Breed

A breed is a group of animals that is consistent enough in type to be logically grouped together, and that when mated within the group reproduce the same type.

Context

1. Animal Breeding. 
2. Plant Breeding. 

       

 1. Animal breeding 

  Controlled mating followed by selection in order to obtain superior genotypes of domesticated animals is known as animal breeding. The chief objectives of the animal breeding are

 (i) Increased yield like that of milk, eggs, meat and wool. 

(ii) Better quality of animal products like milk, eggs, meat and wool. 

(iii) Higher growth rate. (iv) Better assimilation efficiency. 

(v) Resistance to various diseases.

(vi) Longer productive life. 

(vii) Higher acceptable reproductive rate. Animal breeding is of two types, inbreeding and out-breeding.

1. Inbreeding

Inbreeding is mating between close relatives, like individuals of the same animal breed, for 4-6 generations. Normally mating within the same breed is strictly cross fertilisation because of

 (i) Occurrence of male and female individuals 
(ii) Highly heterozygous nature.

             Therefore, mating between members of the same breed can also help in genetic improvement. Superior cows (females) and superior bulls (males) of the same breed but preferably of different populations are mated in pairs. The progeny is evaluated and the superior males and females are selected for further mating. A superior is evaluated and the super deed but preferably of differencing. Superior cow (femalenating female like cow is the one which gives more milk per lactation. A superior male like bull is the one which series a superior progeny as compared to other males.

However, continued inbreeding within relatives of 4-6 generations tends to increase homozygosity.

population leads to decreased vigour, fitness, fertility and productivity. It is called inbreeding depression.

Some harmful recessive alleles are eliminated on becoming homozygous due to selection. Some superior . Some superior alleles accumulate while less desirable alleles are eliminated during selection for superior progeny. This method of animal breeding, therefore, increases productivity of inbred population. Rather every breed creases productivituuring selection for sure has developed through various degree of inbreeding. But continued inbreeding within the small local

population with the superior animal of another population belonging to the same breed.

2. Outbreeding. 

It is mating between unreiated animals which may belong to same breed, different breeds of the same species and different species. Accordingly outbreeding is of three types -outcrossing, cross breeding and interspecific hybridisation.

(i) Outcrossing.
 It is the practice of mating between unrelated members of the same breed. They do not have common ancestors on either sides for 4-6 generations. Outcrossing overcomes inbreeding depression, infuses vigour vitality and increased growth rate. It enhances productivity like milk, wool and meat yield. An offspring formed in outcrossing is called outcross.

(ii) Cross Breeding.
It is the mating between animals of different breeds. Cross breeding is accomplished for either developing new superior breeds or improving the local breeds. In the former strategy superior males of one breed having one set of desirable traits are crossed to superior females of another breed having second set of desirable traits. The hybrid progeny will have the desirable traits of both the breeds. It may be used directly for commercial production or subjected to some form of inbreeding and selection to develop a new stable superior breed.

      For improvement of local breeds , cows of the local breeds (inferior breeds ) are mated to bulls of superior exotic breeds. In each progeny the cows are mated to bulls of the same superior breeds . In 6-7 generations, superior breeds which are disease resistant, hardy and acclimatised to local conditions are produced, e.g., Sunandini, Karan Swiss. A new breed of sheep called Hisardale has been developed through crossbreeding Bikaneri ewes with merino rams.

The techniques of gene transfer and cloning (buffalo Garima, 2009) are also being tried.

(iii). Interspecific Hybridisation.

Interspecific hybrids are generally sterile in case of domestic animals. They cannot be converted into fertile forms through chromosomal doubling. Therefore, interspecific hybridisation is performed in animal breeding only when the sterile hybrid is far superior to either of the parents and is, therefore, economically very important. Mule (cross between male donkey and female horse) is both hardier and sturdier than either of its parents. It is used for transport of heavy articles on difficult mountainous terrains.

     

 2. Plant Breeding

 Traditional farming has been unsuccessful in meeting biomass requirement of humans and domesticated animals. As a result famines have been quite common in older times. Increase in crop area helped a bit but it was at the cost of forested area. Better management practices like certified seeds, fertilizers, irrigation, improved cropping pattern and use of pesticides also increased the crop yield but only to a limited extent which was insufficient to meet the requirement of rapidly growing human population. It was green revolution which made India as well as many other countries surplus in food grains. Green revolution is the rapid increase in agricultural output in India during 19601980 golden era) due to better management, development of high yielding and disease resistant varieties of major cereals- Wheat, Rice and Maize

The major characters which are incorporated in new varieties are high yield and improved qualin Other important characters sought to be improved are resistance to pathogens (mainly viruses, bacteria fungi) and pests (insects, nematodes, etc.) and increased tolerance to adverse environmental condition like salinity, drought, low or high temperature. However, development of new varieties is not an eas job. It takes several years of labour on the part of several workers. For example, twelve years were spent in developing Wheat variety HUW-468. Plant breeding for development of new varieties is carried out in a systematic way by government agencies, agriculture universities and commerical companies. The various steps that were required for developing the new varieties were as follows:

1. Collection of Variability. Availability of whole range of genetic variability is the backbone of any breeding programme. Procuring the whole range of genetic variability of a crop plant is called germplasm collection. Germplasm is the sumtotal of various possible alleles of all the genes present in all the present and past varieties of a crop, its wild relatives and related species. Germplasm of a crop plant, therefore, consists of 

(i) All present day cultivated improved varieties.

(ii) All improved varieties which are no longer being cultivated now.

(iii) Old local (desi) varieties of all areas.

(iv) Pure lines produced by plant breeders.

(v) Wild relatives/species of the crop species.

Germplasm collection is made from within the country as well as from other countries. It is carried out under the guidance of International Board of Plant Genetic Resources (IBPGR) established in 1971. The board has set up several centres. One such centre is ICRISAT (International Crops Research Institute for Semi-arid Tropics) at Hyderabad. It is responsible for collection and conservation of germplasm of Chick Pea, Pigeon Pea, Groundnut, Pearl Millet and Sorghum. India has several other centres where germplasms of important crop plants are conserved. Central Institute of Cotton Research (CICR) has germplasm of over 4000 varieties and 28 species of Gossypium. Similar institutes are Central Potato Research Institute (CPRI), Central Rice Research Institute (CRRI), Sugarcane Breeding Institute (SBI), etc. Germplasm collections are made under supervision of National Bureau of Plant Genetic Resources (NBPGR). A good germplasm collection is essential for developing desirable improved varieties. Germplasm collections are conserved live in seed gene banks. 

Orthodox seeds are kept at a low temperature of -10° to -20°C under anaerobic conditions. As percentage seed germination decreases with time, the stored seeds are periodically germinated to obtain fresh seeds from the plants formed by them. Recalcitrant seeds can be stored only under aerobic humid conditions at room temperature for shorter duration. Their germplasm is generally conserved as live plants in orchards and gardens along with fruit trees. All types of germplasm can be stored and conserved as shoot cultures in tissue culture laboratories. It can also be cryopreserved.

2. Evaluation and Selection of Parents. The whole available germplasm is screened for desirable traits required to be incorporated into the new variety. Two or more types of plants are selected which possess all the required traits amongst them.

The plants having the desired traits are called parents. They are selfed to bring about homozygosity,

Defective plants are discarded. As the defective plants stop appearing, a breeding line or parent with similar genotype is ready. Out of the two types of the parents, some plants are marked as female while others are marked as male. There is no such need in case of unisexual plants.

3. Cross-Hybridisation Amongst Selected Parents. Hybridisation is carried out between parents with desired characters to be genetically combined in the new variety, e.g., high protein quality and disease resistance. It is carried out by the following method

(i) Bagging. As soon as floral buds appear, the same are covered with polythene bags.

(ii) Emasculation. The flowers of plants selected as females are opened in the bud condition and their anthers removed carefully. The practice is called emasculation. It checks the chances of self pollination. Pollen grains are also killed in such flowers by dipping in water at 50°C for ten minutes, or spraying with inhibitor like maleic hydrazide.

(iii) Crossing. Pollen grains of plants selected as male are collected in clean tubes or containers after removing their covering polythene bag. The collected pollen grains are then dusted over the stigmas of emasculated flowers of female' plants. After performing artificial pollination, the flowers are covered again by polythene bags so as to prevent contamination from foreign pollen.

(iv) Desired Combination of Variations. The seeds obtained from artificially cross-pollinated flowers of female plant are called hybrid or F; seeds. F2 and Fz and later generations are raised from them to know the availability of desired variations. Finding the right combination of desirable characters is a laborious task. For this hundreds and thousands of plants are screened. It is just luck that such a combination may be found out. If the result is negative, back crossing is carried out with the parent whose desired traits are not incorporated.

4. Selection and Testing of Superior Recombinants. It is an important step for bringing about improvement of crop. The sceds of only those plants which have desirable traits are taken up for raising the next generation. All other plants are rejected. Differential reproduction of a phenotype having desirable traits is called selection. For example, hybridisation has been carried out for obtaining rice grains of larger size. In the population raised from F, or F2 seeds, some plants will have extra long grains, long grain, medium sized grains and short grains. Only the seeds having extra long grains are picked up for raising the next generation. In the next generation, selection is made again for extra long grain size. The process is continued till the whole population of extra long grain size is obtained.

Selection is different in self pollinated and cross pollinated crops.

(a) Selection in Self Pollinated Crops. The amount of cross pollination is low, hardly 5%. Even the parents are homozygous. Therefore, hybridisation produces heterozygosity in only a few characters. As selection is made at each generation for the superior aits, the latter become converted into homozygous state after a few generations. It produces the d sired genotype or pure line. HUW-468 is one such homozygous genotype. Such genotypes are maintained through self pollination year after year. Variations appearing in such crops are mostly due to environment or occasional mutations.

(b) Selection in Cross-Pollinated Plants. They are generally heterozygous for most of their traits.

Homozygosity cannot be maintained because of cross pollination. Therefore, heterozygosity is allowed to operate in the new variety. Selection is made of a large number of plants with superior traits. Their seeds are grown together. In the next generation, selection is again made of a number of plants for superior traits. By this method the population through highly heterozygous, comes to have many different superior genotypes after a few generations.

5. Testing, Release and Commercialisation of New Cultivars. The newly developed varieties are tested for the amount of yield, quality of yield, duration, effect of weather, disease and insect resistance, under ideal fertilizer application, irrigation and other crop management practices. This is done by Indian Council of Agriculture Research (ICAR), New Delhi. For every type of crop the country is divided into 2-8 agro climatic zones on the basis of soil and climate conditions. All the recently developed varieties of the same crop are evaluated together at several locations in different agroclimatic zones first in research fields and then farmers' fields consecutively for atleast three years. The performance of new varieties are compared with old varieties as well as amongst themselves for various aspects. The material which is superior to others is listed. The breeder then proposes its release as a new variety. The proposal is then examined by a variety release committee. If found suitable, the material is given a name and allowed to be released as a new variety. The same is notified by the government.

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