Plant And Animal Breeding
With exploding population all around the world, higher food production is a major necessity. Scientists from Bio-sciences have been engaged in bringing scientific principles in animal husbandry, plant breeding etc to agriculture field and enhancing output of the meat, dairy and plant-based food.
Traditional farming can only yield a limited biomass, as food for humans and animals. Better management practices and increase in acreage can increase yield, but only to a limited extent. Plant breeding as a technology has helped increase yields to a very large extent. In India, Green Revolution was responsible for our country to not only merely meet the national requirements in food production but also helped us even to export it. The green revolution was dependent to a large extent on plant breeding techniques for development of high-yielding and disease resistant varieties in wheat, rice, maize, etc.
What is Plant Breeding?
Plant breeding is the purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant.
Conventional plant breeding has been practiced for thousands of years, since the beginning of human civilization; recorded evidence of plant breeding dates back to 9,000-11,000 years ago. Many present-day crops are the result of domestication in ancient times. Today, all our major food crops are derived from domesticated varieties. Classical plant breeding involves crossing or hybridization of pure lines, followed by artificial selection to produce plants with desirable traits of higher yield, nutrition and resistance to diseases.
With advancements in genetics, molecular biology and tissue culture, plant breeding is now increasingly being carried out by using molecular genetic tools. If we were to list the traits or characters that the breeders have tried to incorporate into crop plants, the first we would list would be increased crop yield and improved quality. Increased tolerance to environmental stresses (salinity, extreme temperatures, and drought), resistance to pathogens (viruses, fungi and bacteria) and increased tolerance to insect pests would be on our list too.
Plant breeding programs are carried out in a systematic way worldwide–in government institutions and commercial companies. The main steps in breeding a new genetic variant of a crop are –
(i) Collection of variability: Genetic variability is the root of any breeding programme. In many crops, pre-existing genetic variability is available from wild relatives of the crop. Collection and preservation of all the different wild varieties, species and relatives of the cultivated species (followed by their evaluation for their characteristics) is a pre-requisite for effective exploitation of natural genes available in the populations. The entire collection (of plants/seeds) having all the diverse alleles for all genes in a given crop is called germplasm collection.
(ii) Evaluation and selection of parents: The germplasm is evaluated so as to identify plants with the desirable combination of characters. The selected plants are multiplied and used in the process of hybridisation. Pure lines are created wherever desirable and possible.
(iii) Cross-hybridization among the selected parents: The desired characters have very often to be combined from two different plants (parents), for example, high protein quality of one parent may need to be combined with disease resistance from another parent. This is possible by cross-hybridizing the two parents to produce hybrids that genetically combine the desired characters in one plant. This is a very time-consuming and tedious process since the pollen grains from the desirable plant chosen as the male parent have to be collected and placed on the stigma of the flowers selected as the female parent (In chapter 2 details on how to make crosses have been described). Also, it is not necessary that the hybrids do combine the desirable characters; usually only one in few hundred to a thousand crosses shows the desirable combination.
(iv) Selection and testing of superior recombinants: This step consists of selecting, among the progeny of the hybrids, those plants that have the desired character combination. The selection process is crucial to the success of the breeding objective and requires a careful scientific evaluation of the progeny. This step yields plants that are superior to both of the parents (very often more than one superior progeny plant may become available). These are self-pollinated for several generations till they reach a state of uniformity (homozygosity) so that the characters will not segregate in the progeny.
(v) Testing, release and commercialization of new cultivars: The newly selected lines are evaluated for their yield and other agronomic traits of quality, disease resistance, etc. This evaluation is done by growing these in the research fields and recording their performance under ideal fertilizer application, irrigation, and other crop management practices. The evaluation in research fields is followed by testing the materials in farmers’ fields, for at least three growing seasons at several locations in the country, representing all the agro-climatic zones where the crop is usually grown. The material is evaluated in comparison to the best available local crop cultivar – a check or reference cultivar.
India is mainly an agricultural country. Agriculture accounts for approximately 33 percent of India’s GDP and employs nearly 62 percent of the population. After India’s independence, one of the main challenges facing the country was that of producing enough food for the increasing population. As only limited land is fit for cultivation, India has to strive to increase yields per unit area from existing farmland. The development of several high yielding varieties of wheat and rice in the mid-1960s, as a result of various plant breeding techniques led to dramatic increase in food production in our country. This phase is often referred to as the Green Revolution.
Wheat and Rice: During the period 1960 to 2000, wheat production increased from 11 million tonnes to 75 million tonnes while rice production went up from 35 million tonnes to 89.5 million tonnes. This was due to the development of semi-dwarf varieties of wheat and rice. Nobel laureate Norman E. Borlaug, at International Centre for Wheat and Maize Improvement in Mexico, developed semi-dwarf wheat. In 1963, several varieties such as Sonalika and Kalyan Sona, which were high yielding and disease resistant, were introduced all over the wheat-growing belt of India.
Sugarcane: 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 sugar cane areas of north India.
Millets: Hybrid maize, Jowar and Bajra have been successfully developed in India. Hybrid breeding has led to the development of several high yielding varieties resistant to water stress.
Plant Breeding for Disease Resistance: A wide range of fungal, bacterial and viral pathogens, affect the yield of cultivated crop species, especially in tropical climates. Crop losses can often be significant, up to 20-30 percent, or sometimes even total. In this situation, breeding and development of cultivars resistant to disease enhance food production. This also helps reduce the dependence on the use of fungicides and bactericides. The resistance of the host plant is the ability to prevent the pathogen from causing disease and is determined by the genetic constitution of the host plant. Before breeding is undertaken, it is important to know about the causative organism and the mode of transmission. Some of the diseases caused by fungi are rusts, e.g., brown rust of wheat, the red rot of sugarcane and late blight of potato; by bacteria – black rot of crucifers; and by viruses – tobacco mosaic, turnip mosaic, etc.
Methods of breeding for disease resistance: Breeding is carried out by the conventional breeding techniques (described earlier) or by mutation breeding. The conventional method of breeding for disease resistance is that of hybridization and selection. Its steps are essentially identical to those for breeding for any other agronomic characters such as high yield.
Mutation is the process by which genetic variations are created through changes in the base sequence within genes, resulting in the creation of a new character or trait not found in the parental type. It is possible to induce mutations artificially through use of chemicals or radiations (like gamma radiations), and selecting and using the plants that have the desired character as a source in breeding – this process is called mutation breeding.
Plant Breeding for Developing Resistance to Insect Pests: Another major cause for large-scale destruction of crop plant and crop produce is insect and pest infestation. 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, e.g, 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 leaved 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. Breeding methods for insect pest resistance involve the same steps as those for any other agronomic trait such as yield or quality and are as discussed earlier. Sources of resistance genes may be cultivated varieties, germplasm collections of the crop or wild relatives.
Plant Breeding for Improved Food Quality: More than 840 million people in the world do not have adequate food to meet their daily food and nutritional requirements. A far greater number– three billion people – suffer from micronutrient, protein and vitamin deficiencies or ‘hidden hunger’ because they cannot afford to buy enough fruits, vegetables, legumes, fish and meat. Diets lacking essential micronutrients – particularly iron, vitamin A, iodine and zinc – increase the risk of disease, reduce lifespan and reduce mental abilities.
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 – (i) Protein content and quality; (ii) Oil content and quality; (iii) Vitamin content; and (iv) Micronutrient and mineral content. In 2000, maize hybrids that had twice the amount of the 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, e.g., vitamin A enriched carrots, spinach, pumpkin; vitamin C enriched bitter gourd, bathua, mustard, tomato; iron and calcium enriched spinach and bathua; and protein enriched beans – broad, lablab, French and garden peas.
Breeding of animals is an important aspect of animal husbandry. Animal breeding aims at increasing the yield of animals and improving the desirable qualities of the produce. For what kind of characters would we breed animals? Would the selection of characters differ with the choice of animals? What do we understand by the term ‘breed’? A group of animals related by descent and similar in most characters like general appearance, features, size, configuration, etc., are said to belong to a breed. Find out the names of some common breeds of cattle and poultry in the farms of your area. When breeding is between animals of the same breed it is called inbreeding, while crosses between different breeds are called outbreeding.
Inbreeding: Inbreeding refers to the mating of more closely related individuals within the same breed for 4- 6 generations. The breeding strategy is as follows – superior males and superior females of the same breed are identified and mated in pairs. The progeny obtained from such matings are evaluated and superior males and females among them are identified for further mating. A superior female, in the case of cattle, is the cow or buffalo that produces more milk per lactation. On the other hand, the superior male is a bull, which gives rise to superior progeny as compared to those of other males. Inbreeding increases homozygosity. Thus inbreeding is necessary if we want to evolve a pure line in any animal. Inbreeding exposes harmful recessive genes that are eliminated by selection. It also helps in accumulation of superior genes and elimination of less desirable genes. Therefore, this approach, where there is a selection at each step, increases the productivity of the inbred population. However, continued inbreeding, especially close inbreeding, usually reduces fertility and even productivity. This is called inbreeding depression. Whenever this becomes a problem, selected animals of the breeding population should be mated with unrelated superior animals of the same breed. This usually helps restore fertility and yield.
Out-breeding: Out-breeding is the breeding of the unrelated animals, which may be between individuals of the same breed but having no common ancestors for 4-6 generations (out-crossing) or between different breeds (cross-breeding) or different species (inter-specific hybridisation).
Out-crossing: This is the practice of mating of animals within the same breed, but having no common ancestors on either side of their pedigree up to 4-6 generations. The offspring of such a mating is known as an out-cross. It is the best breeding method for animals that are below average in productivity in milk production, the growth rate in beef cattle, etc. A single outcross often helps to overcome inbreeding depression.
Cross-breeding: In this method, superior males of one breed are mated with superior females of another breed. Cross-breeding allows the desirable qualities of two different breeds to be combined. The progeny hybrid animals may themselves be used for commercial production. Alternatively, they may be subjected to some form of inbreeding and selection to develop new stable breeds that may be superior to the existing breeds. Many new animal breeds have been developed by this approach.
Interspecific hybridisation: In this method, male and female animals of two different related species are mated. In some cases, the progeny may combine desirable features of both the parents, and may be of considerable economic value
Bee-keeping: Bee-keeping or apiculture is the maintenance of hives of honeybees for the production of honey. It has been an age-old cottage industry. Honey is a food of high nutritive value and also finds use in the indigenous systems of medicine. Honeybee also produces beeswax, which finds many uses in industry, such as in the preparation of cosmetics and polishes of various kinds. The increased demand of honey has led to large-scale beekeeping practices; it has become an established income generating industry, whether practiced on a small or on a large scale. Bee-keeping can be practiced in any area where there are sufficient bee pastures of some wild shrubs, fruit orchards and cultivated crops.
The following points are important for successful bee-keeping:
(i) Knowledge of the nature and habits of bees, (ii) Selection of a suitable location for keeping the beehives, (iii) Catching and hiving of swarms (group of bees), (iv) Management of beehives during different seasons, and (v) Handling and collection of honey and of beeswax. Bees are the pollinators of many of our crop species such as sunflower, Brassica, apple and pear. Keeping beehives in crop fields during flowering period increases pollination efficiency and improves the yield–beneficial both from the point of view of crop yield and honey yield.
Fisheries: Fishery is an industry devoted to the catching, processing or selling of fish, shellfish or other aquatic animals. A large number of our population is dependent on fish, fish products and other aquatic animals such as prawn, crab, lobster, edible oyster, etc., for food. Some of the freshwater fishes which are very common include Catla, Rohu and common carp. Some of the marine fishes that are eaten include – Hilsa, Sardines, Mackerel and Pomfrets. Find out what fishes are commonly eaten in your area.
Fisheries have an important place in Indian economy. It provides income and employment to millions of fishermen and farmers, particularly in the coastal states. For many, it is the only source of their livelihood.