Plant Breeding | Biology for Grade 12 PDF Download

Plant Breeding

Genetic Improvement and Development of New Varities

Trait : Trait or character is any morphological, anatomical, biochemical or behavioural feature of an organism.

Variety : A group of plant that has the same genotype, but it differs for one or more characters from other varieties of the same crop. An improved variety is superior to the other existing varieties of the same crop in one or more characters.

Plant breeding :- The branch of agricultural sciences which leads to development of new and improved variety of crop plant. It is the purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yield and have disease resistance.

It was started about 9000-11000 year ago.

1871 – Department of Agriculture, I^st time organized.

1905 – Imperial Agriculture Research Institute Pusa (IARI), Bihar.

1936 – Rebuilt in Delhi with same name.

1946 – Name changed to Indian Agriculture Research Institute, Pusa

Objective of plant breeding :

1.   Development of high productivity crop variety.

2.   Development of variety with high nutritional quality.

3.   Development of variety with high water use efficiency.

4.   Development of variety with high mineral use efficiency.

5.   Development of abiotic stress (Drought, Salinity) tolerant variety.

6.   Development of biotic stress and insect pest resistant variety.

7.   Development of early maturing variety.

8.   Development of variety with less post harvest loss.

Some plant breeding institute

1.  I.A.R.I.   - Indian agricultural research institute, Pusa, New Delhi

2.   C.P.R.I. -  Central potato research institute, Shimla

3.   C.R.R.I. - Central rice research institute, Cuttack

4.   I.S.B.R.I.  -  Indian sugarcane breeding research institute, Coimbatore

5.   C.A.Z.R.I.-  Central arid zone research institute, Jodhpur

6.   N.B.R.I.  -  National botanical research institute, Lucknow

7.   N.B.P.G.R. -  National bureau of plant genetic resources, New Delhi

8.   I.I.S.R.-   Indian institute of spice research, Calicut

9.   I.R.R.I.   -   International rice research institute Manila

10.  I.C.R.I.S.A.T. - The International Crops Research Institute for the Semi-Arid Tropics

11.  C.Y.M.M.I.T.   -   International Maize and Wheat Improvement Center

Some plant Breeder :

1.   Normon E. Bourloug : Father of green revolution. He developed semi dwarf varieties of wheat Sonara 64 and Lerma rojo.    He got Nobel Peace Prize in 1970.

2.   N.I. Vavilov : Father of centre of origin concept for cultivated plants.

3.   M.S. Swaminathan : Father of green revolution in India. Father of mutational breeding in India.
He developed semi dwarf varieties of wheat Sharbati Sonara and Pusa Lerma through mutation from Sonara 64 and Lerma rojo, respectively. He was the I^st Winner of World Food Prize.

4.   Gurdev Singh Khush :  Former director of IRRI. He is a rice breeder. He developed high yielding rice variety IR-36. He got World Food Prize.

5.   S.K. Vasil : Maize Breeder. He developed biofortified maize varieties (QPM) which are having high concentration of Tryptophan and Lysine. He got World Food Prize.

1.   Collection of variability.

2.   Evaluation and Selection of parents.

3.   Cross hybridization among the selected plant.

4.   Selection and testing of superior recombinants.

5.   Testing release and commercialization of new cultivar.

(1) 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 population.

The entire collection (of plants/seeds) having all the diverse alleles for all genes in a given crop is called germplasm collection.

(2)  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.

(3)  Cross hybridisation among the selected parents: The desired characters have very often to be combined from two different plants (parents). 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.

(4)  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. 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.

(5) Testing, release and commercialization of new cultivars: The newly selected lines are evaluated for their yield and other agronomic traits of quality, disease resistance, etc. This evaluation is done by growing these in the research fields and recording their performance under ideal 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 agro-climatic zones where the crop is usually grown. The material is evaluated in comparison to the best available local crop cultivar – a check or reference cultivar. If material is superior than best crop cultivar, then it is released for cultivation by ICAR.

Wheat and Rice : During the period 1960 to 2000, wheat production increased from 11 million tones 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 semi-dwarf 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.

Methods of New Variety Development:

(1)  Domestication             

(2)  Germplasm collection & conservation

(3)  Plant introduction       

(4)  Hybridisation

(5)  Polyploidy                  

(6)  Mutational breeding

(7)  Genetic engineering

(1)  Domestication :- All the present species of cultivated plants are of wild type species in origin. Process of cultivation of wild species in order to fulfill human need is called domestication of plant. Many present day crops are the result of domestication in ancient times.

• Genetic diversity is the occurrence of large number of varieties, biotypes, variations and alleles.
• Greatest genetic diversity of plants is found in their natural home lands.
• Germplasm collections are made mostly from an area, where wild relatives of crop plants still live.
• Genetic diversity refers to intra-specific and inter-specific variation.
• Vavilov (1926) proposed that different crop plants originated in different areas, where their wild relatives are present and genetic diversity is maximum. 
• Vavilov proposed 8 centre and 3 subcentre (11 centre) of origin. He collected 26,000 varieties of wheat.
• Presently, 12 centre of origin is present. Australia is the 12^th centre.
• Cotton has developed in both old and new world.
• The original homeland of some important crops are listed below :-

Natural home :- It is the centre of origin of a crop, which often abounds in its wild relatives and maximum genetic diversity.

Secondary home :- It is the major centre of production of a crop plant, which is away from centre of origin and lacks wild relatives.

Wild relatives :- Species related to cultivated plant that occur in the wild in areas of their origin.

(2)  Germplasm collection & conservation :- 

Germplasm is the sum total of all the alleles of the genes present in cell of a crop species 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.

It is consist of –

(i)  Cultivated improved varieties.

(ii)  Improved varieties that are no more cultivated.

(iii) Old local or desi varieties.

(iv) Varieties produced by plant breeders (undistributed).

(v) Wild species related to the crop species.

The sum total of different types of all the genes and their alleles present in a population is called gene pool. The gene pool of a population is not static.

Genetic erosion – The loss of genes from a gene pool is called genetic erosion.

Genetic erosion occurs due to deforestation, urban expansion, damage to ecosystem and adoption of genetically uniform modern variety of crops. 

11 million hectares of tropical forest disappear every year.

There are four basic way to conserve plant germplasm. 

(i)   Conservation of plant in wild state i.e. in natural habitat like forests.

(ii)  Conservation of plant in botanical gardens.

(iii) Introduction of plant for cultivation in agriculture and horticulture.

(iv) Preservation of plants in seed form or some other suitable form.

Method of genetic conservation :     

(i)   In-situ conservation – It means maintenance of biological diversity in natural habitats like forests and natural reserve like national park, wildlife sanctuaries and bio-sphere reserves. In situ conservation of wild plants help in protecting species threatened with extinction.

(ii)  Ex-situ conservation – It is the conservation of selected or rare plant in a place outside the natural home. In this conservation rare or selected plant material are grown in specific gardens.

Ginkgo biloba plant is preserved by Ex-situ conservation.

Ex-situ conservation includes offsite collections and gene bank.

(a)  Offsite collection : They are living collections of wild and domesticated species in botanical garden, zoo etc.

(b)  Gene bank : The place or institution, where different plant material (genes) are kept or preserved, is called ''Gene bank''.

In gene bank, storage of germplasm is done either in the form of seed or vegetative material, but best and convenient way is storage of seed.

Seed means, any plant part that is used to grow a crop. Thus ‘seed’ would include grains of wheat, rice, tubers of potato, stem of sugarcane etc. which are used for producing new plants.

Cryopreservation :- Preservation of germplasm at ultra low temperature at –196° C (liquid nitrogen) called cryopreservation.

Storage of dry seeds is done at low temperature (–10 to –20°C), because under these conditions the metabolic activities are minimum, prevent their germination.

Seeds are of two types-

(a)  Orthodox seed :- The seeds cannot be killed or damaged as a result of decrease in moisture content& temperature. e.g. seeds of wheat, rice, maize, oat barley (Cereals) and also different pulses or legumes.

(b)  Recalcitrant seeds :- The seeds which can be killed or damaged as a result of drying and decrease in temperature. These can be stored for a short span. eg. seeds of rubber, tea, coconut, Jack fruit (Artocarpus), litchi, oil palm etc.

Conservation of crop with recalcitrant seed, can be made by in situ conservation method and also by tissue culture method.

Plants with recalcitrant seed are grown in orchard, where all possible strains and varieties are maintained.

Storage of germplasm by tissue culture :

The tissue culture technique for storage of germplasm is used in case where :-

(a)  No seeds are produced (banana, sugar cane).

(b)  Non viable seeds.

(c)  Crop with recalcitrant seed.

(d)  Specific clone is to be maintained.

Best method of tissue culture for germplasm storage is ''Shoot tip culture''. 

Shoot tip culture rapidly, becoming preferred material for international exchange of germplasm as they are more stable, easier to regenerate in to whole plants and produce virus free clonal plants.

Nowadays germplasm of potato, Cassava, and banana are exchanged by this method.

The main advantage of tissue culture storage of germplasm are :-

(a)  Economical

(b)  Requires small area for storage of many genotype

(c)  Can be used for multiplication of rare and endangered species. 

Significance of germplasm of wild species :

It is very important to conserve wild species of plant as these are highly resistant to insects, pests, disease and unfavourable growth conditions, which are necessary for survival of plants.

The loss of wild plants, will reduce the genetic variability and will be a great loss to gene pool.

Potato and sugarcane has been improved by use of germplasm of wild species having many characters like disease resistance and resistance to environmental stress.

In potato (Solanum tuberosum) gene for resistance to potato virus-X and potato leaf roll virus have been obtained from a wild species ''Solanum acaule''. 

Resistance to wilt fungus (Fusarium) and cyst nematode (Globodera) has been introduced from ''Solanum spegazzini''. 

Potato got resistant gene to potato virus–Y from a wild relatives ''Solanum stoloniferum'' 

Resistance to late blight of potato (Caused by fungus Phytophthora infestans) has been derived from ''S.demissum'' 

Similarly, sugarcane (Saccharum officinarum) got resistance to red rot of sugarcane and adverse environment from a wild species ''Saccharum spontaneum''. 

INTERNATIONAL EFFORTS FOR UTILIZATION OF CROP - Germplasm

Cereals (rice, wheat, maize, rye, sorghum, bajra etc.) are the main sources of food for human population in the world and rice alone constitutes staple food of more than 50% world's population.

Improvement in rice production :

Dwarfing gene of rice ''dee-geo-woo-gene'' was obtained from Taiwan.

This gene was incorporated to produce high yielding early maturing IR-8 and IR-24 varieties by IRRI, Manila.

Gurdev S.khush and his team crossed 13 varieties of rice from six countries and wild rice Oryza nivara (from India) to develop IR-36 variety of rice.

IR-36 variety of rice is resistance to grassy stunt virus.

IR-36 is the high yielding variety of rice and has solved major food problem in Asia.

Improvement in wheat production :

Dr. N.Borlaug (Mexican wheat breeder) develop many dwarf wheat varieties like Sonora-64 & Lerma rojo by incorporating Norin-10 (Japanese dwarf gene) gene. 

(3)  Plant introduction - 

This is the most rapid method of crop improvement. 

The process of introducing plants with specific characters from one area to a new and changed climatic condition is called ''Plant introduction''. 

(a)  If plants are introduced from foreign country, it is called ''exotic collection (EC).

(b)  If plants are brought from same country then it is called ''indigenous collection'' (IC).

Primary introduction :- If introduced plants may be used directly for cultivation, it is called primary introduction.

Secondary introduction :- If introduced plants may be used for cultivation after subjecting to selection/hybridization, it is called secondary introduction.

Acclimatization :

It means adaptation of introduced plant material in the changed or new climatic conditions is called acclimatization.

Plant Quarantine :

Introduced plant material are subjected to ''Quarantine laws/plant protection inspection. To check the entry of pathogen, all the introduced plant materials is thoroughly inspected for contamination of weeds, diseases and insect pest. This testing is known as plant quarantine.

If the plant material is found suitable, phytosanitary certificates are issued and only then the plant material is introduced in our country.

Uncontrolled plant introduction in the past are responsible for introduction of hazardous diseases like late blight of potato, leaf rust of coffee, fire blight of apple, bunchy top of banana etc.

Many weeds like Argemone maxicana, Eicchornia crassipes and Parthenium argentatum etc. introduced in our country due to uncontrolled plant introduction.

New plants like potato, groundnut, coffee, rubber, guava, grapes, papaya, litchi, gulmohar, bougainvillea etc are the result of plant introduction.

Wheat variety ''Ridley was introduced in India from Australia.

Many improved varieties of different crop plants are also outcome of these introduction e.g Sonora-64 varieties of wheat, Plametto varieties of soyabeans, Kent variety in Oat, Tiachung native 1 (TN1) of rice etc.