HYBRIDISATION
Defination of hybridisation in biology:
The process of combining different variety of organisms to make a hybrid.
There are two types of hybridisation:
● Interspecific - hybridisation between different species.
● Intraspecific - hybridisation between same species.
Josef Gottlieb Kolrueter, was the first person to study plant hybridization. He represent his first experiment on tobacco in the year 1760. Josef kolrueter concluded that interspecific hybridisation is very rare in nature until humans does not disturb.
The term hybrid is derived from Latinhybrida, used for crosses. By hybridisation process hybrid, can got the specification of both parent. Hybrids are not always intermediates between their parents (such as inblending inheritance), but can show hybrid vigour, often growing larger or taller than parents. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent specied are. Plants hybrid much more faster and better than animals. Pollen grains from flowering plant spread widely with air and reproduce more faster than animals.
Today we are seeing millions of different species of plant and animals in this world, this is the result of hybridisation which are taking place since life came on this earth. For example: A mule is a sterile hybrid of a male donkey and a female horse. Mules are smaller than horses but stronger than donkeys.
Hybridisation in plant
In the hybridisation process two plants with desired character are made to cross and develop seeds. In this process one plant is considered as male plant and another is considered as female plant. The pollen grains from male plant dusted on the stigma of female plant. The fusion of desired male and female gamets resulted in the formation of the hybrid embryo with the characters of both.
Hybridisation process occur in plant through nature by many ways like through insects, when a insect sit on flower of a plant ( genotype AA), the pollen grains stick on the the body of the insect, and again the insect sit on another flower (genotype aa) of different plant then pollen grains transferd to that plant. And then there is formation of embryo (seed) which have genotype Aa. This is the most common process of hybridization in plant by natural process. In plant with autogamous flowers ( flowers which have both part 'stamens' and 'pistils') cross pollination is very rare. Such type of plant is called self pollinated. Example: Rice, Wheat etc.
There are different types of hybridisation process
(a) Intravarietal hybridisation
(b) Intervarietal hybridisation
(c) Intergeneric hybridisation
(d) Interspecific hybridisation
(a) Intravarietal hybridisation: This type of hybridisation done between two plants belonging to the same variety.
(b) Intervarietal hybridisation: This type of hybridisation done between two plants belonging to the different varieties.
In detail:
In this type of hybridization the parents involved are belong to the same species; they may be two strains, varieties or races of the same species. In crop improvement programmes, intervarietal hybridization is the most commonly used. An example would be crossing of two varieties of wheat (T. aestivum), rice (O. Sativa) or some other crop. The intervarietal hybridization categorized in to two simple or complex depending upon the number of parents involved.
Simple Cross:
In this type of cross, two parents are crossed to produce the F1 (embryo). The F1 is self to produce F2 or is used in a back cross programme.
Example: A X BF1 (AX B)
Complex cross:
In this type of cross there are more than two parents are crossed to produce the F1 (embryo) hybrid, which is then used to produce F2 or used in back cross. This type of cross brings quality of different parents in a single hybrid so, it is also called convergent cross.
Example for three parents:
A, B, C (Three Parents)
A X BF1: (A X B) X C = Complex hybrid (AX B) X C
Example for four parents:
(A, B, C, D)
A X B
C X DComplex hybrid (A X B) X (C X D).
(c) Intergeneric hybridisation: Its done between two different genera.
In detail:
This type of hybridization occurs between plants in two different genera in the same family. They are closely related enough that pollination will produce a hybrid, though the seeds of this hybrid are usually sterile. The more distant the relation between the two genera, the greater the difficulty of intergeneric hybridization. Genera that generate intergeneric hybrid are always genetically related members of the same taxonomic Tribe . This type of hybridization represents an opportunity to combine genomes from distinctly different plants and to introgress traits not found in the main genus of interest. Many intergeneric hybrids are infertile.
(d) Interspecific hybridisation: This type os hybridisation done species of same genus.
Benifit of Hybridization
In 1761 Joseph Gottlieb Kölreuter was the first to report on hybrid vigor in interspecific crosses of various species of Nicotiana. He concluded that cross-fertilization was generally beneficial and self-fertilization was not. In 1799 T. A. Knight conjectured that because of widespread existence of cross-pollination in nature, it must be the norm (prohibited).
Charles Darwin concluded after his experiment with maize. He found that there is an increasment in height of plant in which cross-pollination occurred and there is there is no increasment even decreasement in height of plant in which self-pollination is occurred. After observation of this experiment Darwin write a book name "Nature tells us" in the year 1862.
Again in the year 1800, William J Beal done an experiment and he found that, some hybrids yielded 50 percent more than the mean of their parents.
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