Introduction to Bio-technology
Introduction to Bio-technologyBiotechnology is a new discipline of science in which the latest technology has been applied to biological organisms for the welfare of society. It is the application ...
PLANT BREEDING 02 ( METHODS )
Methods used in crop improvement or plant breeding are:
- Plant introduction and Accclimatization
- Selection
- Polyploid breeding
- Mutation breeding
- Hybridization
1.Plant introduction and Accclimatization
It is the process of introducing plants with specific characters from their area of origin to a new area where it was not grown before.
This is one of the simplest methods ofdevelopment of improved crop variety.The adaptation of introduced plant new locality is called as Acclimatisation. Plant introduction is of two types:
- IC (Indegenous collection): When introduction is made from the same country.
- EC (Exotic collection): When introduction is made from foreign country
2. Selection:
Selection preserves the favorable variations and eliminates the undesirable variations. Selection is of three types:
a. Mass selection
Picking up seeds of a large number of phenotypically superior plants and sowing them next season in a mass without any progeny testing.
The differential reproduction of only those plants where good characters have been brought in homozygous state through self breeding over few generations.The method is useful for bringing about the maximum and permanent improvement in desired traits.Pure line selection takes lot of time and is useless in case of cross pollinated plants.
c. Clonal Selection:
- A clone is defined as a progeny of a single plant obtained by vegetative propagation.
- The clonal selection is concerned with the selection and propagation of best individual of clones from mixed population of vegetative propagated plant. Clonal selection is equally useful in maintaining superiority of heterozygous, heteroploid or oddploid individual.
- This, method of selection gives instant result and is also a stable selection method.
- Germplasm collection & conservation: Germplasm is the sum total of all the alleles of genes present in various varieties of a crop plant, its related species and wild relatives.
Recalcitrant seeds: They are kept at room temperature under partially humid aerobic conditions for shorter duration. Eg Tea, Coconut, Jackfruit, coca.
3. Polyploid Breeding
- Polyploid is an individual having more than diploid or more than two sets of chromosomes.
- Many of modern day crops such as wheat, rice, sugarcane, cotton are natural polyploids. It is induced artificially by colchicine (spindle poison) and granosan.
i. Autopolyploidy:
- It is the increase in number of the same genome, e.g., AAA,BBBB
- Failure of meiosis during formation of gametes (or spores) forms diploid egg or diploid sperm.
- Fusion of diploid gamete with diploid one forms tetraploid individual, while fusion of diploid gamete with haploid one forms triploid individual.
- Fusion of a normal egg with two sperms also yields autotriploid plants.
ii. Allopolyploidy
- It is also interspecific polyploidy because increase in number of genomes or chromosome sets is due to pooling from individuals of two or more species caused by hybridisation followed by chromosome doubling. e.g.. AABB, AABBC.
- The most common types are allotetraploids or amphidiploids
- Some common examples are Durum wheat.
- It is pooling of chromosome sets from two species, one with diploid and the other with more than diploid states, e.g. Helianthus tuberosum.
- It is possible to induce mutations artificially through use of chemical or radiations (like gamma radiations).
- Incorporation of useful mutations in developing improved varieties is called mutation breeding.
