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Monday, March 29, 2010

Plant Breeding and Hybridisation

Monday, March 29, 2010
PLANT BREEDING
PLANT BREEDING:
Plant breeding is a process of developing improved varieties of plants with desirable characters from the existing ones is called plant breeding.It can also be defined as the improvement of plants by the application of genetic principles.
METHODS USED IN PLANT BREEDING:
1)PLANT INTRODUCTION:
It is a process of introducing new plants with desirable characters from their area of origin to a new area is called plant introduction.this process is very fast and easy method of breeding.
If the plant if brought from foreign country than it is called exotic plant and if it is from the same country then it is called as indigenous plant.
Adjustment of plants to new or changed environment is called acclimatisation.
Plant introduction are usually done by cuttings or seeds.
2)SELECTION:
it is the oldest method of breeding process.It involves picking up of better ones from the entire crop plants.
TYPES OF SELECTION:
a)MASS SELECTION:
It is the simplest method followed by the farmers to improve mainly local varieties of crops.Before harvesting the crops,best looking and healthy plants are selected from the mass.seeds of these plants are collected and sowed them to raise new generation.Mass selection is based on external character.
b)PURELINE SELECTION:
A pureline is progeny obtained from a single individual by self fertilisation.A group of plants obtained from a single self fertilized homologous plant is called pureline.
It involves a desirable homologous individual from the mixed population and multiplying the same.Pureline selection is the only method of improvement of local varieties of self pollinated crops.The progeny of pureline selection are similar in phenotypical and genotypical character.
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 vegatively propagated plant.

3)HYBRIDISATION:
The process of crossing two or more plants together to get offsprings of new desirable characters as a result of genetic recombination is called Hybridisation.
TYPES OF HYBRIDISATION:
a)INTRASPECIFIC HYBRIDISATION;
Crosses are made between two individuals of same species.This crosses are done to improve self pollinated crops producing homozygosity or pure offspring.
b)INTERSPECIFIC HYBRIDISATION:
Crosses are made between individual of different varieties of the same species.This crosses are made to improve self pollinated and certain cross pollinated crops.
c)INTRAGENERIC HYBRIDISATION:
Crosses are made between two individuals of different species belonging to same genera.it is used to produce resistance varieties from diseases ,frost or drought.
d)INTERGENERIC HYBRIDISATION:
Crosses are made between two individuals of different genera belonging to same fanily.It produces resistance varieties as well as desirable combination of all characters.
Eg:Brassica X Raphanus=Raphanusbrassica

TECHNIQUES FOR HYBRIDISATION:
It is necessary for the breeder to have following information:
a)Whether plants are self or cross pollinated.
b)Whether plants are monoecious or dioecious.
c)Whether the flowers are unisexual or Bisexual.
d)time of Anthesis.

PROCESS OF HYBRIDISATION:
a)SELECTION OF PARENTS:
Male and female parents,with desirable characters are selected from the avaible materials.Both the parents should mature at the same time.
b)EMASCULATION:
Removal of anthers from bisexual flowers before they dehisces or shed their pollen is known as emasculation.It is done in order to prevent self fertilisation.Emasculation is not necessary in the parents are monoecious.
c)BAGGING:
After emasculation,flower buds are kept enclose in bags made up of cloths,plastic or polythene etc.It is done to prevent pollination through unknown pollen.
d)CROSSING:
it is an artificial pollination.Pollens are collected from the desirable male flowers.These collected pollens are then dusted on the stigmas of pistils.After crossing the female flowers are bagged again.
e)LABELLING:
The female parents are then labelled properly.The labelling should bear the following information.
i)Serial number
ii)Details of male parents and female parents.
iii)Date of emasculation and crossing
f)HARVESTING:
At the end of the season,the fruits and seeds of each cross are separately collected.They are dried and preserved and then sowed to raise the F1 generation.

HYBRID VIGOUR:
The superiority of offsprings over their parents is known as hybrid vigour or heterosis.

4)MUTATION BREEDING;
Mutation is define as a sudden change in hereditary of an organism.They may be due to changes in chromosome number(Polyploidy),changes in the structure of chromosome(chromosomal abbrevation) or changes in molecular level of DNA(gene mutation).
Mutation may occur naturally or artificially,produced by exposing organism to mutagenic agents like X-rays,Gamma rays etc.
5)POLYPLOIDY BREEDING:
Polyploidy breeding involves use of polyploidy in crops improvement.In general the odd numbered polyploidy 3x,5x etc are sterile while even numbered polyploid are fertile.There are two main categories of polyploidy.
a)Autopolyploids(multiples of same genomes)
b)Allopolyploids(multiples of different genome)

APPLICATION OF PLANT BREEDING:
The main objective of plant breeding is to produce improved variety of plants with desirable character from existing ones based on principles of genetics.Some of the application of plant breeding are listed below:
a)INCREASE IN YIELD:
Nowadays,plants breeders have become successful in producing improved varieties of crops that can produce higher yields of cereals,fibres,oil,sugar etc.
b)IMROVED QUALITY:
Through plant breeding,good quality of plant with desirable character are produced.
c)RESISTANCE OF DISEASE:
Every year thousands of plants get affected by several diseases.But plant breeding has enabled to produce disease resistance varieties plants.
d)PRODUCTION OOF VARIETIES SUITED TO PARTICULAR CLIMATE AND SOILS:
Plant breeders are able to develop hardy varieties which can withstand drought and frost.
e)CHANGE IN DURATION OF MATURITY:
Plant breeding has shortened the duration of crop maturation as result of which more types of crops are produced in same year.
f)RESISTANCE TO LODGING:
Plants breeder are producing plants with between lodging.

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