- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
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'. Animal breeding is producing improved breeds of domesticated animals by improving their genotypes through selective mating.
Objectives of Animal Breeding:
The main objectives of animal breeding are: (i) Improved growth rate, (ii) increased production of milk, meat, egg, wool, etc., (iii) superior quality of milk, meat, eggs, wool, etc., (iv) improved resistance to various diseases, (v) increased productive life and (vi) increased or, at least, acceptable reproduction rate, etc.
Methods of Animal Breeding : Two methods of animals breeding are: inbreeding and outbreeding (based mainly on breeding work done with cattle).
When breeding is between animals of the same breed for 4-6 generations, it is called inbreeding. e.g. between breeds of cows, buffaloes, poultry etc.
Inbreeding may be explained by taking an example of cows and bulls.
Superior cows and superior bulls of the same breed are identified and mated.
The progeny obtained from such mating are evaluated and superior males and females are identified for further mating.
A superior female, in the case of cattle, is the cow that produces more milk per lactation.
On the other hand, a superior male is that bull which gives rise to superior progeny as compared to those of other males.
Inbreeding, as a rule, increases homozygosity.
Thus inbreeding is necessary if we want to develop a pureline 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.
But continued inbreeding reduces fertility and even productivity.
This is called inbreeding depression.
In this condition, the selected animals of the breeding population should be mated with superior animals of the same breed but those which are unrelated to the breeding population.
Outbreeding is the breeding between the unrelated animals which may be between individuals of the same breed (but not having common ancestors) or between different breeds (cross breeding) or different species (interspecific hybridization).
(i) Outcrossing. It is the mating of animals within the same breed but not having common ancestors on either side of their pedigree up to 4-6 generations. The offspring of such a cross is called an outcross. Outcrossing is the best breeding method for animals that are below average in productivity and milk production, growth rate in beef in cattle etc. Sometimes only one outcross helps to overcome inbreeding depression.
(ii) Cross-breeding. In cross-breeding, superior males of one breed are mated with superior females of another breed. Many new animal breeds have been developed by this strategy. It gives better breeds. Cows of an inferior breed may be mated to bulls of a superior breed to get better progeny. Hisardale is a new breed of sheep developed in Punjab by crossing Bikaneri ewes and Marino rams.
(iii) Interspecific Hybridisation. In this approach, male and female animals of two different species are mated. The progeny obtained from such a mating are usually different from both the parental species. But in some cases, the progeny may combine desirable characters of both the parents. Mule is produced from a cross between female horse (mare) and male donkey. Mules are sturdier than their parents and are well suited for hardwork in mountainous regions.
Controlled Breeding Experiments :
These are carried out using artificial insemination and Multiple Ovulation Embryo Transfer Technology (MOET).
1. Artificial Insemination (AI) :
The semen of superior male is collected and injected into the reproductive tract of the selected female by the breeder.
The semen can be used immediately or can be frozen for later use.
When a bull inseminates a cow naturally, approximately 5 to 10 billion sperms are deposited in the vagina.
However, when semen is deposited artificially, considerably fewer sperms are required to achieve conception.
Therefore, artificial insemination is very economical.
The spread of certain diseases can be controlled by this method.
2. Multiple Ovulation Embryo Transfer (MOET) :
In this method, hormones (with FSH-like activity) are given to the cow for inducing follicular maturation and super ovulation.
Instead of one egg, which they usually give per cycle, they produce 6-8 eggs.
The cow is either mated with a best bull or artificially inseminated.
The embryos at 8-32 cell stage are recovered and transferred to surrogate mothers.
The genetic mother is available for another super ovulation.
MOET has been done in cattle, sheep, rabbits, buffaloes, mares, etc.
High milk giving breeds of females and high quality (lean meat with less lipid) meat giving bulls have been bred successfully to obtain better breed in a short time.
Animal husbandry is the science of rearing, improvement and caring of domesticated animals.
Although the word "Animal" includes any of the various organisms belonging to the kingdom Animalia but when we use it in animal husbandry, we mean only those domesticated animals which are reared mostly for economic or for recreation purposes, such as cattle, buffalo, sheep, goat, camel, pig, horse, etc.
It also includes poultry farming and fisheries.
Since long time, animals like bees and silkworm have been used by humans.
All above mentioned livestock (animals kept for use or profit) has been used by humans for products like milk, eggs, meat, wool, silk, honey, etc.
The word 'husbandry' means the management of domestic affair.
The term used in connection with animal husbandry includes proper feeding, breeding, health care, housing etc.
Domestication of animals probably began during the 'hunting and gathering' phase of human civilisation.
As humans realised the importance of domesticating animals for use as beasts of burden and as sources of milk, meat, leather and fur, methods of improvement through selective breeding were used.
Curiosuly, Old World Agriculture employed animals.
While there is little evidence of the use of animals in the primitive agriculture of the New World.
Most of the useful animals raised today have evolved from their wild ancestors.
One of the earliest animals to be domesticated was the dog.
Starting from a few basic types, the wild dog, the wolf and the jackal, man has produced an amazing variety of breeds. The Eskimos still use huskies to draw sledges.
Cattle livestock :
Buffalo in India, termed 'water-buffalo' in the western literature, constitutes the most important species of livestock in India.
They serve as the primary source of milk -the only dietary animal protein for a majority of Indians.
The cattle are used to draw water from wells.
Their dung is used as fuel and for the generation of biogas.
India happens to be one of the largest exporters of leather goods made from cattle hide.
Horns, hooves and bones are used to prepare cattle feed and fertilizers.
Indian cattle are hardy and highly resistant to major diseases.
Bulls from India are used for crossbreeding with European and American varieties.
The best Indian cattle breeds are found in the drier parts of the country.
There are 26 breeds of cattle and seven breeds of buffaloes which differ in their body colours, horns and shape of forehead.
The family of domestic cattle is Bovidae.
There are two main groups of bovidae (domestic cattle) i.e.,
(i) Bos Indicus found in India and Africa . They are also called Zebu Cattle or humped cattle.
(ii) Bos taurus are found in Europe and North America and are non humped cattle.
The zebu is characterised by
(i) presence of prominent hump,
(ii) upright horns,
(iii) a long face,
(iv) drooping ears and
(v) large and slender legs. In the U.S. Zebus are called Brahman cattle.
The cattle breeds are classified into three groups.
(i) Milch breeds: The cows of these breeds are good milk producers, however, bullocks are of poor quality.
(ii) Draught breeds : The bullocks of these breeds are good for working but cows are poor milk producers.
(iii) General utility breeds (Dual-purpose breeds) : The cows of these breeds are good milk producers and the bullocks are good draught animals. They are intermediate between milch and draught breeds.
1. Karan Swiss: This breed has been evolved at the National Dairy Research Institute, Karnal in Haryana, by breeding the Sahiwal cows with the semen of Brown Swiss bulls imported from U.S.A.
2. Sunandini: This breed originated in Kerala by crossing the local non-descript cattle with Jersey, Brown Swiss and Holestein-Friesian breeds.
3. Karan Fries: The breed has got its origin at the National Dairy Research Institute Karnal, out of crossing between Tharparkar and Holstein-Friesian.
Some exotic (foreign) breeds of cattle (Bos taurus) that are used for cross-breeding purpose in India.
Compared to cows, buffaloes (Bubalus bubalus) generally yield more milk of high fat content.
They also have greater disease resistance and longevity.
The milk yielding capacity of buffaloes is three times more than cows. Buffalo milk is superior to cow's milk in fat content as well as minerals.
CATTLE MANAGEMENT AND FEEDING
1. India has about 227 million cattle and buffaloes. In terms of sheer numbers, India ranks fifth in the world. However, in milk production, India figures very poorly. Cattle management practices vary in different parts of the country depending upon climatic conditions. India is lowest in milk yield per cow.
Feeding: Ninety percent livestock subsists on grazing in public and government-owned lands and forests.
2. The prepared feed given to them is classified into :
(i) Roughages which include fodder, silage, hag and straw. This feed has a high fibre content.
(ii) Concentrates which include cereals, millets, forage crops with high leaf protein and oil cake, oil seeds, and animal by-products. Although low in fibre content, the concentrates have high nutrient value and digestibility. Minerals and vitamins are added to the feed of high yielders. The proportion of balanced feed differs for the young and the adult animals.
1. In the villages, a few good pedigree bulls are selected on the basis of draught ability and permitted to graze with the cows to bring about random breeding. Bulls not selected for breeding are castrated when young and converted to bullocks. They are the main source of animal draught power in India.
2. Mature cattle having more than 3 years of age should be used for breeding. The best local cows with a good milk yield should be mated with a pure breed exotic bull which should have high genetic potential. One bull is usually enough for 60 to 70 cows.
3. About 10 to 60 per cent cows are artificially inseminated by semen collected from high quality bulls. Artificial insemination ensures good quality progeny and is also economical as semen from a single bull can inseminate several thousand cows. Average gestation period of the cow is 280 days. The length of gestation of buffaloes varies, influenced by breed and environment, between 276 and 340 days, but on an average, it lasts for 310 days or 10 months, in contrast to the cow with an average gestation of 280 days or 9 months.
4. An average cow or buffalo produces 8-10 calves during its productive life time : Generally only one ovum is fertilized at a time. Selective breeding, progeny testing and improvement take longer time in the livestock than in annual food crops. With the exception of certain Indian breeds which have been maintained for good yield, the majority of Indian cattle have been on marginal inputs and are infertile and poor milk yielders. Research on the cause of infertility led to the use of pregnant mare serum gonadotropin to augment fertility in sterile cows and to induce lactation immature females by implantation of stilbesterol tablets.
5. Artificial Insemination (AI). It involves the insemination of the semen of superior bulls of exotic or indigenous breeds into the native cows. The semen should be deposited either deep in the cervix or at beginning of the body of the uterus. When insemination is performed deep in the cervix, spermatozoa are likely to live longer in the cervix than in the uterus. Deposition of semen in the vagina results in dilution, contamination and lowered conception rate. When a bull inseminates a cow naturally, approximately 5 to 10 billion spermatozoa are deposited in the vagina. However, when semen is deposited artificially into the cervix considerably fewer sperms are required to achieve conception. Therefore, artificial insemination is very economical. Semen collected from a single superior bull can be used for fertilizing many cows. Semen from desired bull located at distant places can be used. The spread of certain diseases can be controlled by this method. Artificial insemination was first introduced in India at Indian Veterinary Research Institute, Izzatnagar, Bareilly, Uttar Pradesh.
6. To increase the milk yield, Indian cows are cross-bred with European breeds like Holstein, Brown Swiss, Jersey, Red Dane and others. The Karanswiss and Sunandini are the breeds developed through cross-breeding at the National Dairy Research Institute, Karnal , and in Kerala, respectively.
7. Super Ovulation and Embryo Transplantation: It is also called as MOET (Multiple ovulation and embryo transfer) A pedigreed bull and a high production cow are chosen to produce super milch cows. Superovulation is induced by hormone injection. After artifical insemination, 4 to 10 embryos are collected at a time. Each embryo is then transplanted into a 'carrier' cow (surrogate mother). Such embryo transplants can also be carried out in sheep, goats, and other livestock. By deep freezing (-196QC), it is possible to preserve seven days old foetuses for several years to be used when needed. An embryo can be cut into two, to obtain homozygotic twins. The most beneficial outcome of embryo transplantation is the selection of high quality bulls for genetic upgrading. India has launched research using the above-mentioned techniques.
Use of Buffaloes
Milk: Buffaloes provide milk with all the essential nutrients. It has bigger size fat globules. The milk is rich in calcium and phosphorus and low in sodium and potassium. Buffalo milk is almost free from carotenoids (golden yellow in colour) due to conversion of all carotenoid materials into vitamin A (colourless by the liver cells). That is why buffalo milk and ghee is white whereas ghee made from cow milk is golden yellow in colour because of incomplete conversion of carotenoids into vitamin A inside liver cells which appears in cow milk.
Most Zebu cattle (domesticated cattle, Bos indicus) are resistant to diseases like Rinderpest or cattle plague, foot and mouth and other bacterial and viral diseases.
Rinderpest has been controlled through a National Programme.
Vaccination is given to highly productive herds.
Domesticated animals suffer from a variety of diseases.
In animals, disease may be defined as a state of discomfort associated with an abnormal function of the animals body.
Diseases may be caused by mutant genes (genetic diseases), improper nutrition or pathogens.
Genetic diseases are strictly selected against during animal breeding.
Generally, animals are raised on properly balanced diets to avoid nutritional disorders and to ensure optimum performance.
Domesticated animals suffer from diseases caused by (a) viruses, (b) bacteria, (c) protozoa, (d) fungi, and (e) animals, like worms.
Such diseases are commonly known as infectious diseases because they are caused by pathogenic infections.
Many of the infectious diseases are known as contagious diseases since they spread to healthy animals by contact with diseased animals, or with materials that were in direct contact with the diseased animals.
Some of the infectious diseases may spread to humans from the animals, e.g. anthrax.
Infections can occur through skin, digestive tract, respiratory tract, conjunctiva, urogenital tract, placenta, umbilicus, udder, teats and egg.
It is a good policy to implement measures for the prevention of infectious diseases, some of which are as follows.
(i) Isolation of animals suffering from or suspected to be infected with an infectious disease
(ii) Proper disposal of the carcass and all materials that were in contact with the diseased animals(s).
(iii) Proper cleaning and disinfection of the animal house and other materials that were in contact with diseased animal(s).
(iv) Transfer of healthy animals to a pasture other than that used by diseased animal(s).
(v) Vaccination of animals.
(vi) Injection of antiserum into healthy animals whenever an epidemic is expected.
(vii) The authorities of the veterinary department should be immediately informed of cases of infectious diseases. This will allow them to initiate measures to prevent the spread of these diseases.
Animals suffer from several bacterial diseases. For example, cattle suffer from anthrax, mastitis, pneumonia, etc.
Anthrax is caused bythe bacterium, Bacillus anthracis.
This disease is contagious and affects cattle, buffaloes, horse, sheep and goats; it can also spread to human beings.
In animals, anthrax spreads through contaminated food, water and pastures.
Symptoms and diagnosis:
In very acute cases, there is increased respiration, and blood-mixed foamy discharge from mouth, nose and anus.
In such cases, the infected animals may die within minutes.
But in subacute and chronic cases, the infected animals have high fever (up to 41.1ºC), and increased pulse and respiration rates.
There is discharge of black, shiny and foamy material from natural openings of animals.
The infected animals die within 2 to 3 days.
The anthrax bacterium uses up the oxygen carried by the animal blood.
As a result, the animals die due to a lack of oxygen.
Disease diagnosis can be confirmed by microscopic observation of the the bacterium in the blood of patients, or by culturing the bacterium present in the blood on a suitable medium.
In the case of human beings, a suitable antibiotic like ciprofloxacin is quite effective, particularly if used in the initial stages of the disease.
But in cattle, ciprofloxacin may be effective only in chronic cases.
Anthrax antiserum can also be used with good results.
In any case, antiserum should be given to all healthy animals to protect them from the disease.
Prevention and control:
The general measures for prevention of infectious diseases should be followed.
The healthy animals should be vaccinated.
Animals that have come in contact with diseased animals should be given anthrax antiserum to protect them from the disease.
2. Mastitis: It is the inflammation of udder that often occurs in dry cows due to infection of bacterium "cornybacterium pyogenes".
Animals suffer from a variety of viral diseases. For example, cattle suffer from rinderpest, foot and mouth disease, cowpox, etc. In this section, rinderpest is discussed in detail.
1. Rinderpest: This disease is caused by a virus and is highly contagious. The virus is present in all the fluids and secretions of the body of diseased animal. The disease spreads rapidly by direct contact with patient animals, through contaminated food, water, workers and their clothes and by flies.
Symptoms: Initially, the infected animal develops fever (40.0º to 42.2°C), loses appetite, develops constipation, and passes hard faeces that often are covered with blood. In the final stages of the disease, animal suffers from loose motions which gives off offensive odour. The body temperature declines and may go down below normal. The animal usually dies in about 7 days.
Treatment: Treatment is effective only when it is started in the initial stages of the disease. Injection of sulphamethazine sodium is often effective. Injection of rinderpest antiserum is highly effective, especially when combined with injection of sulphamethazine sodium.
Prevention: All the measures for prevention of infectious diseases should be implemented. It is highly desirable to vaccinate the animals against rinderpest. In 1954, a massive vaccination programme was initiated in India. This project has been highly successful, and rinderpest is no longer a dreaded disease.
Cattle of higher altitudes: Mithun is found in north-eastern India at an altitude of 700 to 1700 m. It is used for meat. Yak is found in Tibet, Ladakh, Lahaul, Spiti, Garhwal and Sikkim. Yak gives meat, hide and wool. It is also used for tilling land. The transport of people and goods across the desolate trans Himalayan region would be impossible without the yak.
2. Foot and mouth disease: If affects cattle, sheep, goats, pigs and other ruminants, caused by ssRNA Aphthovirus. It is characterised by eruption of vesicles over the lips, inside buccal cavity, over legs, feet, udder and even teats.
There is loss of appetite but dribbling of saliva is present. Lameness occurs.
The infected animals should be separated immediately and the animal house thoroughly disinfected.
3. Cow pox : It is mild self limiting eruptive skin disease of cows caused by cow pox virus. The infection is confined to udder and teats.
It spreads to humans accidently while milking infected animals.
Inoculum from cow pox lesions was used by Edward Jenner in 1798 as vaccine against small pox.
Poultry-farming deals with the rearing of fowls (chicken), ducks, turkeys, and pheasants for their eggs and meat. India and the neighbouring countries are recognised as the original home of the red jungle fowl (Gallus gallus). There is evidence that Aseel or Malay fowl were carried to Europe through the Middle East about 2,000 years ago and have given rise to the present-day European breeds.
1. Poultry and poultry products are a rich source of animal protein and other nutrients such as fats, vitamins and minerals. Consumption of eggs would pave the way for overcoming protein malnutrition prevalent especially among children in India.
2. Poultry-farming has definite advantages over livestock-rearing. Poultry birds are easy to raise, can be acclimatised to a wide range of climatic conditions, have short life span and are prolific breeders. Hens have an average yield of 60 eggs per year (upto 240 eggs in high-yielding varieties). Poultry-farming requires less space, is easier to manage and maintain and brings fast returns within a span of six months.
3. In a poultry farm, comfortable, well-ventilated and illuminated dry houses are built. Birds of different ages are kept in separate houses. In regions with moderate climate, they are kept in cages (coops). The floor is littered with chopped straw, paddy husk, dry leaves or ground nut hulls. It is made rat proof and provided with water channels with proper drainage. Minerals which are important for poultry diets are calcium, phosphorous, sodium, copper, iodine, iron, manganese and zinc. Vitamins required are vitamin A, 0 3' E, pyridoxine, riboflavin, pantothenic acid, niacin, folic acid, B12 and choline. The male breeder's diet should contain extra calcium, manganese and vitamin E to ensure proper fertility. Thus, a balanced diet is the requirement so that the utilization for building of tissues and egg production is maximised. Clean and fresh water is very essential for birds.
Light management: Light is essential for high egg production. 14 to 16 hours of light including daylight is required for optimum production. When the pullets (young hens especially at the time they begin to lay eggs) come into production, start giving additional light if the daylight is less than 12 hours. Gradually increase the light 20 minutes every week till 16 hours of total light is there. One tube light of 40 watt is sufficient for 36 sq.m area while 40 watt bulb is sufficient for 18 sq.m floor area. Light should spread uniformly. The light should not be provided for whole night.
4. Fowls are widely distributed as domestic animals and the most common species of jungle fowls are Gallus gallus, G. lafayetti and G. sonneratti.
5. Poultry feed includes all the nutrients and is made of cereals and millets, oil cake, protein concentrates, fish and meat meal, minerals and green vegetables.
6. The domestic fowl (Gallus domesticus) population of our country can be roughly classified into two types:
(i) Indigenous (desi type), (ii) Exotic (improved type)
Some of the indigenous breeds like Aseel , Karaknath, Ghagus, Brahma, Busra are the best table birds. The Aseel fowls are used in cock-fighting. The exotic breeds are classified, according to their source of origin, into American class, English class, Mediterranean class and Asiatic class. Some examples are White Leghorn, Rhode Island Red, Plymouth Rock and New Hampshire. They are now completely acclimatised to Indian conditions. Some of them are excellent egg-layers, whereas others give good meat.
Table : Breeds of Chickens
The indigenous breeds are crossed with exotic breeds for improving egg production. Heterosis has been utilised for producing better egg layers and broilers (birds grown for meat) with high nutritive value.
Some of the diseases like fowl pox, ranikhet, coryza, fowl cholera and aspergillosis take a heavy toll on poultry. But with better management, proper housing and nutrition and timely vaccination of the chicks, these diseases can be controlled.
7. Ducks comprise 6 per cent of the total poultry population in India. They are abundant in the southern and eastern parts of India. There are 20 breeds of duck of which Muscori, Pekin, Aylesbury and Campbell are popular exotic breeds; indigenous breeds include Indian Runner, Syhelt meta, etc. Brown and white geese are common in India. Turkeys which are in demand during Christmas time, belong to the breeds Narfold, British White, Broad Breasted Bronze and Beltsville Small White.
8. Poultry Diseases
(i) Encephalomalacia: Deficiency of vitamin E causes softening of brain tissue in young poultry.
(ii) Coccidiosis: The protozoan Eimeria causes coccidiosis in fowls. It causes bloody diarrhoea.
(iii) Bacterial Diseases
Viral Diseases: Ranikhet, Fowl pox, Infectious bronchitis, Lymphoid leukosis.
Fungal Dieases: Thrush, Aflatoxicosis, Brooder pneumonia.
Ranikhet Disease is respiratory disease caused by Paramyxovirus characterised by coughing, sneezing and marked signs of respiratory diseases. Also known as 'New Castle disease'.
Marck's disease is primarilya disease of the young growing fowls caused by DNA virus. Paralysis is one of the major clinical symptoms.'
Bird Flu resembles influenza and is caused by a virus HN1. The virus enters the man through chicken.
Coccidiosis caused by a group of protozoans called coccidia (e.g. Eimeria, Isopora) which affect the different parts of intestine.
Tick fever is transmitted through the fowl tick (Argus persicus). Usually tick bites the birds at night and parasite is transmitted into blood. High temperature, dullness, depression, greenish diarrhoea are its symptoms.
Perosis is due to deficiency of manganese in poultry birds. There is enlargement of tibiometatarsal joint twisting and bending of end of tibia.
Infectious Coryza is caused by Haemophilus gallinarum and infected birds show discharge from the nostrils and eyes.
Pullorum disease is caused by Salmonella pullorum. The heart, spleen, liver, kidney, lung and digestive tract are affected.
Aspergillosis is mainly disease of young chick and is caused by a fungus Aspergillus fumigatus. Normally the lungs are the major area of internal infection.
Mycosis is caused by a yeast called Candida albicans. It affects mostly upper portion of the digestive tract (mainly crop, proventriculus and gizzard).
It is the care and management of honey bees. Honey bees give us honey and wax. They are good pollinators.
1. Common breeds of honey bee are
Apis dorsata (Rock bee)
Apis indica (Indian bee)
Apis florea (Little bee)
Apis mellifera (Italian bee)
2. Honey produced by the honey bee Apis species is probably the oldest sweetening agent in our civilisation. Honey contains two sugars -dextrose and levulose -and a mixture of several other substances. It is tasty, health-giving and also medicinally useful. Honey bees also yield wax, which has multiple uses. A large quantity of honey is still collected from wild sources. However, bee-keeping (apiculture) using domesticated bees has been practised in many parts of the world, including India (using A. dorsata, A. florea and A. indica).
3. Social organization (Castes) of honey bee: The nest of honey bee is known as the bee-hive. The hive consists of 32 to 60 thousand individuals, showing a highly organized division of labour in the colony. Bees are polymorphic, consisting of three types of individuals (Castes) viz, QUEEN, DRONE and WORKER. The characters are given in the following table.
4. From its mandibular gland, the developing queen secretes antiqueen substances or antiqueen pheromones which inhibit the worker bees from building brood chambers and developing ovaries.
5. Drones are male honey bees. They develop from unfertilized eggs. The phenomenon is called arrhenotoky. Drones and virgin queens take part in nuptial flight. After copulation, the drones are not allowed to come back into hive.
6. The queen stores the sperm in her spermatheca. They are sufficient to fertilize all the eggs that are laid by her.
7. Females develop from fertilized eggs. Workers are sterile females. Scout bees search for food and intimate the same, to worker bees by dances -round dance for less than 75 m and tail wagging dance for longer distances (Frisch) of the new food source from the hire.
8. Workers have a pollen collecting apparatus in hind legs called corbicula and nectar storing mechanism in crop and wax secreting glands in abdomen.
9. Young workers secrete royal jelly and are called nurse bees. Royal jelly is given to queen or potential queens. Apiculture is the rearing of bees or bee keeping for collecting of honey and wax.
10. Honey is near neutral sugary syrup with 6.8 pH, having 17-25% water, 3.3% minerals, abundant vitamins (B1, B6, C, D), L-fructose (Laevulose, 41%), glucose (35%), sucrose (1.9%) and dextrin (1.5%). It is tonic, laxative and sweetening agent. Bee wax is secreted by abdominal wax glands of the worker bees. It possesses a hardening substance from cephalic gland and a resin called propolis from pollen grains.
Importance of Honey bees: Honey bees have the following importance.
1. Honey: The honey is a natural valuable tonic for human body. It contains various substances of high medicinal value, including important enzymes, vitamins and sugars, mainly glucose and fructose. It prevents infection if applied to a wound. A number of ayurvedic medicines are taken with honey.
2. Bee wax : Bee wax is made of secretion of worker bees' abdominal glands. It is a product of industrial importance. It is used in the manufacture of many items including cosmetics, shaving cream, face cream, ointments, plasters, carbon papers, pencils, electric goods, toothpaste, lotions, furniture-polishes, boot-polishes, protective coating, ink paints and candles. It is also used in model and mould making and in printing industry. It is also used in the laboratory for microtomy with the common wax for block preparation of the tissues.
3. Pollination: The honey bees are pollinators of many crop species such a sunflower, Brassica, apple and pear.
4. Medicinal value: A drug, prepared from the bodies of honey bees, is used in the treatment of Diphtheria and some other dangerous diseases. The venom of honey bees has been used in the treatment of arthritis and snake bite.
The detailed studies on the habits and behaviour of the honey bee led to the development of apiculture not only as a useful hobby but a large scale profitable trade to produce honey and wax in large quantities.
The honey-bees are reared in wooden boxes having a large brood chamber placed on a wooden platform with an opening for the entry and the exit to the bees at the bottom.
A number of frames coated with wax sheets having hexagonal imprints are placed in the chamber vertically with the help of wires.
The bees start making cells along the margins of hexagonal imprints.
Each wax sheet, known as comb foundation, provides the foundation arc for the bees to build combs on both the sides.
Another frame fitted with wire meshing for the easy passage of the workers is placed over the vertically placed frames.
A chamber called super having additional similar frames for more comb foundations meant for the expansion of the hive, is placed over the brood chamber.
The wire meshing referred to above, extends between the brood chamber and super.
In order to provide ventilation, light and protection, a cover having holes is placed over the super.
To start a colony in the artificial hive, a gravid (fertilized) queen is inducted into the brood chamber.
Artificial hives are placed in gardens, orchards and fields having flowering plants to provide the pollen and nectar.
When sufficient honey has been stored, the combs are removed from the frames and then centrifuged to extract the honey.
The same comb can be used again.
The appliance used for the extraction of honey are a pair of gloves, a knife, a brush to remove the bees from taken out combs and a centrifuge.
Bee Enemies: These include the wax moths (e.g., Galleria mellonella), wasp (e.g., Vespa) , black ants (e.g., Componotus compressue) and bee eaters (e.g., Merops orientalis and king crow, Dicrurus macrocerus). Man is the last but worst enemy of honey bees.
Bee Diseases : Honey bees suffer from Nosema disease caused by a sporozoan Nosema apis, paralysis dysentery and acarine disease caused by a parasitic mite, Acarapis woodi.
A large section of the Indian population uses fish as food. Fish is an easily available source of protein. It is highly nutritious and easily digestible. In India, edible fishes are abundantly available from sea, rivers, lakes, ponds and marshes. Fish is also an item of export trade.
"Aquaculture" involves production of useful aquatic plants and animals such as fishes, prawns, shrimps, lobsters, crabs, molluscs (edible and pearl oysters) by the proper utilisation of small and large bodies of water. "Pisciculture" is the production of fishes.
Fishes are reared in small rivers, lakes and canals.
Fish eggs are introduced into nurseries (hatcheries).
The young ones hatched from the eggs are fed, tended and nursed and harvested when full grown.
Aquaculture techniques of induced breeding by the administration of pituitary hormones have helped in the production of seed fish in pure form.
Hatcheries with Circulating water have ensured almost 100 percent hatching of fertilised eggs.
Culturing fish in fresh water is known as 'Inland fisheries'.
Fish industry also includes trapping and capturing fishes from estuaries, sea coast and even from within the sea by using sophisticated electronic locaters, baits, nets and trawlers.
A large number of fishermen living in the coastal regions of India still use catamarans and various traditionally built boats.
Mechanised fishing boats have now made deep-sea fishing possible.
Catching, processing and packaging of marine fishes have been developed on a scientific footing in our country.
India exports marine food to several countries.
Besides serving as table food, fishes are of medicinal value.
Shark liver oil and cod liver oil are natural sources of vitamins A, C and D.
Oil from sardines, herrings and salmon is used in the manufacture of soaps and paints.
Fish meal is a rich source of protein for cattle and poultry. It is prepared from the nonedible parts of fishes such as tails, fins and bones which are discarded from factories that extract oil from fishes. Fish waste is also used for making fertilisers and adhesives. Shark leather (shark skin) called shagreen is used to make articles such as hand bags, shoes and tobacco pouches and is considered fashionable and fetches a high price in the market.
Pisciculture is rearing, catching and management of fishes.
Culture fishery is the raising of fishes in tanks and ponds while capture fishery is management of catching of fish without actually raising them.
India has 1.6 million hectares of inland water (annual yield 2.242 million tonnes, 1996 data) and over 2.59 km2 of continental shelf for fishing (annual yield 2.7 million tonnes, 1996 data).
Table : Important Edible Fishes of India
Culture Fishery: In this method, pituitary hormone extract is injected into male and female breeder fish.
Two males and one female are then kept in a breeding happa, a bamboo and cloth container.
Spawning takes place in 3-6 hours.
The fertilized eggs are removed and kept in hatchery, where they hatch in 15-18 hours.
The hatchlings are kept in glass-jar hatcheries.
A mouth is formed on the third day and the young fish are now called fry.
They are kept in rearing ponds for about three months, where they grow into 4"-6" long fingerlings.
The fingerlings are then released into stocking ponds where they grow to the required size.
In composite fish culture, different species of fish like catla, rohu and mrigal are cultured together.
Types of Ponds: Three types of ponds are required for the culture of Indian major carps: nursery, rearing and stocking ponds.
(i) Nursery Ponds: Efficient pond fish culture requires special preparation of nurseries to receive the tender hatchlings at spawn. Small and seasonal nurseries are preferred as they facilitate effective control of the environmental conditions. The steps adopted towards preparation of nurseries are control of predatory fishes and weeds, There should be production of zooplankton to serve as food for spawn and control of algal blooms.
(ii) Rearing Ponds: The fries (sing. fry = young one of fish) are collected from the nursery ponds and released in rearing ponds where fries develop into fingerlings.
(iii) Stocking Ponds: The fingerlings are netted out from the rearing ponds to stocking ponds where they change to fish. In the stocking ponds, the fishes are kept for stocking.
Marine fisheries: The marine fishery is divided into coastal fisheries (about 3 miles from the coast line), and deep sea fisheries, which have different fauna of fish. In India, about 75% of the marine fish catch is from the western coast.
The main marine fisheries are Sardines (26%), Mackerel (9.7%) and the Bombay duck (11%).
Crustacean fisheries i.e. Prawns, Lobsters, Crabs, Penaeus sp. are dominant on the west coast. Mollusc fisheries include oysters, clams, mussels, squids, cuttlefish and octopus.
Estuarine fisheries : The place where the fresh water of rivers meets the salt water of the sea is called an estuary. It contains brackish water.
At estuary only those fishes of fresh water and sea can survive that can tolerate a change of salinity.
The estuary also forms the nursery ground for several marine and fresh water species.
Fishing on large scale from such places, results in the death of number of young and immature fishes.
Bag nets are most commonly used in estuarine fishery.
The major estuarine systems in India are (1) Hooghly -in West Bengal. (2) Mahanadi estuary in Orissa. (3) Cauvery estuary in Tamil Nadu. (4) Narmada and Tapti estuary in Gujarat and (5) Godavari-Krishna estuary in Andhra Pradesh.
Carp fishes such as catla (theila), Labeo rohita (rohu), Cirrhinus mrigala (mrigal) and Labeo calbasu (kalbasu) are commonly cultured together in our country.
Such a practice of culturing together of fishes is called polyculture or composite culture.
Important edible fishes are :
A. Fresh water fishes: Rohu (Labeo rohita), Calbasu (Labeo calbasu), Catla (Catla catla), Singhara (Mystus singhala), Magur (Clarias batrachus), Singhi (Heteropneustes)
B. Marine fishes : Bombay duck (Harpodon sp.), Hilsa (Hilsa sp.), Eel (Anguilla sp.), Pomphret (Stromatetis sp.), Salmon (Aluitheronema sp.), Sardine (Sardinella sp.)
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
MAIN STEPS IN PLANT BREEDING
The main steps in breeding a new genetic variety of a crop are the following:
Collection of Variability :
Genetic variability is the root of any breeding programme.
In many crops preexisting genetic variability is available from wild relatives of the crop.
Germplasm is collected from within country (IC – Indigenous collection) and also from other countries (EC – Exotic collection).
The germplasm collections are usually maintained at low temperature in form of propagules.
The stored propagules are periodically grown in the field to obtain fresh propagules.
In fruit trees, the germplasm is maintained as trees grown in the field.
Collection and preservation of all the different wild varieties, species and relatives of the cultivated species is a pre-requisite for effective exploitation of natural genes available in the population.
Germplasm is the sum total of all the alleles for all the genes present in a crop and its related species.
The entire collection (of plants/seeds) having all the diverse alleles for all genes in a given crop is called germplasm collection. A good germplasm collection is essential for a successful breeding programme.
Therefore, germplasm collection is the most practical and effective answer to problem like loss of germplasm due to expansion of agriculture, industries and other human activities.
Evaluation and Selection of Parents :
The germplasm is evaluated to identify plants with desirable combination of characters.
Selection of parents is done by picking up seeds of only those plants for multiplication which have the desired traits.
Selected plants are multiplied and used in the process of hybridisation. Pure lines are created wherever desirable and possible.
Common Methods of Crop Improvement
(a) Selection :
Selection is the oldest method of crop improvement.
Almost all our present day crops are the result of selections carried out by prehistoric human beings.
During selection, the individual plants or groups of plants having desired characters are picked up from population, eliminating the undesirable ones.
The selected parents are allowed to reproduce for setting their seeds. The seeds are collected and again a new crop is developed. Selection is again done in this new crop.
It is of three types:
(i) Mass selection :
Simplest and oldest method mainly for cross pollinated crops and is based on phenotypic characters.
It is most common method of crop improvement.
In this, large number of plants of a species with similar phenotypic characters are selected and their seeds are mixed together at time of harvesting.
These seeds are sown in field for progeny testing. Progeny selection is done by eliminating the undesirable one and saving the best.
(ii) Pure line / Inbreed selection :
Involves isolation of desirable homozygous individuals and is done for self pollinating crops.
A pure line is the progeny of a single homozygous self pollinated plant. In this method, a plant with desired characters is selected from a genetically mixed population.
The single selected plant is self pollinated during subsequent generations to pick out a true breeding species with desired characters.
Once homozygosity is confirmed, the individual is multiplied on a large scale and recommended to farmers. e.g., Wheat varieties like : PV - 18; HUW - 468, Kalyan Sona
(iii) Clonal selection :
It is used for vegetatively reproducing crops. Progeny of a single vegetatively propagated plant is called clone. Here selection is made between clones and not within clone e.g., Kufri safed potato.
(b) Hybridisation :
Hybridisation is the process of making a cross between two genetically diverse parents to obtain a progeny with desired superior traits.
The desired characters very often combines from different parents. For example high protein quality of one parent may need to be combined with disease resistance from another parent.
When a hybridisation is performed between two plants it is called single cross and when it is performed between more than two plants, it is called multiple cross e.g., development of C-306 wheat variety and IR-36 rice variety.
It is not necessary that the hybrids do combine the desirable characters, only one in few hundred to a thousand crosses shows the desirable combination. The primary aim of hybridization is to produce variations.
First natural hybridisation was reported in corn (Maize). First artificial hybrid was obtained by crossing sweet william and carnation by Thomas Fair child and is known as fairchild mule.
Hybridisation was first practically utilised in crop improvement by Kolreuter.
(c) Mutation Breeding :
Mutation is sudden, stable and inheritable change which alter the gene expression of organism. This results in a new character not found among parents.
The mutations, which are artificially induced by treatment with certain physical or chemical agent are called induced mutations.
The application of induced mutations for crop improvement is called mutation breeding.
The agents which are used to induce mutations are called mutagens.
Various chemicals such as HNO2 base analogues, alkylating agents, acridine dyes, and physical agents such as X-rays, UV-rays and gamma rays are used to induce mutations which produce desirable qualities.
It has been used commonly in self pollinating crops.
A number of new varieties have been developed e.g.,
(i) Sharbati Sonora and Pusa Lerma varieties of wheat (formed basis of green revolution in India).
(ii) Reimei, Atomita-2 and Jagannath varieties of rice.
(iii) Erectiferum and Erectoids varieties of barley.
(iv) Aruna variety of castor.
(v) Thick shell in ground nut (TGI)
(vi) Wheat - NP 836
(vii) Cotton - lndore-2
(viii) In mung bean, resistance to yellow mosaic virus and powdery mildew.
(ix) Peppermint (Mentha piperita) - Todd's Mitcham variety, (high oil content and disease resistant).
(d) Polyploid Breeding :
Organisms having more than two sets of chromosomes are called polyploid.
Induced polyploidy is used by plant breeders for improving yield of forage and other crops.
Many of modern day crops such as wheat, rice, sugarcane, potato and cotton are natural polyploids.
The allopolyploids have been used for obtaining fertile hybrids between different species and genera.
Allopolyploidy immediately forms new species.
Odd-numbered polyploids (3x, 5x etc.) are usually sterile, while even-numbered polyploids are fertile.
Allopolyploids are produced in two steps, as follows - First of all, two different species are hybridised to produce F1. The F1 is usually sterile.
Therefore, in the second step, the chromosome number of the F1 is doubled.
The resulting allopolyploid is usually, at least, partially fertile and forms a new species.
Many alloployploids have been produced in nature, some of which have succeeded as crops e.g., wheat.
Humans have produced a new alloployploid crop called Triticale in the following manner.
Allotetraploid wheat (Triticum turgidum) was hybridised with rye (Secale cereale; a diploid grass).
The chromosome number of the resulting F1 was doubled to produce Triticale. Triticale is cultivated in some areas of Punjab and in the hilly regions of the country.
Selection and Testing of Superior Recombinations :
This step comprises of selecting, among the progeny of the hybrids, i.e. those plants that have the desired character combination.
This is the crucial step for the success of breeding experiment, so require careful scientific evaluation of progeny.
The selection process yields plants that are superior to both of the parents.
These plants are self-pollinated for several generations till they come to a state of uniformity (hornozygosity) so that the characters will not separate in the progeny.
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 field and recording their performance under ideal fertilizer, irrigation etc.
The testing of the materials is done in the farmer's fields, for at least three growing seasons at different locations in the country, representing all the agroclimatic zones.
The material is evaluated in comparison to the best available local crop cultivar - a check or reference cultivar.
Finally the seeds of desirable plants are certified by National Seed Corporation (NSC) for marketing.
India is an agricultural country. Agriculture contributes about 33% of India's GDP and gives employment of about 62% of the population.
The development of several high yielding varieties of wheat and rice in mid 1960's increased the yield per unit area. This phase is often referred to as the Green Revolution.
From 1960 to 2000 wheat production increased from 11 million tonnes to 75 million tonnes while rice production increased from 35 million tonnes to 89.5 million tonnes.
This was due to the development of semi-dwarf varieties of wheat and rice.
A dwarfing gene Norin-10 was reported in Japan.
American plant breeders produced single dwarf wheat. N. Borlaug developed triple dwarf wheats in Mexico, popularly known as Mexican Wheats.
These had high yield, resistance for lodging, common pathogens and pests, photoinsensitive, fertilizer responsive and have smaller growth period.
Sonora-64 and Lerma Rojo-64 were brought to India and modified through gamma mutations so that these can become part of Indian Agriculture.
In 1963, many varieties like Sonalika and Kalyan sona were introduced in all wheat growing belts of India.
A dwarfing gene dee-geo-woo-gen, was reported in Taiwan.
It was introduced in rice varieties by IRRI, Philippines in varieties IR-8, IR-24.
Taichung Native-1 was developed in Taiwan. Later better yielding semi dwarf varieties Jaya and Ratna were developed in India.
Saccharum barberi was originally grown in North India, but had poor sugar content and yield.
Tropical canes grown in South India i.e. Saccharum officinarum had higher sugar content and thicker stems but did not grow well in North India.
These two species were crossed to get sugarcane varieties combining the desirable qualities of high sugar, high yield, thick stem and ability to grow in the sugarcane belt of North India.
Hybrid bajara, jowar and maize have been developed in India. From hybrid varieties, the development of several high yielding varieties resistant to water stress were taken over.
PLANT BREEDING FOR DISEASE RESISTANCE
Fungal, bacterial, viral and nematode pathogens attack the cultivated crops. So crop loss can be upto 20-30 percent, sometimes even total.
In such situation if the crops are made disease resistant, food production is increased and use of fungicides and bacteriocides would be reduced.
(1) The development of diseases in a plant depends on the interactions among following factors :
(a) Host genotype
(b) Pathogen genotype
(c) The environment
(2) Some host genotypes possess the ability to prevent a pathogen strain from producing disease. Such host lines are called resistant, and this ability is called resistance.
(3) The term strain has a similar meaning for the pathogen as line has for the host, Those lines of a host that are not resistant to the pathogen are called susceptible. A successful breeding for disease resistance depends mainly on the following two factors :
(a) A good source of resistance
(b) A dependable disease test. In disease test, all the plants are grown under conditions in which a susceptible plant is expected to develop disease.
Some Important Diseases of Economically Important Plants (A Brief Information)
(a) Late Blight of Potato :
The disease is famous as it caused Ireland famine of 1845.
The disease occurs in all potato growing areas of the world. It is most destructive under cool and moist conditions.
The pathogen is Phytophthora infestans. The disease kills the foliage of crop because of which the yield is reduced.
The disease not only infects potato tubers in the field, but also continues to advance inside the tubers under storage conditions.
Symptoms : They appear first as water soaked or hydrotic areas along the margin and tips of lower leaflets. The spots enlarge rapidly, become necrotic, turn brown and then blackish or blighted. The infected leaves become limp, appear blighted and rot away, producing a characteristic odour.
(i) Seed tubers should be free from infection.
(ii) Disease Resistant varieties.
(iii) Fungicides. In susceptible environment and disease prone areas, the crop should be sprayed or dusted with fungicides.
(b) Loose Smut of Wheat
Causal organism : Ustilago nuda tritici.
Symptoms : It is recognized as soon as the effected inflorescence emerges from leaf sheaths. In the smutted deformed inflorescence, spikelets are completely filled with black, dry, powdery mass of chlamydospores (brand spores), the skin of fruit wall bursts, soon exposing the spores
Control measures : Disease resistant varieties and fungicides. In susceptible environment and disease prone areas, the crop should be sprayed or dusted with fungicides.
(c) Black Rust of Wheat
Causal organism : Puccinia graminis tritici.
Symptoms : Black rust or stem rust of wheat is seen on the stem and leaf sheaths. Both uredosori and teleutosori are seen. Uredospores are brownish, spherical or oblong and teleutospores are black and elongated. As this rust is heteroecious, uredosori and teleutosori are found on Wheat, whereas some other stages are found on other host, Barberry.
Control measures : Disease resistant varieties, fungicides. In susceptible environment and disease prone areas, the crop should be sprayed or dusted with fungicides.
(d) Bacterial Blight of Rice :
It is caused by bacterium Xanthomonas oryzae.
The infected tissues collapses and are digested by bacteria. Lesions enlarge and become necrotic.
The stems and the leaves of infected plant give blighted or burnt up appearance.
Control measures include rogueing, 3-year crop rotation, spray of agrimycin plus copper oxy-chloride and antibiotics besides sowing disease resistant varieties.
(e) Cucumber Mosaic Disease / Beans Mosaic Disease
It is world-wide disease caused by an isometric single stranded RNA virus called Cucumovirus having fragmented genome.
The virus seems to have the widest range of hosts, attacking different types of plants like cucumbers, melons, squash, gladioli, crucifers, banana, celery, spinach, pepper, beans, chickpea (gram) etc.
It attacks plants which are 5-6 weeks old. Infected plants develop bunched or bushy appearance.
There is mottling, distortion, wrinkling, curling and dwarfing of leaves. Later on leaves fall down. Flowers and fruits also develop distortions.
It is transmitted by a variety of methods including aphids, agricultural implements, farm workers, air, water and other mechanical means.
Control measure : Disease resistant varieties.
(f) Root Knot of Tomato and Brinjal
The disease is quite common in all vegetable growing areas especially where the climate is warm with short or mild winters.
It devitalizes root tips, develop swelling over roots and reduces flow of water and minerals to the aerial parts.
As a result, yield and quality of fruits are affected. The disease is caused by root knot nematode Meloidegyne incognita.
Symptoms : The main as well as lateral roots develop a number of spherical to elliptical swellings or galls. The diameter is 2 to several times the diameter of the root. They include reduced growth, smaller, fewer yellow leaves which tend to wilt. Flowering is reduced. Fruits are fewer and of poor quality.
(i) Biological control. Nematode infested soil is inoculated with spores of bacterium Pesteuria penetrans, fungus Dactylella oviparasitica and VAM fungus.
(ii) Resistant varieties. It is always preferred to grow varieties resistant to root knot nematodes.
(iii) Flooding of the fields eliminates the root knot nematodes.
(iv) Steam sterilization and fumigation with nematicides free the soil of nematodes.
Methods of Breeding for Disease Resistance
Breeding is carried out either by conventional breeding techniques described earlier or by mutation breeding.
The conventional method of breeding for disease resistance is hybridisation and selection.
Conventional breeding is often constrained by availability of limited number of resistance genes identified in crop.
The various steps are:
(1) Screening germplasm for resistance sources
Wild plants can be a best source because they survive without getting protection from humans in any environment. Their characters are useful for plants breeders; for example potato has got
(i) Resistance to potato virus X and potato leaf roll virus from Solanum acaule.
(ii) Resistance to five races of cyst nematodes and to fungus Fusarium coeruleum from Solanum spegazzini.
(iii) Resistance to potato virus from Solanum stoloniferum.
(iv) Resistance to Phytophthora infestans from S. demissum.
(v) Resistance to red rot of sugarcane and adverse environment in noble sugarcane (Saccharum officinarum) was conferred from the wild Saccharum spontaneum.
(2) Hybridization of selected parents
(3) Selection and evaluation of hybrids
(4) Testing and release of new varieties.
Some released crop varieties bred by hybridisation and selectionfor disease resistance to fungi, bacteria and viral diseases
New varieties having these desirable characters can either be multiplied directly or can be used in breeding.
Constraints of conventional breeding like the limited availability of limited number of disease resistance genes can be overcome by this method.
Other useful breeding methods like mutation, selection among somaclonal variants and genetic engineering.
In mung bean resistance to YMV and powdery mildew were induced by mutations.
Resistance to YMV in bhindi (Abelmoschus esculentus) was transferred from a wild species and resulted in a new variety of A. esculentus called Prabhani Kranti.
Plant Breeding for Developing Resistance to Insects / Pests
Insects and pest infection is another major cause for large destruction of crop plant and crop produce. Insect resistance in host crop plants is due to morphological, biochemical or physiological characters.
Solid stem in wheat lead to non-preference by the stem saw fly.
Smooth leaved and nectar-less cotton varieties do not attract bollworms. Low nitrogen, sugar and high aspartic acid in maize develops resistance to maize stem borers.
Some released crop varieties bred by hybridisation and selection for insect pest resistance
Sources of resistance genes may be cultivated varieties, germplasm collections of the crop or wild relatives of the crop.
Plant Breeding for Improved Food Quality
It is estimated that more than 840 million people in the world do not have adequate food to meet their daily requirements.
Three billion people are suffering from 'hidden hunger' as their diet shows deficiencies in proteins, vitamins and micronutrient because these people cannot afford to buy adequate vegetables, fruits, legumes, fish and meat.
Breeding of crops with higher levels of vitamins and minerals or higher protein and healthier fats is called biofortification.
Plant breeding is undertaken for improved nutritional quality of the plants, with the objectives of improving:
(i) Protein content and quality
(ii) Oil content and quality
(iii) Vitamin content
(iv) Micronutrient and mineral content
Cereals are commonly deficient in lysine and tryptophan, while legumes are commonly deficient in sulphur containing amino acids like methionine and cysteine.
In 2000, maize hybrids that had twice the amount of lysine and tryptophan were developed as compared to existing varieties.
Three lysine rich maize varieties have been developed in India are Protina, Shakti and Rattan.
Wheat variety Atlas 66 with high protein content has been used as a donor for improving cultivated wheat.
Indian Agricultural Research Institute (IARI), New Delhi, has also developed many vegetable crops that are rich in minerals and vitamins.
For example, vitamin A enriched carrots, pumpkin, spinach, vitamin C enriched bitter gourd, bathua, tomato, mustard, calcium and iron enriched spinach, bathua and protein enriched beans (broad lablab, french and garden peas).
Breeding for Anti-nutritional Factors
Nutritional quality of a crop generally means improvement in its produce which can be suitable for human (animal nutrition).
Anti-nutritional factors are compounds present in foods and have adverse effect on animal and human growth.
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
SINGLE CELL PROTEIN (SCP)
Some microorganisms like bacteria, blue green algae, yeasts and filamentous algae are used as food and are called SCP.
They are processed to remove excess nucleic acid.
The raw materials for single cell protein production include whey, sulphite waste liquours, hydrocarbon waste from petroleum industry, waste water containing starch from potato processing plants, straw, molasses and animal manure.
The microorganisms are grown in large fermenting tanks with forced aeration for vigorous cell growth. Microorganisms which can be explored for obtaining SCP are:
(i) Algae : Spirulina, Scenedesmus, Chlorella
(ii) Fungi : Fusarium graminearum, Candida utilis, Trichoderma viride
(iii) Bacteria : Achromobacter, Cellulomonas, Methylophilus methylotrophus (Source of Pruteen) : 250 g of this microorganism can be expected to produce 25 tonnes of protein per day.
It is a manure prepared from young, green crop plants by ploughing them back into soil.
Usually, young leguminous crops are used for green manuring because they also increase the nitrogen fertility of the soil.
The plants commonly used for green manuring in India are : Sunn Hemp (Crotolaria juncea), Dhaincha (Sesbania aculeata), Cluster Bean (Cyamopsis tetragonoloba), Sweet Clover (Melilotus parviflora), Cowpea (Vigna sinensis), Horse Gram (Dolichos uniflorus), Egyptian clover (Berseem, Trifolium alexandrinum), Lentil (Lens esculenta).
The plants are rich in nitrogenous compounds because of the presence of nodules on the roots. Sesbania rostrata possesses such nodules on the stem (caulinary nodules) as well.
The plants are slowly converted into manure through the activity of microorganisms. Green manures have all the benefits of farmyard manure.
Additionally, they increase nitrogenous content of the soil, reduce alkalinity and prevent soil erosion.
It is found that green manures increases crop yield by 30-50% as compared to farmyard manure.
In the face of rising prices and shortage of fossil fuel, attempts are being made to use alcohol for running automobiles.
Both ethanol (ethyl alcohol) and methanol (methyl alcohol) can be used for this purpose.
Proalcohol programme of Brazil envisages the complete replacement of petrol or gasoline with alcohol.
Gasohol programme of U.S.A. contemplates 10-15% blend of alcohol with petrol. While Brazil is concentrating on preparing alcohol from Sugarcane, U.S.A. is experimenting with Maize.
Besides Sugarcane and Maize, other crops which can be used for production of alcohol are Potato, Sugar beet, Tapioca and molasses of sugar industry.
Growing crops for production of alcohol and other fuels is known as energy cropping.
The existing gasoline engines require only little modification for using gasohol or pure alcohol.
One problem with employing alcohol as fuel is the cost of production. Another problem is the reduction in agricultural land.
This will reduce the amount of food available for feeding human population.
Nobel Laureate, Melvin Calvin, suggested that the shortage of petrol can be overcome by extracting them from certain plants popularly called petroleum plants.
The plants produce a large amount of latex. Latex contain long chained liquid hydrocarbons.
These long chained hydrocarbons can be used directly or broken to hydrocarbons of chain length similar to the ones present in petrol.
Petroleum plants belong to families Euphorbiaceae, Asclepiadaceae, Apocyanaceae and Asteraceae.
The two plants investigated for petroleum products are Euphorbia lathyrus (family Euphorbiaceae) and Brickellia species (family Asteraceae).
Other useful plants are - Jatropha curcas and Pongamia pinnata. Limitation : Commercial exploitation of petroleum plants seems to be not yet feasible because the product would be too expensive.
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
Plant tissue culture is the technique of growing cells, tissue, organ or organism in sterilised nutrient media under controlled aseptic conditions.
Plant cells and organs can be cultured in vitro on a suitable medium. Haberlandt started the technique of plant tissue culture in 1902.
The method of producing thousands of plants through tissue culture is called clonal or micropropagation. Each of these plants will be identical (somaclones).
Culture medium can be liquid or solid. It contains source of carbon and energy (sucrose), minerals, glycine, vitamins, growth regulators (auxin like 2-4 D and cytokinin like BAP).
Plant part used for tissue culture is called explant. The explant and media are sterilized before culturing.
Explants are sterilized by specific antimicrobial chemicals (surface sterilization), while glassware and media can be sterilized by using steam and dry heat.
A small piece of parenchymatous tissue is introduced over culture medium in a tube or flask in dark at 20° - 25°C.
The medium ordinarily contain the auxin, 2, 4 - D, and often a cytokinin like BAP.
After about 2-3 weeks it forms actively growing irregular and undifferentiated mass of cells called callus.
It is divided into several small sections and can be subcultured.
Each piece is then allowed to differentiate into plantlet by providing light and morphogenetic growth hormones.
Multiple Shoot Production :
It is used for raising numerous pathogen free copies of rare plants, hybrids and sterile plants.
A shoot tip or bud with 1 - 4 leaf primordia is sterilised and introduced over culture medium with high salt content and naphthalene acetic acid (NAA).
At intervals of 4 - 6 weeks the shoot tip is given cuts or shaken to form more buds. Each bud gives rise to a small plantlet.
In this technique, explant is suspended into liquid medium containing auxin, 2, 4 - D and is constantly agitated at the speed of 100 - 250 rpm (revolution per minute).
Agitation serves following three purposes :
(i) Aeration of culture
(ii) Constant mixing of medium
(ii) Breakage of cell aggregates into smaller groups.
Suspension cultures grow much faster than callus cultures.
In both the type of tissue cultures, with passage of time, cell/tissue dry matter increases and level of nutrient decreases.
To prevent the damage of newly formed cells, part of the cultures are regularly transferred to new culture vessels containing fresh media. This process is termed as subculturing.
Shoot Tip Culture or Production of Disease Free Plants :
Pathogen free clones of plants can be obtained through shoot-tip culture because shoot apical meristem is usually free of pathogens including virus due to high concentration of auxins and rapid rate of cell division.
The apical meristem accompanied by 1-2 leaf primordia is taken. For this the apical bud is sterilised.
The shoot tip is now placed over culture medium under aseptic conditions. Scientists have succeeded in culturing meristems of banana, sugarcane, potato.
Axillary meristem is also free of virus.
Somatic Embryo Regeneration :
Somatic embryos (embryoids) are embryos that arise from somatic cells in tissue culture.
The pattern of development of a somatic embryo proceed through globular, heart shaped, and torpedo shaped stages and mimic the development of sexually produced embryos.
Somatic embryo regeneration is induced by high concentration of auxin.
These embryos are also used to produce synthetic/ artificial seeds by encapsulating them in alginate.
Embryo Culture :
This involves excision of young embryo from seeds and their cultivation through tissue culture.
Embryo culture has following applications :
(i) In embryo rescue, interspecific hybrids are often sterile because of embryo mortality and seed collapse. In such cases the hybrid embryo is excised from female parent in early stage and is cultured. e.g., hybrid between common bean (Phaseolus vulgaris) and wild bean (P angustissimus).
(ii) Embryo culture allows seedling development in the plants whose seeds lack stored nutrients required for seedling growth. e.g., Orchid.
(iii) Also used in multiplication of some rare plants like makapuno coconuts.
Haploid Culture/Androgenic Haploid Culture/Pollen Grain Culture
This technique was developed by Guha and Maheshwari (1964) in Datura innoxia. The floral buds which are very young and unopened are first sterilized in clorox for 20-40 minutes.
They are then opened to remove anthers. Anthers are introduced over culture medium. Within 4-6 weeks, each anther gives rise to a number of haploid embryoids.
Normally they produce sterile haploid plants. Colchicine treatment results in chromosome doubling and produces homozygous diploids for each and every trait.
Gynogenic haploids are also possible by using unfertilized ovules.
Winter Wheat Jinghua-1 and Rice Guan-18 are two important varieties which are produced by this technique and are now under cultivation.
Uses of Androgenic Haploid
(i) Useful in mutation breeding
(ii) To maintain pure lines
(iii) To produce seedless varieties
Protoplast Fusion/Somatic Hybridisation/Parasexual Hybridisation
It is fusion of protoplasts of two plants belonging to different varieties, species and even genera. The cells are first treated with enzymes pectinase and cellulase.
These enzymes dissolve the cell wall and as a result naked protoplasts are produced.
The naked protoplasts are fused by electrofusion (high frequency alternating electric field with short current pulses) or chemofusion (through sodium nitrate or PEG = polyethyleneglycol).
It results in hybrid protoplasts.
The somatic hybrid may have a synkaryon (single fused nucleus) or heterokaryon (having two unfused nuclei).
The hybrid protoplast is called cytoplasmic hybrid or cybrid if one of the two nuclei of this get degenerated.
The first somatic hybrid was obtained by Carlson et.al. (1972) between Nicotiana glauca and N. langsdorfi (species of Tobacco).
The intergeneric somatic hybrids are Pomato (Potato × tomato) and Bomato (Brinjal and Tomato).
Fig. (a) Protoplast Preparation and (b) Fusion technique
It is ability of a plant cell to give rise to complete plant when cultured in a suitable culture medium at appropriate temperature and aeration conditions.
Each individual vegetative plant cell possess a complete genetic programme required to direct the development of an entire plant.
The term cellular totipotency was used for the first time by a German botanist Gottlieb Haberlandt (1902). He gave the idea that every plant cell is totipotent.
Applications of Tissue Culture
(i) Can be applied for crop improvement.
(ii) Can be applied for the rapid multiplication of desirable and rare plants.
(iii) Can be applied to obtain indefinite number of plants. (Help in micropropagation)
(iv) Can be applied to obtain virus free plants from shoot apex.
(v) Somaclonal Variations :
These variations are produced during tissue culture.
Some of these may be useful and stable e.g., better yield and quality, early maturation, resistance to diseases and pests, etc.
Some of the significant variations which have been taken up in plant breeding are, high protein content and resistance to late blight in Potato, increased shelf life in Tomato, resistance to rust and high temperature tolerance in Wheat, resistance to Tongro Virus and Leaf Hopper in Rice, short duration in Sugarcane etc.