Plant Breeding

Class 12 | Pure Science — Botany | Chapter 9

Class 12 Unit 9 Pure_Science

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.

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.
• Realize the importance of seed protection and seed storage.
• Compare the traditional methods of seed storage with modern methods.

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
• 9.8 Seed protection
• 9.9 Seed storage

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 parthenocarpy fruit.
• Enhancing colour, appearance, palatability and nutritional composition.

9.3 Origin of Agriculture

Archaeological 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

Biofertilizers are defined as preparations containing living cells or latent cells of efficient strains of microorganisms 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

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

Table 9.1: Classification of Biofertilizers

Group	Type	Examples
A. N₂ Fixing Biofertilizers	Free-living	Azotobacter, Clostridium, Anabaena, Nostoc
	Symbiotic	Rhizobium, Anabaena azollae
	Associative Symbiotic	Azospirillum
B. P Solubilizing Biofertilizers	Bacteria	Bacillus subtilis, Pseudomonas striata
	Fungi	Penicillium, Aspergillus
	Arbuscular Mycorrhiza	Glomus, Scutellospora
C. P Mobilizing Biofertilizers	Ectomycorrhiza	Amanita
D. Biofertilizer for Micro nutrients	Silicate and Zinc solubilizers	Bacillus
E. Plant Growth Promoting Rhizobacteria	Pseudomonas	Pseudomonas fluorescens

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%.

Azolla

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

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. 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. Liquid seaweed fertilizer is not only organic but also eco-friendly. The alginates in the seaweed that reacts with metals in the soil and form long, cross-linked polymers in the soil. These polymers improve the crumbing in the soil, swell up when they get wet and retain moisture for a long time. They are especially 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.

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 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 and (5) uptake and use of nutrients.
• 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. The most important green manure crops are Crotalaria juncea, Tephrosia purpurea, Indigofera tinctoria.

The green manuring can be practised as Green in-situ manuring or green leaf manuring. 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. Whereas green leaf manuring is 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.

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 thermo-sensitive varieties.

9.5.2 Steps in Plant Breeding

The main steps in plant breeding are:

1. Collection of variability
2. Evaluation and selection of parents
3. Cross hybridization among the selected parents
4. Selection and testing of superior recombinants
5. Testing, release and commercialization of new cultivars

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 alteration 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 been 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.
• 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.

9.6.3 Hybridization

Hybridization is the method of producing new crop varieties in which two or more plants of unlike genetically constitution are 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. It should be tested for their homozygosity.
2. Emasculation: It is a process of removal of anthers to prevent self-pollination before dehiscence of another.
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.

Types of Hybridization

1. Intervarietal 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.
3. Interspecific hybridization – The cross between the plants belonging to different species belonging to the same genus, 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 × 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.

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

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.

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.

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.

Examples:

• 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 chromosomes 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 × Secale cereale), Raphanobrassica (Brassica oleraceae × Raphanus sativus).

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 1960s. 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, bacterial and viral diseases are released (Table 9.2).

Crop	Variety	Resistance to diseases
Wheat	Himgiri	Leaf and Stripe rust, hill bunt
Brassica	Pusa swarnim (Karan 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

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

Do You Know?

Sugar cane: Saccharum bareri 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.

Norman E. Borlaug

The plant pathologist and plant breeder devoted his life at the International Maize and Wheat improvement centre at Sonora in Mexico. He developed 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.

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.

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).

9.8 Seed Protection

Seed is one of the most crucial elements in the livelihoods of agricultural communities. It is the repository of the genetic information of crop species and their varieties resulting from the continuous improvement and selection over the time. The potential benefits of seed to crop productivity and food security can be enormous. Crop protection products can be applied during the growth of the crop or added to the seed. Seed protection play a significant role in improving the establishment of healthy crops. Protection and storage of seeds can be done by traditional and modern methods.

9.8.1 Traditional Methods of Seed Protection

• In traditional method seeds are coated with fine red soil, Guntur Chilli Powder, Neem leaf Powder, Powder of Bittergourd, Drumstick extract, Pongamia leaf extract and stored for short duration.
• Paddy Seeds are immersed in salt water in the ratio of 1:10 to remove the floating chaffy seed and then dried in shade for one–two years of storage.
• Sorghum seeds were treated with lime water (1 kg of lime in 10 litres of water) for 10 days and then the seeds are dried and stored.
• Chickpea were treated with citronella leaf oil, cotton seed oil, soya bean oil, castor seed oil (500 ml of oil for 100 kg of seed).
• Sunflower seeds were kept inside the dried fruit of sponge gourd after removing the seeds. These fruits were kept in an airtight container.

9.8.2 Modern Methods of Seed Protection

1. Seed Treatment

In agriculture and horticulture, seed treatment or seed dressing is a chemical, typically antimicrobial or antifungal, with which seeds are treated (or dressed) prior to planting.

Benefits of seed treatment:

• Prevents spread of plant disease.
• Protects seed from seedling blights.
• Improves germination.
• Provides protection from storage insects.
• Controls soil insects.

2. Seed Hardening

Seed hardening is a physiological preconditioning of the seed by soaking of seed in water or chemical solution for definite duration in proper ratio (Seed:Solution) and shade drying to bring back the seed to original moisture content.

Benefits:

• It increases the yield, root growth and vigour of seed germination.
• The uniformity of seedling emergence.
• Flowering occurs 2-3 days earlier.
• Uniform seed set and maturity.
• Exposes the seed to drought tolerance.

3. Seed Pelleting

The process of enclosing seed in a filter inert material using an adhesive with bioactive chemicals. Seed pelleting increases the weight, size and shape of seeds by allowing precise maturing and spacing of seed in the field.

4. Seed Coating

Seed coating is a thicker form of covering of seed and may contain fertilizer, growth promoters, rhizobium inoculum, nutritional elements and repulsive agents. Chemical, pesticides added to the seed by adhesive agents cause increased seed performance and seed germination.

5. Bio Priming of Seeds

Bio-Priming is a process of biological seed treatment that refers to combination of seed hydration (physiological aspect of disease control) and inoculation (biological aspect of disease control) of seed with beneficial organism to protect seed. It is an ecological approach using selected fungal antagonists against the soil and seed borne pathogens. This seed treatment may provide an alternative to chemical control.

9.9 Seed Storage

Storage starts in the mother plant itself when it attains physiological maturity. Storage may be defined as the preservation of viable seeds from the time of collection until they are required for sowing. After harvesting the seeds are either stored in ware houses or in transit or in retail shop.

9.9.1 Classification of Seeds Based on Storage

Type	Characteristics
Orthodox seeds	Can be dried to low moisture content and stored at low temperature for long periods
Recalcitrant seeds	Cannot withstand desiccation or low temperature; must be kept moist and at warm temperatures
Intermediate seeds	Can tolerate some desiccation but are damaged by very low temperatures

9.9.2 Methods of Seed Storage

1. Conventional Methods of Seed Storage

Conventional storage includes storage in Bamboo structure, mud and earthen structure, wooden structure and underground structure. In village level storage is done in large level in concrete/cement silos, Metal or plastic drums and metal silos. Improved rural level storage structure includes storage in coal tar drum, udaipur bin, bamboo bin, pusa bin and metal bins.

2. Modern Methods of Seed Storage

a. Seed storage in cryopreservation: It is the technique of germplasm conservation (storage of cells, tissue, embryo or seeds) by ultra-low temperature in liquid nitrogen at –196°C. It is not practical for commercial seed storage purpose, but is useful to store the valuable germplasm for use in future which cannot be preserved by conventional methods.

b. Seed storage in gene bank: In gene bank, seed storage is the preservation of seed under controlled environmental condition which will prolong the viability of the seeds for long periods. The temperature, relative humidity and seed moisture content, containers and distribution arrangement vary for each and every type of seed.

c. Svalbard seed bank: The seeds are stored in four ply sealed envelopes, and then placed into plastic tote containers on metal shelving racks. The storage rooms are kept at –18°C. The low temperature and limited access to O₂ will ensure low metabolic activity and delayed seed ageing. The permafrost surrounding will help to maintain low temperature of the seed when the electricity supply fails.

Do You Know?

Nanotechnology in Agriculture: Currently nanotechnology provides different nano devices and nano material that have a unique role in agriculture. For example, Nano biosensors to detect moisture content and nutrient status in the soil. Nanotechnology can offer Nano-fertilizers for efficient nutrient management, Nanoherbicides for selective weed control in crop field, Nanonutrient particles to increase seed vigor, Nano-pesticides for efficient pest management. Hence, nanotechnology have greater role in crop production with environmental safety, ecological sustainability and economic stability.

9.9.3 Seed Certification

Seed certification is a legally sanctioned system for quality control of seed multiplication and production. The purpose of this certification is to maintain the seeds and make them available to the public. Through certification, high quality seeds and propagating materials of notified kind and variety are grown and distributed to ensure genetic identity and purity.

Vavilov's Centre of Crop Origin

S.No.	Centre	Crops Domesticated
1	China	Foxtail millet, soybean, bamboo, onion, crucifers
2	India	Rice, sugarcane, mango, orange, eggplant, sesame
3	South East Asia	Rice, banana, coconut, clove, hemp
4	Central East	Wheat, pea, hemp, cotton etc.
5	The Near East	Wheat, rye, many subtropical and tropical fruits
6	Mediterranean	Olive, vegetables, oil yielding plants, wheats
7	Ethiopia (Abyssinian)	Wheat, barley, sesame, castor, coffee
8	Mesoamerica (South Mexican & Central American Centre)	Maize, bean, sweet potato, papaya, guava, tobacco
9	South America	Tomato, pineapple
10	The Chiloe Centre	Potato
11	The Brazilian–Paraguayan Centre	Groundnut, cashew nut, pineapple, peppers, rubber

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.

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 which are now divided into 12 centres of origin.
• In Organic agriculture biofertilizers are microbial inoculants which are eco-friendly, more effective even though cost effective than chemical fertilizers. Rhizobium, Azolla, VAM and sea weeds are used as fertilizers which increase the crop yield manyfold.
• 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.
• Seed is an important part of the plant as it gives the food for future generation, so it should be carefully protected and stored.
• Seed hardening, seed treatment, seed pelleting, seed coating and bio priming of seeds are the modern methods of seed protection.
• Seeds are stored in bamboo structure, mud or earthen structure in conventional method of storage. In villages, the farmers store the entire seeds in concrete/cement silos or metal or plastic drums.
• In modern methods of storage, we have cryo preservation, gene bank and Svalbard seed bank for long time seed storage.

Evaluation

Exercise MCQ Questions

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.

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

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

4. Match Column I with Column II:

Column I	Column II
i) William S. Gaud	I) Heterosis
ii) Shull	II) Mutation breeding
iii) Cotton Mather	III) Green revolution
iv) Muller and Stadler	IV) Natural hybridization

a) i–I, ii–II, iii–III, iv–IV b) i–III, ii–I, iii–IV, iv–II c) i–IV, ii–II, iii–I, iv–IV d) i–II, ii–IV, iii–III, iv–I

5. The quickest method of plant breeding is

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

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

a) Natural Selection b) Hybridization c) Mutation d) Biofertilisers

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

a) Clone b) Haploid c) Autopolyploid d) Genome

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

a) Cloning b) Heterosis c) Selection d) Introduction

9. Dwarfing gene of wheat is

a) Pal 1 b) Atomita 1 c) Norin 10 d) Pelita 2

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

a) Interspecific b) Intervarietal c) Intravarietal d) Intergeneric

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

a) Pure line b) Pedigree line c) Inbreed line d) Heterosis

12. Jaya and Ratna are the semi dwarf varieties of

a) Wheat b) Rice c) Cowpea d) Mustard

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

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

Column I	Column II
I. Cowpea	i) Himgiri
II. Wheat	ii) Pusa komal
III. Chilli	iii) Pusa Sadabahar
IV. Brassica	iv) Pusa Swarnim

a) iv iii ii i b) ii i iii iv c) ii iv i iii d) i iii iv ii

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

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

17. Which of the following is incorrectly paired?

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

18. Match List I with List II

List I (Biofertilizer)	List II (Organisms)
i) Free living N₂	a) Aspergillus
ii) Symbiotic N₂	b) Amanita
iii) P Solubilizing	c) Anabaena azollae
iv) P Mobilizing	d) Azotobacter

a) i–c, ii–a, iii–b, iv–d b) i–d, ii–c, iii–a, iv–b c) i–a, ii–c, iii–b, iv–d d) i–b, ii–a, iii–d, iv–c Exercise Short Answer Questions

19. List the ways by which seeds can be stored for longer duration.

20. Differentiate primary introduction from secondary introduction.

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

22. Discuss the importance of neem in seed storage.

23. What are the different types of hybridization?

Exercise Long Answer Questions

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

25. Write a note on heterosis.

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

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. Certified seed (n) Seed produced from the foundation or certified seed under the regulation of a legally constituted agency. 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. Pure-Line (n) Progeny of a single self-fertilised homozygous individual. Quarantine (n) Strict isolation imposed to prevent the spread of disease. Strain (n) A group of similar individuals from a common origin.

ICT Corner

Steps:

• Type the URL or scan the QR code to open the activity page then Introduction page will open.
• Click on 'Plants' it will display list of Medicinal Plants.
• Click on each plant individually on the next screen it displays the description, harvesting and properties of the plants.
• 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 variations are differences in genotypes of individuals and such variations provide the raw material for selection in plant breeding.

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: Vavilov gave eight main centres of origin of plants which are now divided into 12 centres of origin, recognized while studying the history of domestication of 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 ones. The selected plants are multiplied through vegetative propagation to give rise to a clone.

4. Match Column I with Column II.

Column I	Column II
i) William S. Gaud	I) Heterosis
ii) Shull	II) Mutation breeding
iii) Cotton Mather	III) Green revolution
iv) Muller and Stadler	IV) Natural hybridization

a) i–I, ii–II, iii–III, iv–IV b) i–III, ii–I, iii–IV, iv–II c) i–IV, ii–II, iii–I, iv–IV d) i–II, ii–IV, iii–III, iv–I

Answer: b) i–III, ii–I, iii–IV, iv–II

Explanation: William S. Gaud coined the term Green Revolution (1968); G.H. Shull first used the term Heterosis (1912); Cotton Mather observed the first natural hybridization in maize; Muller and Stadler (1927–1928) coined the term 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 involves introducing genotypes from a place where they are normally grown to a new environment, making it the quickest method as no breeding procedures are needed.

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 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, and the adjustment 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: Norin 10 is the semi-dwarf wheat variety; Gonjiro Inazuka selected it and the semi-dwarf genes from Norin 10 revolutionized the world of wheat and helped save billions from hunger.

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

a) interspecific b) intervarietal c) intravarietal d) intergeneric

Answer: c) intravarietal

Explanation: Intervarietal hybridization (intravarietal) refers to the cross between the plants of the same variety, and such crosses are useful only in self-pollinated crops.

11. Progeny obtained as a result of repeated 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, and a variety formed by this method shows more homozygosity.

12. Jaya and Ratna are the semi dwarf varieties of

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

Answer: b) rice

Explanation: M.S. Swaminathan produced the first semi-dwarf fertiliser responsive hybrid variety of rice TNI in 1956, and later better yielding semi-dwarf varieties of rice Jaya and Ratna were developed in India.

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 originally grown in North India but had poor sugar content, while Saccharum officinarum (tropical canes of South India) 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 I (crop) with column II (Corresponding disease resistant variety) and select the correct option from the given codes.

Column I	Column II
I. Cowpea	i) Himgiri
II. Wheat	ii) Pusa komal
III. Chilli	iii) Pusa Sadabahar
IV. Brassica	iv) Pusa Swarnim

a) iv iii ii i b) ii i iii iv c) ii iv i iii d) i iii iv ii

Answer: c) I–ii, II–i, III–iii, IV–iv

Explanation: From the chapter: Cowpea–Pusa Komal (bacterial blight), Wheat–Himgiri (leaf and stripe rust, hill bunt), Chilli–Pusa Sadabahar (chilly mosaic virus, tobacco mosaic virus and leaf curl), Brassica–Pusa Swarnim (white rust).

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 objectives to improve protein content and quality.

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 – (no match given)

Answer: a) Pusa Komal – Bacterial blight

Explanation: According to the disease resistance varieties table in the chapter, Cowpea variety Pusa Komal is resistant to Bacterial blight. Pusa Sadabahar (Chilli) is resistant to chilly mosaic virus; Pusa Shubhra (Cauliflower) is resistant to black rot and curl blight; Pusa Swarnim (Brassica) is resistant to white rust.

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 of Brassica, as given in Table 9.2 of the chapter.

18. Match List I with List II.

List I – Biofertilizer	List II – Organisms
i) Free living N₂	a) Aspergillus
ii) Symbiotic N₂	b) Amanita
iii) P Solubilizing	c) Anabaena azollae
iv) P Mobilizing	d) Azotobacter

a) i-c, ii-a, iii-b, iv-d b) i-d, ii-c, iii-a, iv-b c) i-a, ii-c, iii-b, iv-d d) i-b, ii-a, iii-d, iv-c

Answer: b) i-d, ii-c, iii-a, iv-b

Explanation: From the classification of biofertilizers table: Free-living N₂ fixing – Azotobacter; Symbiotic N₂ (Azolla) – Anabaena azollae; P Solubilizing fungi – Aspergillus; P Mobilizing Ectomycorrhiza – Amanita.

IV. Answer Briefly

19. List the ways by which seeds can be stored for longer duration.

Answer: Seeds can be stored for longer duration by the following modern methods: (i) Seed storage in cryopreservation – germplasm is stored at ultra-low temperature in liquid nitrogen at –196°C; (ii) Seed storage in gene bank – seeds are preserved under controlled environmental conditions of temperature, relative humidity and seed moisture content to prolong viability; (iii) Svalbard seed bank – seeds are stored in four-ply sealed envelopes placed in plastic tote containers on metal shelving racks and rooms are kept at –18°C, ensuring low metabolic activity and delayed seed ageing.

20. 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 or is hybridized with a local variety to transfer one or a few desirable characters to them. Thus, primary introduction requires no modification while secondary introduction involves selection or hybridization.

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

Answer: Biofertilizers are preparations containing living or latent cells of efficient strains of microorganisms. When applied through seed or soil, they help crop plants in nutrient uptake through interactions in the rhizosphere. They are efficient in fixing atmospheric nitrogen (e.g., Rhizobium, Azolla with Anabaena azollae), solubilizing phosphate (e.g., Bacillus subtilis, Aspergillus) and decomposing cellulose. They improve soil fertility, plant growth and the number and biological activity of beneficial microorganisms in the soil.

22. Discuss the importance of neem in seed storage.

Answer: In traditional methods of seed protection, Neem leaf powder is used to coat seeds before storage for short duration. Neem is also one of the important plant species useful for green leaf manure (Azadirachta indica). The use of neem leaf powder as a seed coating agent helps protect seeds from storage insects and pests in an eco-friendly and cost-effective manner without the use of synthetic chemicals.

23. What are the different types of hybridization?

Answer: According to the relationship between plants, hybridization is divided into four types: (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 (intraspecific hybridization), used for improving self- and cross-pollinated crops; (3) Interspecific hybridization – cross between plants of different species of the same genus (intragenic hybridization), used for transferring disease and drought resistance genes; (4) Intergeneric hybridization – cross between plants of two different genera, e.g., Raphanobrassica and Triticale.

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

Answer: Modern plant breeders use New Breeding Techniques (NBT), which are a collection of methods that increase and accelerate the development of new traits. These techniques often involve genome editing to modify DNA at specific locations within plants. The methods include: (i) CRISPR/Cas tools for cutting and modifying the genome during the repair process; (ii) Oligonucleotide-directed mutagenesis (ODM) for introducing changes in few base pairs; (iii) Cisgenesis for transferring a gene from an identical or closely related species; and (iv) Epigenetic methods that alter gene activity without altering the DNA itself. These NBTs along with Genetic Engineering, Tissue Culture and Molecular Marking are the best suited modern tools used by plant breeders at present.

25. 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, pests and drought. Many breeders believe the magnitude of heterosis is directly related to the degree of genetic diversity between two parents. Vegetative propagation is best suited for maintaining hybrid vigour. Heterosis is classified as Euheterosis (true hereditary heterosis — further divided into Mutational Euheterosis and Balanced Euheterosis) and Pseudoheterosis (luxuriance — progeny superior in vegetative growth but not in yield, usually sterile or poorly fertile).

26. 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. The various methods include: (i) Cutting and modifying the genome during the repair process by tools like CRISPR/Cas; (ii) Genome editing to introduce changes in few base pairs using Oligonucleotide-directed mutagenesis (ODM); (iii) Transferring a gene from an identical or closely related species (cisgenesis); (iv) Organising processes that alter gene activity without altering the DNA itself (epigenetic methods). These techniques often involve genome editing to modify DNA at specific locations within plants to produce new traits in crop plants.

📝 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 of plants is the process of bringing a plant species under human control through careful selection, genetic alteration, and handling, resulting in changes such as increased yield, uniform fruiting, increased fruit/seed size, and enhanced nutritional composition.
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 Greek and Roman naturalists like Theophrastus and Pliny the Elder laying scientific foundations for understanding cultivated plants.
4. Organic farming is an alternative agricultural system that originated in the early twentieth century, relying on ecological processes, biodiversity, and local conditions rather than inputs with adverse effects, to sustain the health of soils, ecosystems, and people.
5. Biofertilizers are preparations containing living or latent cells of efficient microorganism strains that help crop plants uptake nutrients in the rhizosphere; they fix nitrogen, solubilise phosphate, decompose cellulose, and are eco-friendly, cost-effective alternatives to chemical fertilizers.