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PLANT GENETIC RESOURCES
- The sum total of genes in a crop species is referred to as genetic resources. or
- Gene pool refers to a whole library of different alleles of a species
or
- Germplasm may be defined as the sum total of hereditary material i.e., all the alleles of various genes present in a crop species and its wild relatives.
- Also known as:
- gene pool or
- genetic stock or
- germplasm or
- genetic resources.
- Germplasm or gene pool is the basic material with which a plant breeder has to initiate his breeding programme.
- Important features of plant genetic resources are :
✓ Gene pool represents the entire genetic variability or diversity available in a crop species. ✓ (^) Germplasm consists of land races, modern cultivars, obsolete cultivars, breeding stocks, wild forms and wild species of cultivated crops. ✓ Germplasm includes both cultivated and wild species or relatives of crop plants. ✓ Germplasm is collected from the centres of diversity, gene banks, gene sanctuaries, farmers fields, markets and seed companies. ✓ Germplasm is the basic material for launching a crop improvement programme.
✓ Germplasm may be indigenous (collected with in country) or exotic (collected from foreign countries)
Kinds of Germplasm :
- The germplasm consists of various plant materials of a crop such as: (1) land races (2) obsolete cultivars (3) modern cultivars (4) advanced (homozygous), breeding materials (5) wild forms of cultivated species (6) wild relatives (7) mutants These are briefly discussed below :
- Land races :
✓ These are nothing but primitive cultivars which were selected and cultivated by the farmers for many generations without systematic plant breeding efforts. ✓ Land races were not deliberately bred like modern cultivars. They evolved under subsistence agriculture. ✓ Land races have high level of genetic diversity which provides them high degree of resistance to biotic and abiotic stresses. ✓ Land races have broad genetic base which again provides them wider adoptability. ✓ The main drawbacks of land races are that they are less uniform and low yielders. ✓ Land races were first collected and studied by N.I. Vavilor in rice.
- Obsolete Cultivars: ✓ These are the varieties developed by systematic breeding effort which were popular earlier and now have been replaced by new varieties.
✓ These lines which are not yet ready for release to farmers. They often contain valuable gene combinations.
- Wild forms of cultivated species :
✓ Wild forms of cultivated species are available in many crop plants. Such plants have generally high degree of resistance to biotic and abiotic stresses and are utilized in breeding programmes. ✓ They can easily cross with cultivated species. Wild forms of many crop species are extinct.
- Wild Relatives :
✓ Those naturally occurring plant species which have common ancestry with crops and can cross with crop species are referred to as wild relatives or wild species. ✓ Wild relatives include all other species, which are related to the crop species by descent during their evolution. ✓ Both these groups are sources of valuable genes for biotic and abiotic stress and for quality traits and yield.
- Mutants :
✓ Mutation breeding is used when the desired character is not found in the genetic stocks of cultivated species and their wild relatives. ✓ Mutations do occur in nature as well as can be induced through the use of physical and chemical mutagens. ✓ The extra variability which is created through induced mutations constitutes important components of genepool. ✓ Mutant for various characters sometimes may not be released as a variety, but they are added in the genepool. ✓ The germplasm includes those carrying gene mutations, chromosomal aberrations and markers genes etc. are considered special genetic stocks. They are useful in breeding programmes.
The gene pool system of classification
- The pool of a crop includes all cultivars, wild species and wild relatives containing all the genes available for breeding use.
- Based on degree of relationship, the gene pool of crops can be divided into three groups (Harland and Dewet, 1971), viz.,
- Primary gene pool
- Secondary Gene pool
- Tertiary gene pool These are briefly discussed below :
- Primary gene pool (GP1) :
✓ This is also known as gene pool one (GP1). ✓ The gene pool in which intermating is easy and leads to production of fertile hybrids is known as primary gene pool. ✓ It includes plants of the same species or of closely related species which produce completely fertile offspring on intermating. ✓ In such gene pool, genes can be exchanged between lines simply by making normal crosses. ✓ This is the material of prime breeding importance.
- Secondary gene pool (GP2) :
✓ (^) This type of gene pool is also known as gene pool two (GP2). ✓ The genetic material that leads to partial fertility on crossing with GP1 is referred to as secondary gene pool. It includes plants that belong to related species. ✓ Such material can be crossed with primary gene pool, but usually the hybrids are sterile and some of the progeny to some extent are fertile. ✓ Transfer of gene from such material to primary gene pool is possible but difficult.
3.Tertiary gene pool (GP3) :
✓ The storage is for medium duration, i.e., 10-15 years. These collections are actively utilized in breeding programme. ✓ These collections are used for evaluation, multiplication and distribution of the accessions. They are usually maintained by multiplying the seeds of their own accessions. ✓ But from time to time, base collection material should be used for regeneration of these collections. Germination test is carried out after every 5-10 years to assess the reduction in seed viability.
3. Working collections :
✓ The accessions being actively used in crop improvement programmes constitute working collection.
✓ Their seeds are stored for 3-5 years at less than 15 0 C and they
usually contain about 10% moisture.
✓ These collections are maintained by the breeders using them.
Core collection :
✓ The concept of core collection was proposed by Frankel it refers to a subset of base collection which represents the large collection.
✓ Or a limited set of accessions derived from an existing germplasm collections. Germplasm activities : There are six important activities related to plant genetic resources.
- Exploration and collection
- Conservation
- Evaluation
- Documentation
- Multiplication and Distribution
- Utilization
1.Exploration :
✓ Exploration refers to collection trips and collection refer to tapping of genetic diversity from various sources and assembling the same at one place.
✓ The exploration and collection is a highly scientific process. This process takes into account six important items, viz, (1) sources of collection, (2) priority of collection, (3) agencies of collection, (4) methods of collection, (5) methods of sampling and (6) sample size. Merits and Demerits : There are several merits and demerits of exploration and collection of germplasm, some of which are as discussed below:
Merits :
✓ Collection helps in tapping crop genetic diversity and assembling the same at one place.
✓ It reduces the loss of genetic diversity due to genetic erosion.
✓ Sometimes, we get material of special interest during exploration trips.
✓ Collection also helps in saving certain genotypes from extinction.
Demerits :
✓ (^) Collection of germplasm especially from other countries, sometimes leads to entry of new diseases, new insects and new weeds.
✓ Collection is a tedious job.
✓ Collector, sometimes has encounter with wild animals like elephants, tigers etc.
✓ Transportation of huge collections also poses difficulties in the exploration and collection.
- Germplasm conservation :
✓ Conservation refers to protection of genetic diversity of crop plants from genetic erosion. There are two important methods of germplasm conservation or preservation. or
✓ The risks associated with ex situ conservation are not operative.
- Ex situ conservation :
- Conservation of germplasm away from its natural habitat is called ex situ germplasm conservation.
- Preservation in the form of seed is the most common and easy method, relatively safe, requires minimum space and easy to maintain.
- Glass, tin or plastic containers are used for preservation and storage of seeds. The seed can be conserved under long term, medium term and short term storage conditions.
Advantages:
✓ It is possible to preserve entire genetic diversity of a crop species at one place.
✓ Handling of germplasm is also easy
✓ This is a cheap method of germplasm conservation
- Roberts in 1973 classified seeds on the basis of their storability, into two major groups. viz.,
- Orthodox seeds
- Recalcitrant seeds 1. Orthodox Seeds :
✓ Seeds of this type can be dried to low moisture content of 5% and stored at a low temperature without losing their viability are known as orthodox seeds. ✓ Most crop seeds belong to this category. Such seeds can be easily stored for long periods; their longevity increases in response to lower humidity and storage temperature. ✓ Eg. Wheat, Rice, Corn, Chickpea, Cotton, Sunflower
- Recalcitrant seeds :
✓ The viability of this group of seeds drops drastically if their moisture content is reduced below 12-30%. ✓ Seeds of many forest and fruit trees, and of several tropically crops like Citrus, cocoa, coffee, rubber, oil palm, mango, jackfruit, etc. belong to this group. ✓ Such seeds present considerable difficulties in storage. ✓ They require in situ conservation.
- Evaluation
✓ Evaluation refers to screening of germplasm in respect of morphological, genetical, economic, biochemical, physiological, pathological and entomological attributes. ✓ Evaluation requires a team of specialists from the disciplines of plant breeding, physiology, biochemistry, pathology and entomology. ✓ First of all a list of descriptors (characters) for which evaluation has to be done is prepared. ✓ This task is completed by a team of experts from IPGRI, Rome, Italy. The descriptors are ready for various crops. ✓ The evaluation of germplasm is down in three different places, viz., (1) in the field, (2) in green house, and (3) in the laboratory.
- Documentation:
✓ It refers to compilation, analysis, classification storage and dissemination of information. ✓ In plant genetic resources, documentation means dissemination of information about various activities such as collection, evaluation, conservation, storage and retrieval of data. ✓ Now the term documentation is more appropriately known as information system. Documentation is one of the important activities of genetic resources.
b) Wild Germplasm it is used to transfer resistance to biotic and abiotic stresses, wider adaptability and sometimes quality such as fibre strength in cotton.
Organizations associated with germplasm
IPGRI : International Plant Genetic Resources Institute ,Rome ,Italy
NBPGR : National Bureau of Plant Genetic Resources,New Delhi
CENTRES OF DIVERSITY AND GENE BANKS
Gene Sanctuaries
✓ The genetic diversity is sometimes conserved under natural habitat. The areas of great genetic diversity are protected from human interference. ✓ These protected areas in natural habitat are referred to as gene sanctuaries. Gene sanctuary is also known as natural park or biosphere reserve. ✓ Gene sanctuary is generally established in the centre of diversity or microcenter. India has setup its first gene sanctuary in the Garo Hills of Assam for wild relatives of citrus. ✓ Efforts are also being made to setup gene sanctuaries for Banana, Sugarcane, Rice and Mango. In Ethiopia gene sanctuary for conservation of wild relatives of coffee was setup in 1984.
Advantages Gene sanctuary :
- It protects the loss of genetic diversity caused by human intervention.
- It allows natural selection and evolution to operate.
- The risks associated with ex situ conservation are not operative
Disadvantage of Gene sanctuary :
- Entire variability of a crop species can not be conserved.
- Its maintenance and establishment is a difficult task.
- It is a very good method of in situ conservation.
Genetic Erosion :
✓ Genetic erosion refers to loss of genetic diversity between and within populations of the same species over a period of time. or ✓ Gradual reduction in genetic diversity in the populations of a species, due to elimination of various genotypes, is called genetic erosion. ✓ Thus genetic erosion leads to reduction of the genetic base of a species due to human intervension and environmental changes. ✓ There are five main reasons of genetic erosion
- Replacement of land races with improved cultivars : ✓ The main features of modern cultivars are high yield, uniformity, narrow genetic base and narrow adaptability. ✓ On the other hand land races and primitive cultivars have more genetic diversity, broad genetic base, wider adaptability and low yield potential. ✓ (^) Thus replacement of land races with modern cultivars has resulted in reduction in genetic diversity because land races are disappearing.
- Modernization of agriculture : ✓ Clean and modern agriculture, Improved crop management practices has resulted in the elimination of wild and weedy forms of many crops. ✓ These weedy forms enhance the genetic diversity through introgression of genes from crop to weedy forms and weedy forms to crop plants.
✓ A place where germplasm is conserved in the form of seeds is called seed gene banks. Seeds are very convenient for storage because they occupy smaller space than whole plants.
✓ However, seeds of all crops can not be stored at low temperature in the seed banks. The germplasm of only orthodox species (whose seed can be dried to low moisture content without losing variability) can be conserved in the seed banks. In the seed banks, there are three types of conservation, viz., (1) short term, (2) medium term, and (3) long term.
✓ Base collections are conserved for long term (50 years or more) at
- 18 or – 200C. Active collections are stores for medium term (10-15 years) at zero degree Celsius and working collection are stored for short term (3-5 years) at 5-100C.
Advantages of seed gene banks
- Large number of germplasm samples or entire variability can be conserved in a very small space.
- In seed banks, handling of germplasm is easy
- Germplasm is conserved under pathogen and insect free environment
Disadvantages of germplasm conservation in the seed banks:
- Seed of recalcitrant species can not be stored in seed banks
- Failure of power supply may lead to loss of viability and there by loss of germplasm
- It requires periodical evaluation of seed viability. After some time multiplication is essential to get new or fresh seeds for storage.
- Field Gene banks:
✓ Field gene banks also called plant gene banks are areas of land in which germplasm collections of growing plants are assembled. ✓ This is also ex situ conservation of germplasm. Those plant species that have recalcitrant seeds or do not produce seeds readily are conserved in Field gene banks.
✓ In field gene banks, germplasm is maintained in the form of plants as a permanent living collection. ✓ Field gene banks are often established to maintain working collections of living plants for experimental purposes. Field gene banks have been established in many countries for different crops. ✓ Field gene banks in some countries Name of country Crop species for which field gene bank is established
Malaysia Oil palm has been conserved on 500 hectares
Indonesia Earmarked 1000 hectare area for coconut and other perennial crops
Philippines South East Asia germplasm of banana has been conserved
India Global collection of coconut has been conserved in Andman & Nicobar
Field gene banks have some advantages and disadvantages. Advantages :
✓ It provides opportunities for continuous evaluation for various economic characters. ✓ It can be directly utilized in the breeding programme
Disadvantages :
✓ (^) Field gene banks can not cover the entire genetic diversity of a species. It can cover only a fraction of the full range of diversity of a species. ✓ The germplasm in field gene banks is exposed to pathogens and insects and sometimes is damaged by natural disasters such as bushfires, cyclones, floods, etc. ✓ Maintenance of germplasm in the field gene banks is costly affair 3.Meristem gene banks : ✓ Germplasm of asexually propagated species can be conserved in the form of meristems.
✓ The techniques for cryopreservation of plant cells and tissues are being rapidly refined, and some such banks have been established, e.g., for potato in Germany.
6.DNA Gene Banks :
✓ In these banks, DNA segments from the genomes of germplasm accessions are maintained as cosmid clones, phage lysates or pure DNA (the last one being for relatively short periods). ✓ These DNA segments can be evaluated and the desired ones may be used to produce transgenic plants. ✓ This approach is applicable to the conservation of genetic materials of already extinct species since DNA extracted from well preserved herbarium specimens can often be cloned. ✓ However, it is very expensive and highly sophisticated. A world- wide network of DNA banks for threatened / endangered species has been established.
CENTRE OF ORIGIN
NATIONAL & INTERNATIONAL INSTITUTES INVOLVED IN PLANT BREEDING
CENTRAL INSTITUTE FOR CROP IMPROVEMENT
- (^) Indian Agricultural Research Institute (IARI)
- Established in Pusa Campus ,Bihar in :
- Initial named as Imperical Agricultural Research Institute
- Instutute building damageded by Earth quake :
- Institute shifted to Pusa campus ,New Delhi :
- Renamed to Indian Agricultural Research Institute :
- IARI is primary Agricultural Research Institute
- (^) Two yr. Post graduate diploma programme was started in :
- IARI granted the status of Deemed University by the University Grant Commission ,New Delhi :
- NBPGR as a scheme for Plant Introduction in the Botany of these Institute
- Many central Institutes own their origin to research projects initiated in this Institute e,g-SBI ,CTRI ,CPRI ,Induian Lac Research Institute
- Sugarcane Breeding Institute (SBI)
- Established in :
- Location :Coimbatore ,Tamil Nadu
- Taken over by the Madras Govt. in :
- Institute became a part of ICAR in :
- It has 4 stations at :
- Karnal(Haryana)
- Cannanore(Kerala)
- Lucknow(U.P)
- (^) Motihari(Bihar)
- Research on Genetics & Cytogenetics of Sugarcane
- Evolved nearly 2000 varieties of Sugarcane.
- Prefix used in the developed variety :Co
- Germplasm collection :2800 entries
- First Head of the Institute :Dr.C.A.Barber(1912-28)
- Cross between Saccharum officinarum & S.spontaneum initiated by :Dr.C.A.Barber(1912-28)
- After the name of C.A.Barber Indian canes are known as :S.barberi
- Notable achievement :Cross between Sugarcane & Maize ,& Sugarcane & Sorghum
- National Hybridization Garden was est.at Coimbatore ,TN :
- Indian Instiutute of Sugarcane Research (IISR)
- Year of Establishment :
- Location :Dilkusha ,Lucknow ,U.P
- (^) Taken over by ICAR :
- Botany & Breeding section was added for Sugarcane improvement :
- AICRP on Sugarcane present at IISR Institute
