BOTANY Higher Secondary Second Year - Textbooks Online

Protoplasmic fusion or somatic hybridization
A hybrid produced from fusion of protoplasts of two different species
is called somatic hybridization. Naked protoplasts are obtained through
dissolution of their cell walls by the macerating enzymes such as pectinase
and cellulase. Fusion of protoplasts from two different varieties can be
enhanced by treatment with the chemical called polyethylene glycol (PEG)
in the presence of high voltage electric current on a suitable medium. By
this method somatic hybrid plants with desirable changes can be obtained.
This method in plant breeding is called protoplasmic fusion. This concept
had been studied by you already in the chapter four.
Heterosis
The superiority of the F 1 hybrid in performance over its parents is called
heterosis or hybrid vigour. Vigour refers to increase in growth, yield,
resistance to diseases, pests and drought. F 1 hybrids of maize show 25%
increase in yield when compared to their own parent crop. Vegetative
propagation is the best suited measure for maintaining hybrid vigour,
since the desired characters are not lost and can persist over a period of
time.
Polyploid breeding
The source for plant breeding is variations in plants.. Heritable and
desirable variations occur in nature by mutation, polyploidy, recombination
and chromosomal aberrations. A diploid plant has two sets of chromosomes
but any organism in which the number of sets of chromosome is doubled
is called a polyploid.
When chromosome number is doubled by itself in the same plant, it
is called autopolyploidy. For example, three sets of chromosomes i.e. a
triploid condition in sugar beats, apples and pear has resulted in the increase
in vigour and fruit size, large root size, large leaves, flower, more seeds
and sugar content in them. Seedless tomato, apple, watermelon and orange
are autopolyploids.
Polyploidy can be induced by the use of colchicine to double the
chromosome number. Allopolyploids are produced by multiplication of
chromosome sets that are initially derived from two different species.
eg. Triticum × Secale gives Triticale.
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