifying the genome during the repair process by tools like CRISPR/Cas.
• Genome editing to introduce changes in few base pairs using a technique called Oligonucleotide-directed mutagenesis (ODM).
• Transferring a gene from an identical or closely related species (cisgenesis).
• Organising processes that alter gene activity without altering the DNA itself (epigenetic methods).

Summary

Chapter Summary

• Economic Botany deals with the relationship between people and economically important plants to fulfill the three basic needs of life such as food, clothing and shelter.
• Domestication, a term often used for a more intricate process, involves the genetic alteration of plants which did not appear at once, but rather over a substantial period of time, perhaps hundreds of years for some species.
• In the history of agriculture Vavilov has given the eight main centres of origin of plants were now divided into 12 centres of origin.
• In Organic agriculture biofertilizers are microbial inoculants which are ecofriendly, more effective even though cost effective than chemical fertilizers. Rhizobium, Azolla, VAM and sea weeds are used as fertilizers which increase the crop yield many fold.
• Plant breeding is a purposeful manipulation of plant species in order to create desirable genotype and phenotype for the benefit of mankind.
• Plant introduction, selection, hybridization, heterosis, mutation breeding, polyploidy breeding and green revolution are the different methods of conventional breeding.

Evaluation

Exercise 1. Assertion and Reason

Assertion: Genetic variation provides the raw material for selection.

Reason: Genetic variations are differences in genotypes of the individuals.

a. Assertion is right and reason is wrong. b. Assertion is wrong and reason is right. c. Both reason and assertion is right. d. Both reason and assertion is wrong. Exercise 2. MCQ

2. While studying the history of domestication of various cultivated plants, _______ were recognized earlier.

a. Centres of origin b. Centres of domestication c. Centres of hybrid d. Centres of variation Exercise 3. MCQ

3. Pick out the odd pair.

a. Mass selection – Morphological characters b. Purline selection – Repeated self pollination c. Clonal selection – Sexually propagated d. Natural selection – Involves nature Exercise 4. Match the Following

Match Column 1 with Column 2:

Column 1	Column 2	Your Answer
1. William S. Gaud	1. Heterosis
2. Shull	2. Mutation breeding
3. Cotton Mather	3. Green revolution
4. Muller and Stadler	4. Natural hybridization

Exercise 5. MCQ

5. The quickest method of plant breeding is

a. Introduction b. Selection c. Hybridization d. Mutation breeding Exercise 6. MCQ

6. Desired improved variety of economically useful crops are raised by

a. Natural Selection b. hybridization c. mutation d. biofertilisers Exercise 7. MCQ

7. Plants having similar genotypes produced by plant breeding are called

a. clone b. haploid c. autopolyploid d. genome Exercise 8. MCQ

8. Importing better varieties and plants from outside and acclimatising them to local environment is called

a. cloning b. heterosis c. selection d. introduction Exercise 9. MCQ

9. Dwarfing gene of wheat is

a. pal 1 b. Atomita 1 c. Norin 10 d. pelita 2 Exercise 10. MCQ

10. Crosses between the plants of the same variety are called

a. interspecific b. inter varietal c. intra varietal d. inter generic Exercise 11. MCQ

11. Progeny obtained as a result of repeat self pollination in a cross pollinated crop is called

a. pure line b. pedigree line c. inbreed line d. heterosis Exercise 12. MCQ

12. Jaya and Ratna are the semi dwarf varieties of

a. wheat b. rice c. cowpea d. mustard Exercise 13. MCQ

13. Which one of the following are the species that are crossed to give sugarcane varieties with high sugar, high yield, thick stems and ability to grow in the sugarcane belt of North India?

a. Saccharum robustum and Saccharum officinarum b. Saccharum barberi and Saccharum officinarum c. Saccharum sinense and Saccharum officinarum d. Saccharum barberi and Saccharum robustum Exercise 14. Match the Following

Match Column 1 (Crop) with Column 2 (Corresponding disease resistant variety):

Column 1 (Crop)	Column 2 (Disease Resistant Variety)	Your Answer
1. Cowpea	1. Himgiri
2. Wheat	2. Pusa komal
3. Chilli	3. Pusa Sadabahar
4. Brassica	4. Pusa Swarnim

Exercise 15. MCQ

15. A wheat variety, Atlas 66 which has been used as a donor for improving cultivated wheat, which is rich in

a. iron b. carbohydrates c. proteins d. vitamins Exercise 16. MCQ

16. Which one of the following crop varieties correctly matches with its resistance to a disease?

a. Pusa Komal – Bacterial blight b. Pusa Sadabahar – White rust c. Pusa Shubhra – Chilli mosaic virus d. Brassica – Pusa swarnim Exercise 17. MCQ

17. Which of the following is incorrectly paired?

a. Wheat – Himgiri b. Milch breed – Sahiwal c. Rice – Ratna d. Pusa Komal – Brassica Exercise 18. Match List 1 with List 2

List 1 (Biofertilizer)	List 2 (Organisms)	Your Answer
1. Free living N₂	a. Aspergillus
2. Symbiotic N₂	b. Amanita
3. P Solubilizing	c. Anabaena azollae
4. P Mobilizing	d. Azotobacter

Exercise 19. Short Answer

19. Differentiate primary introduction from secondary introduction.

Exercise 20. Short Answer

20. How are microbial innoculants used to increase the soil fertility?

Exercise 21. Short Answer

21. What are the different types of hybridization?

Exercise 22. Short Answer

22. Explain the best suited type followed by plant breeders at present.

Exercise 23. Long Answer

23. Write a note on heterosis.

Exercise 24. Short Answer

24. List out the new breeding techniques involved in developing new traits in plant breeding.

Appendix

Glossary

Acclimatization (n) The adaptation of an individual to a changed climate or the adjustment of a species or a population to a changed environment over a number of generations. Agronomy (n) Science of farming. Germplasm Collection (n) The entire collection (of plants/seeds) having all the diverse alleles for all genes in a given crop is called germplasm collection. Non recurrent parent (n) The parent of a hybrid that is not again used as a parent in backcrossing. Quarantine (n) Strict isolation imposed to prevent the spread of disease. Strain (n) A group of similar individuals from a common origin.

Milestones in Plant Breeding

Biofortification

Biofortification – breeding crops with higher levels of vitamins and minerals or higher protein and healthier fats – is the most practical means to improve public health. Breeding for improved nutritional quality is undertaken with the objectives of improving:

• Protein content and quality
• Oil content and quality
• Vitamin content
• Micronutrient and mineral content

In 2000, maize hybrids that had twice the amount of amino acids, lysine and tryptophan, compared to existing maize hybrids were developed. Wheat variety, Atlas 66 having a high protein content, has been used as a donor for improving cultivated wheat. It has been possible to develop an iron fortified rice variety containing over five times as much iron as in commonly consumed varieties.

The Indian Agricultural Research Institute, New Delhi has also released several vegetable crops that are rich in vitamins and minerals, example: vitamin A enriched carrots, spinach, pumpkin; vitamin C enriched bitter gourd, bathua, mustard, tomato; iron and calcium enriched spinach and protein enriched beans – broad, lablab, French garden peas.

Sugar Cane

Saccharum barberi was originally grown in North India, but had poor sugar content and yield. Tropical canes grown in South India Saccharum officinarum had thicker stems and higher sugar content but did not grow well in North India. These two species were successfully crossed to get sugar cane varieties combining the desirable qualities of high yield, thick stems, high sugar and ability to grow in the sugarcane areas of North India.

ICT Corner – Plant Breeding

Let us know about the details of Medicinal Plants in detail.

Steps:

1. Type the URL or scan the QR code to open the activity page – then the Introduction page will open.
2. Click on 'Plants' – it will display list of Medicinal Plants.
3. Click on each plant individually – on the next screen it displays the description, harvesting and properties of the plants.
4. Click the option on the top left side of the front page to see the preparation of oils, Powder etc.

URL: https://play.google.com/store/apps/details?id=com.dssoft.plantasmedicinales

Book-back Exercises — Questions & Answers

Answers generated strictly from the Samacheer Kalvi textbook content. Attempt each question first, then click "Show Answer" to check.

I. Choose the Correct Answer

1. Assertion: Genetic variation provides the raw material for selection. Reason: Genetic variations are differences in genotypes of the individuals.

a) Assertion is right and reason is wrong. b) Assertion is wrong and reason is right. c) Both reason and assertion is right. d) Both reason and assertion is wrong.

Answer: c) Both reason and assertion is right.

Explanation: Genetic variation provides the raw material for selection in plant breeding, and genetic variations are indeed differences in genotypes of the individuals, making both the assertion and reason correct.

2. While studying the history of domestication of various cultivated plants _____ were recognized earlier.

a) Centres of origin b) Centres of domestication c) Centres of hybrid d) Centres of variation

Answer: a) Centres of origin

Explanation: In the history of agriculture, Vavilov identified the main centres of origin of plants, which were recognized while studying the history of domestication of various cultivated plants.

3. Pick out the odd pair.

a) Mass selection – Morphological characters b) Pureline selection - Repeated self pollination c) Clonal selection - Sexually propagated d) Natural selection - Involves nature

Answer: c) Clonal selection - Sexually propagated

Explanation: Clonal selection is employed in asexually propagated crops, not sexually propagated crops. Progenies derived from a plant resemble the parent in genetic constitution as they are mitotically divided.

4. Match Column 1 with Column 2.

Column 1	Column 2
1. William S. Gaud	1. Heterosis
2. Shull	2. Mutation breeding
3. Cotton Mather	3. Green revolution
4. Muller and Stadler	4. Natural hybridization

Answers: 1 – 3 (Green revolution), 2 – 1 (Heterosis), 3 – 4 (Natural hybridization), 4 – 2 (Mutation breeding)

5. The quickest method of plant breeding is

a) Introduction b) Selection c) Hybridization d) Mutation breeding

Answer: a) Introduction

Explanation: Plant introduction is the quickest method as it involves introducing genotypes from a place where they are normally grown to a new environment, requiring no breeding steps from scratch.

6. Desired improved variety of economically useful crops are raised by

a) Natural Selection b) hybridization c) mutation d) biofertilisers

Answer: b) hybridization

Explanation: Hybridization offers improvement in crop and is the only effective means of combining together the desirable characters of two or more varieties or species to raise desired improved varieties.

7. Plants having similar genotypes produced by plant breeding are called

a) clone b) haploid c) autopolyploid d) genome

Answer: a) clone

Explanation: In clonal selection, selected plants are multiplied through vegetative propagation to give rise to a clone. The genotype of a clone remains unchanged for a long period of time.

8. Importing better varieties and plants from outside and acclimatising them to local environment is called

a) cloning b) heterosis c) selection d) introduction

Answer: d) introduction

Explanation: Plant introduction is defined as the introduction of genotypes from a place where it is normally grown to a new place or environment. The adaptation of the introduced plant in the changed environment is called acclimatization.

9. Dwarfing gene of wheat is

a) pal 1 b) Atomita 1 c) Norin 10 d) pelita 2

Answer: c) Norin 10

Explanation: Gonjiro Inazuka selected the semi-dwarf wheat variety that became Norin 10. The Norin 10 dwarfing genes have high photosynthetic rate per unit leaf area and increased respiratory activity.

10. Crosses between the plants of the same variety are called

a) interspecific b) inter varietal c) intra varietal d) inter generic

Answer: c) intra varietal

Explanation: Intravarietal hybridization is the cross between the plants of the same variety. Such crosses are useful only in self-pollinated crops.

11. Progeny obtained as a result of repeat self pollination in a cross pollinated crop is called

a) pure line b) pedigree line c) inbreed line d) heterosis

Answer: a) pure line

Explanation: Pureline is a collection of plants obtained as a result of repeated self-pollination from a single homozygous individual. Johannsen coined the word pureline in 1903.

12. Jaya and Ratna are the semi dwarf varieties of

a) wheat b) rice c) cowpea d) mustard

Answer: b) rice

Explanation: Better yielding semi dwarf varieties of rice Jaya and Ratna were developed in India, following M.S. Swaminathan's production of the first semi-dwarf fertiliser responsive hybrid variety of rice TNI.

13. Which one of the following are the species that are crossed to give sugarcane varieties with high sugar, high yield, thick stems and ability to grow in the sugarcane belt of North India?

a) Saccharum robustum and Saccharum officinarum b) Saccharum barberi and Saccharum officinarum c) Saccharum sinense and Saccharum officinarum d) Saccharum barberi and Saccharum robustum

Answer: b) Saccharum barberi and Saccharum officinarum

Explanation: Saccharum barberi was grown in North India but had poor sugar content. Saccharum officinarum (tropical canes) had thicker stems and higher sugar content. These two species were successfully crossed to get varieties combining high yield, thick stems, high sugar and ability to grow in North India.

14. Match column 1 (crop) with column 2 (Corresponding disease resistant variety) and select the correct option from the given codes.

Column 1	Column 2
1. Cowpea	1. Himgiri
2. Wheat	2. Pusa komal
3. Chilli	3. Pusa Sadabahar
4. Brassica	4. Pusa Swarnim

Answers: 1 – 2 (Pusa Komal), 2 – 1 (Himgiri), 3 – 3 (Pusa Sadabahar), 4 – 4 (Pusa Swarnim)

15. A wheat variety, Atlas 66 which has been used as a donor for improving cultivated wheat, which is rich in

a) iron b) carbohydrates c) proteins d) vitamins

Answer: c) proteins

Explanation: Wheat variety Atlas 66, having a high protein content, has been used as a donor for improving cultivated wheat as part of biofortification efforts.

16. Which one of the following crop varieties correctly matches with its resistance to a disease?

a) Pusa Komal – Bacterial blight b) Pusa Sadabahar – White rust c) Pusa Shubhra – Chilli mosaic virus d) Brassica – Pusa swarnim

Answer: a) Pusa Komal – Bacterial blight

Explanation: According to the disease resistance varieties table, Cowpea variety Pusa Komal is resistant to Bacterial blight.

17. Which of the following is incorrectly paired?

a) Wheat - Himgiri b) Milch breed - Sahiwal c) Rice - Ratna d) Pusa Komal - Brassica

Answer: d) Pusa Komal - Brassica

Explanation: Pusa Komal is a disease-resistant variety of Cowpea (not Brassica). Pusa Swarnim is the disease-resistant variety associated with Brassica.

18. Match list 1 with list 2.

List 1 – Biofertilizer	List 2 – Organisms
1. Free living N₂	a. Aspergillus
2. Symbiotic N₂	b. Amanita
3. P Solubilizing	c. Anabaena azollae
4. P Mobilizing	d. Azotobactor

Answers: 1 – d (Azotobacter: free living nitrogen fixer), 2 – c (Anabaena azollae: symbiotic nitrogen fixer with Azolla), 3 – a (Aspergillus: phosphate solubilizing), 4 – b (Amanita: phosphate mobilizing/mycorrhizae)

IV. Answer Briefly

19. Differentiate primary introduction from secondary introduction.

Answer: In Primary introduction, the introduced variety is well adapted to the new environment without any alteration to the original genotype. In Secondary introduction, the introduced variety is subjected to selection to isolate a superior variety and hybridized with a local variety to transfer one or a few characters to them.

20. How are microbial inoculants used to increase the soil fertility?

Answer: Biofertilizers are preparations containing living or latent cells of efficient strains of micro-organisms. They are efficient in fixing nitrogen, solubilising phosphate and decomposing cellulose. They improve soil fertility, plant growth, and increase the number and biological activity of beneficial microorganisms in the soil. They are eco-friendly and more cost-effective than chemical fertilizers. Examples include Rhizobium, Azolla, Arbuscular mycorrhizae, and Seaweed liquid fertilizer.

21. What are the different types of hybridization?

Answer: The different types of hybridization are: (1) Intravarietal hybridization – cross between plants of the same variety, useful in self-pollinated crops. (2) Intervarietal hybridization – cross between plants of two different varieties of the same species. (3) Interspecific hybridization – cross between plants of different species of the same genus; used for transferring disease and pest resistance genes. Example: Gossypium hirsutum × Gossypium arboreum. (4) Intergeneric hybridization – crosses between plants of two different genera. Example: Raphanobrassica, Triticale.

22. Explain the best suited type followed by plant breeders at present?

Answer: The best suited type followed by plant breeders at present is Intervarietal hybridization. It involves the cross between plants belonging to two different varieties of the same species (intraspecific hybridization). This technique has been the basis of improving both self-pollinated and cross-pollinated crops. It combines desirable characters from two or more varieties effectively, making it widely used in modern plant breeding programs.

V. Answer in Detail

23. Write a note on heterosis.

Answer: G.H. Shull was the first scientist to use the term heterosis in 1912. The superiority of the F1 hybrid in performance over its parents is called heterosis or hybrid vigour. Vigour refers to increase in growth, yield, greater adaptability, and resistance to diseases, pest and drought. Vegetative propagation is the best suited measure for maintaining hybrid vigour, since desired characters are not lost and can persist over time. Many breeders believe that the magnitude of heterosis is directly related to the degree of genetic diversity between the two parents. Heterosis is classified as: (1) Euheterosis – true inherited heterosis, further divided into (a) Mutational Euheterosis – simplest type, results from sheltering deleterious recessive mutant genes by dominant alleles, and (b) Balanced Euheterosis – well balanced gene combination adaptive to environment and agriculture. (2) Pseudoheterosis (luxuriance) – progeny shows superiority in vegetative growth but not in yield; usually sterile or poorly fertile.

24. List out the new breeding techniques involved in developing new traits in plant breeding.

Answer: New Breeding Techniques (NBT) are a collection of methods that increase and accelerate the development of new traits in plant breeding. These techniques often involve genome editing to modify DNA at specific locations. The various methods include: (1) Cutting and modifying the genome during the repair process by tools like CRISPR/Cas. (2) Genome editing to introduce changes in few base pairs using a technique called Oligonucleotide-directed mutagenesis (ODM). (3) Transferring a gene from an identical or closely related species (cisgenesis). (4) Organising processes that alter gene activity without altering the DNA itself (epigenetic methods). These techniques, along with Genetic Engineering, Plant tissue culture, Protoplasmic fusion/somatic hybridisation, Molecular marking and DNA fingerprinting, are modern plant breeding tools used to improve crop varieties.

📝 Summary

1. Economic botany studies the relationship between people and economically important plants, exploring how humans use plants for food, medicines, and other uses, intersecting fields like agronomy, anthropology, archaeology, chemistry, trade and commerce.
2. Domestication is the process of bringing a plant species under human control through careful selection, genetic alteration, and handling, leading to changes such as increased yield, increased fruit and seed size, seedless parthenocarpic fruit, and resistance to disease and pests.
3. The earliest archaeological evidence of agriculture is found in the fertile crescent region around the Tigris and Euphrates river valleys, approximately 12,000 years ago, with early Greek and Roman naturalists like Theophrastus and Pliny the Elder contributing to understanding plant domestication.
4. Organic farming is an alternative agricultural system that originated in the early twentieth century, relying on ecological processes, biodiversity, and cycles adapted to local conditions rather than inputs with adverse effects, sustaining the health of soils, ecosystems, and people.
5. Biofertilizers contain living or latent cells of efficient micro-organism strains that fix nitrogen, solubilise phosphate, and decompose cellulose; they are eco-friendly, cost-effective alternatives to chemical fertilizers that improve soil fertility and plant growth.