In this section we are dealing with descriptive revision notes of chapter STRATEGIES FOR ENHANCEMENT,IN FOOD PRODUCTION
Biological principles as applied to animal husbandry and
plant breeding have a major role in our efforts to increase
food production. Several new techniques like embryo
transfer technology and tissue culture techniques are going
to play a pivotal role in further enhancing food production.
>9.1 ANIMAL HUSBANDRY
Animal husbandry is the agricultural practice of breeding and raising livestock. As such it is a vital skill for farmers and is as much science as it is art. Animal husbandry deals with the care and breeding of livestock like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats, etc., that
are useful to humans. Extended, it includes poultry farming and fisheries. Fisheries include rearing, catching, selling, etc., of fish, molluscs (shell-fish) and crustaceans (prawns, crabs, etc.). Since time immemorial, animals likebees, silk-worm, prawns, crabs, fishes, birds, pigs, cattle,sheep and camels have been used by humans for products like milk, eggs, meat, wool, silk, honey, etc.
It is estimated that more then 70 per cent of the world livestock population is in India and China. However, it is surprising to note that the contribution to the world farm produce is only 25 per cent, i.e., the productivity per unit is very low.
9.1.1 Management of Farms and Farm Animals
A professional approach to what have been traditional practices of farm
management gives the much needed boost to our food production.
9.1.1.1 Dairy Farm Management
Dairying is the management of animals for milk and its products for
human consumption. In dairy farm management, we deal
with processes and systems that increase yield and improve quality of
milk. Milk yield is primarily dependent on the quality of breeds in the
farm. Selection of good breeds having high yielding potential (under the
climatic conditions of the area), combined with resistance to diseases is
very important. For the yield potential to be realised the cattle have to be
well looked after – they have to be housed well, should have adequate
water and be maintained disease free. The feeding of cattle should be
carried out in a scientific manner – with special emphasis on the quality
and quantity of fodder. Besides, stringent cleanliness and hygiene (both
of the cattle and the handlers) are of paramount importance while milking,
storage and transport of the milk and its products. Nowadays, of course,
much of these processes have become mechanised, which reduces chance
of direct contact of the produce with the handler. Ensuring these stringent
measures would of course, require regular inspections, with proper record
keeping. It would also help to identify and rectify the problems as early
as possible. Regular visits by a veterinary doctor would be mandatory.
9.1.1.2 Poultry Farm Management
Poultry is the class of domesticated fowl (birds) used for food or for their
eggs. They typically include chicken and ducks, and sometimes turkey and
geese. The word poultry is often used to refer to the meat of only these birds,but in a more general sense it may refer to the meat of other birds too.
As in dairy farming, selection of disease free and suitable breeds
proper and safe farm conditions, proper feed and water, and hygiene and
health care are important components of poultry farm management.
9.1.2 Animal Breeding
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 theproduce. A group of animals related by descent and similar in most characterslike general appearance, features, size, configuration, etc.,are said to belong to a breed
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, a superior male is the 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 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 lessdesirable genes. Therefore, this approach, where there is selection at each step, increases the productivity of 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, 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.
Hisardale is a new breed of sheep developed in Punjab by crossing
Bikaneri ewes and Marino rams.
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, e.g., the mule
Controlled breeding experiments are carried out using artificial
insemination. The semen is collected from the male that is chosen as a parent and injected into the reproductive tract of the selected female by the breeder. The semen may be used immediately or can be frozen and used at a later date. It can also be transported in a frozen form to where the female is housed. In this way desirable matings are carried. Artificial insemination helps us overcome several problems of normal matings. Often, the success rate of crossing mature male and female animals is fairly low even though artificial insemination is carried out. To improve chances of successful production of hybrids, other means are also used.
Multiple Ovulation Embryo Transfer Technology (MOET) is one such
programme for herd improvement. In this method, a cow is administered
hormones, with FSH-like activity, to induce follicular maturation and super
ovulation – instead of one egg, which they normally yield per cycle, they produce 6-8 eggs. The animal is either mated with an elite bull or
artificially inseminated. The fertilised eggs at 8–32 cells stages, are
recovered non-surgically and transferred to surrogate mothers. The genetic
mother is available for another round of super ovulation. This technology
has been demonstrated for cattle, sheep, rabbits, buffaloes, mares, etc.
High milk-yielding breeds of females and high quality (lean meat with
less lipid) meat-yielding bulls have been bred successfully to increase
herd size in a short time.
9.1.3 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.
There are several species of honeybees which can be reared. Of these, the
most common species is Apis indica. Beehives can be kept in one’s
courtyard, on the verandah of the house or even on the roof. Bee-keeping
is not labour-intensive.
Bee-keeping though relatively easy does require some specialised
knowledge and there are several organisations that teach bee-keeping.
The following points are important for successful bee-keeping:
(i) Knowledge of the nature and habits of bees,
(ii) Selection of 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 thepollinators of many of our crop species (see chapter 2) 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.
9.1.4 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
fisheries, different techniques have been employed to increase production. For example, through aquaculture and pisciculture we have been able to increase the production of aquatic plants and animals, both fresh-water and marine. Find out the difference between pisciculture and aquaculture. This has led to the development and flourishing of the fishery industry, and it has brought a lot of income to the farmers in particular and the country in general. ‘Blue Revolution’ as being implemented along the same lines as ‘Green Revolution’.
9.2 PLANT BREEDING
Plant breeding as a technology has helped increase yields to a very large extent. Who in India has not heard of Green Revolution which was responsible for our country to not merely meet the national requirements in food production.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.
9.2.1 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 civilisation;
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 hybridisation 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, drought), resistance to pathogens
(viruses, fungi and bacteria) and increased tolerance to insect pests would
be on our list too
Plant breeding programmes are carried out in a systematic way
worldwide–in government institutions and commercial companies. The
main steps in breeding a new genetic variety 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 desirable combination of characters.
The selected plants are multiplied and used in the process of
hybridisation. Purelines are created wherever desirable and possible.
(iii) Cross hybridisation 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 nee to be combined with disease resistance from another parent. This is possible by cross hybridising 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 male parent have to be collected and placed on the stigma of the flowers selected as female parent . 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 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 commercialisation 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 fertiliser 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
agroclimatic 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 per cent of India’s GDP and employs nearly
62 per cent 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 farm land. 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.
Semi-dwarf rice varieties were derived from IR-8, (developed at International Rice Research Institute (IRRI), Philippines) and Taichung Native-1 (from Taiwan). The derivatives were introduced in 1966. Later better-yielding semidwarf varieties Jaya and Ratna were developed in India
Sugar cane: Saccharum barberi was originally grown in north India, but
had poor sugar content and yield. Tropical canes grown in south India
Saccharum officinarum had thicker stems and higher sugar content but
did not grow well in north India. These two species were successfully
crossed to get sugar cane varieties combining the desirable qualities of
high yield, thick stems, high sugar and ability to grow in the sugar cane
areas of north India.
Millets: Hybrid maize, jowar and bajra have been successfully developed
in India. Hybrid breeding have led to the development of several high
yielding varieties resistant to water stress.
9.2.2 Plant Breeding for Disease Resistance
A wide range of fungal, bacterial and viral pathogens, affect the yield ofcultivated crop species, especially in tropical climates. Crop losses can
often be significant, up to 20-30 per cent, or sometimes even total. In this
situation, breeding and development of cultivars resistant to disease
enhances food production. This also helps reduce the dependence on use of fungicides and bacteriocides. 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, 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 hybridisation and selection. It’s steps are essentially
identical to those for breeding for any other agronomic characters such
as high yield. The various sequential steps are : screening germplasm for resistance sources, hybridisation of selected parents, selection and
evaluation of the hybrids and testing and release of new varieties
Conventional breeding is often constrained by the availability of limited
number of disease resistance genes that are present and identified in various crop varieties or wild relatives. Inducing mutations in plants through diverse means and then screening the plant materials for resistance sometimes leads to desirable genes being identified. Plants having these desirable characters can then be either multiplied directly or can be used in breeding. Other breeding methods that are used are selection amongst somaclonal variants and genetic engineering.
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 desirable character as a source in breeding – this process is called mutation breeding. In mung bean, resistance to yellow mosaic virus and powdery mildew were induced by mutations.
Several wild relatives of different cultivated species of plants have been
shown to have certain resistant characters but have very low yield. Hence,
there is a need to introduce the resistant genes into the high-yielding
cultivated varieties. Resistance to yellow mosaic virus in bhindi
(Abelmoschus esculentus) was transferred from a wild species and
resulted in a new variety of A. esculentus called Parbhani kranti.
All the above examples involve sources of resistance genes that are in
the same crop species, which has to be bred for disease resistance, or in a
related wild species. Transfer of resistance genes is achieved by sexual
hybridisation between the target and the source plant followed by
selection.
9.2.3 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.
9.2.4 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 for 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.
9.3 SINGLE CELL PROTEIN (SCP)
Conventional agricultural production of cereals, pulses, vegetables, fruits,
etc., may not be able to meet the demand of food at the rate at which
human and animal population is increasing. The shift from grain to meat
diets also creates more demand for cereals as it takes 3-10 Kg of grain to
produce 1 Kg of meat by animal farming. Can you explain this statement
in the light of your knowledge of food chains? More than 25 per cent of
human population is suffering from hunger and malnutrition. One of the
alternate sources of proteins for animal and human nutrition is Single
Cell Protein (SCP).
Microbes are being grown on an industrial scale as source of good
protein. Blue-green algae like Spirulina can be grown easily on materials
like waste water from potato processing plants (containing starch), straw,
molasses, animal manure and even sewage, to produce large quantities
and can serve as food rich in protein, minerals, fats, carbohydrate and
vitamins. Incidentally such utilisation also reduces environmental
pollution.
Certain bacterial species like Methylophilus methylotrophus, because
of its high rate of biomass production and growth, can be expected to
produce 25 tonnes of protein. The fact that edible mushrooms are eaten
by many people and large scale mushroom culture is a growing industry makes it believable that microscopic fungi too would become acceptable as food.
9.4 TISSUE CULTURE
As traditional breeding techniques failed to keep pace with demand and
to provide sufficiently fast and efficient systems for crop improvement,
another technology called tissue culture got developed. It was learnt by scientists, during 1950s, that whole plants could be regenerated from explants, i.e., any part of a plant taken out and grown in a test tube, under sterile conditions in special nutrient media. This capacity to generate a whole plant from any cell/explant is called totipotency. You will learn how to accomplish this in higher classes. It is important to stress here that the nutrient medium must provide a carbon source such as sucrose and also inorganic salts, vitamins, amino acids and growth regulators like auxins, cytokinins etc. By application of these methods it is possible to achieve propagation of a large number of plants in very short durations. This method of producing thousands of plants through tissue culture is called micropropagation. Each of these plants will be genetically identical to the
original plant from which they were grown, i.e., they are somaclones.
Many important food plants like tomato, banana, apple, etc., have been
produced on commercial scale using this method.
Another important application of the method is the recovery of
healthy plants from diseased plants. Even if the plant is infected with a
virus, the meristem (apical and axillary) is free of virus. Hence, one
can remove the meristem and grow it in vitro to obtain virus-free plants.
Scientists have succeeded in culturing meristems of banana, sugarcane,
potato, etc.
Scientists have even isolated single cells from plants and after
digesting their cell walls have been able to isolate naked protoplasts
(surrounded by plasma membranes). Isolated protoplasts from two
different varieties of plants – each having a desirable character – can be
fused to get hybrid protoplasts, which can be further grown to form a
new plant. These hybrids are called somatic hybrids while the process
is called somatic hybridisation. Imagine a situation when a protoplast
of tomato is fused with that of potato, and then they are grown – to form
new hybrid plants combining tomato and potato characteristics. Well,
this has been achieved – resulting in formation of pomato; unfortunately
this plant did not have all the desired combination of characteristics for
its commercial utilisation
