Prasanna

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Modern Plant Breeding Techniques

In the milestones of plant breeding methods Genetic Engineering, Plant tissue culture, Protoplasmic fusion or somatic hybridisation, Molecular marking and DNA figer 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 VIII.

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).

Plant breeding is an activity that has been carried out since humans first started undertaking settled farming, but its scientific basis was only firmly established with the rediscovery of Mendel’s work on genetics at the end of the nineteenth century.

The impetus and sophistication of plant breeding have advanced at a tremendous pace over the last 30 years with the implementation of the new biotechnological possibilities. However, plant breeding itself is still necessarily based on sound genetics, experimental design, and traditional evaluation of phenotypes.

The strategies therefore underlying the practice of plant breeding are therefore not only relevant but necessary in order to carry out a successful plant breeding program. The basis for such plant breeding practices is set out in this article.

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Various Types Of Organic Agriculture | Biofertilizers

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.

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 ecofriendly organic agro inputs and are more efficient and cost effective than chemical fertilizers.

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 fies 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-flating water fern that fies the atmospheric nitrogen in association with nitrogen fiing blue green alga Anabaena azolla. It is used as a bio-fertilizer for wetland rice cultivation and is known to contribute 40 – 60 kg/ha/crop. The agronomic potential of Azolla is quite signifiant particularly for increasing the yield of rice crop, as it quickly decompose 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. 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, 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 affcting the plant health and growth. It also controls damping of 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.

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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. In this chapter we will discuss about some of the conventional methods of plant breeding.

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. Introduction may be classifid as Primary introduction and Secondary 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.

Selection

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

(i) Natural Selection:

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

(ii) Artifiial 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.

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

Steps involved in hybridization are as follows.

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 flwer 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

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

(i) Intravarietal hybridization:
The cross between the plants of same variety. Such crosses are useful only in self-pollinated crops.

(ii) 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.

(iii) 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.

(iv) 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).

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

(i) 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.

(ii) Pseudoheterosis:

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

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.

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).

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 fie 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.

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)

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.

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Plant Breeding and Its Various Steps and Objectives

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.

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.

Steps in Plant Breeding:

The main steps in plant breeding are given below

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History Of Agriculture

There are unique opportunities that plant breeding and agriculture offer the historian of biology, and unique ways in which the historian of biology can inform the history of plant breeding and agriculture (Harwood, 2006. Phillips and Kingsland, 2015).

There are also of course questions and challenges that the study of agricultural sites share with the study of other biological sites, such as those in medicine (Wilmot 2007. Woods et al. 2018), the environment (Agar and Ward 2018), and non-agricultural industries (Bud 1993).

Indeed, in some instances the agricultural, medical, environmental, and biologically industrial will be one and the same. This is to say nothing of what agricultural sites share in common with histories of science beyond biology, but that is a broader discussion I can only mention in passing (Parolini 2015).

This chapter will first address what agriculture has in common with themes that cut across this handbook, before turning in Part 2 to issues, problems, and questions that stem from agriculture’s particular features, ending in Part 3 with paths for future work.

The chapter therefore treats the intersection of biology and agriculture as demanding its own integrated attention, the two parts making up a larger historiographical whole. There are a number of reasons to give agricultural sciences and technologies this kind of autonomy from the historiography of biology at large.
First, it reminds us to question the nature, direction, and extent of influence that biological science and agriculture have had on one another.

Second, it promotes a more symmetric understanding of the knowledges that have mattered for biological science and agriculture. This is particularly important because so much of the history of biological science in agriculture has been about establishing the authority of scientific expertise over agriculture, often in competition with other kinds of expertise distributed throughout farming.

If we did not approach agricultural contexts symmetrically we might end up recapitulating the very arguments we are meant to be analysing. Third, it establishes a healthier and more distant vantage point for the historian, keeping the existing historiography of biology at arms length, allowing us to better observe its deficiencies and assumptions.

Aside from giving autonomy to the agricultural in histories of biology, there is another broad historiographical point to make. Historians of biology and agriculture have to strike a balance between which historiographical lineage they dedicate their work to, or indeed, whether they see themselves contributing to both histories of biology and agriculture simultaneously.

In some respects this issue is itself unique to agriculture, for if we look at the other topics in this handbook only one or two other chapters are asked to compete with completely different sets of scholarly lineages in their telling, these including Tracy Teslo on Race and Ethnicity, Marsha Richmond on Women, and Ana Barahona on the transnational.

Yes, other kinds of historian and scholar may make important interventions on the history of eugenics, Darwinism, and biotechnology, but when it comes to these topics nobody is in a position to outbid the historian of biology.

Agriculture is different, both in content, thanks to the variety of experts that it enrols across a very wide range of potential specialist areas, and also in terms of the historiographical landscape in which it sits, because agriculture has indeed belonged to whole other kinds of historian, be they social historians, economic historians, or historians of agriculture and the environment.

Ultimately all my talk of ownership and bidding is petty, and of course even in those topics that seem primarily the concern of the historian of biology other historical traditions and branches of scholarship are constantly being drawn in.

What I mean to convey is that: historians of biology have been late to agriculture; their insights have not always been understood as relevant or complementary to the history of agriculture; historians of agriculture seem to be getting on all too well without the historian of biology; and that if the recent growth in interest amongst historians of science into the agricultural is to be maintained and consolidated then interdisciplinary awareness is essential.

Here historians of biology offer a suite of valuable opportunities for historians of agriculture, be it through all the techno-imagining that goes into broader agricultural debate, or the chance to rethink social and economic relations on the farm, the meanings embodied in agricultural spaces, organisms, and communal practices, or as Jonathan Harwood has so brilliantly shown, through the issue of global food security (Harwood 2012).

But agriculture also demands a sensitivity and humility from the historian of biology, to know when multiple epistemologies are in play, multiple historiographies, and therefore how to translate any new historical understanding into a form that matters for defined audiences. These audiences should include not only historians of science but also those working on and in agricultural industries.