BOTANY Higher Secondary Second Year - Textbooks Online

Clonal selection
Crops like sugarcane, potato, tea, banana and certain species of grasses
are asexually propagated and produce very poor seeds. Based on their
phenotypic appearance, the method of clonal selection is employed to
select improved variety from a mixed population (clones). Selected plants
are multiplied through vegetative propagation to give rise to a clone. The
genotype of a clone remains unchanged for a long period of time.
Introduction
India has several varieties of crops such as maize, tobacco, tomato,
potato and brinjal which were introduced from countries such as America,
China and Australia. Introduced varieties sometimes do not get adjusted
easily with our local environment. It takes some time for these introduced
crops to settle. Sometimes, it is essential to select suitable and desirable
variety from the introduced plants. For example, a mung Phaseolus mungo
variety was introduced from China but was not giving good yield and
produced dull coloured seeds. From amongst the introduced mung crop, a
plant suddenly produced large and bright coloured seeds. This aspect may
be due to sudden mutation. This variant plant was selected and further
subjected to inter or intra specific crosses with our native crop. In this
way, new varieties were produced and released as newly developed mung
variety. Such a mung No.1 variety is now being cultivated in Punjab.
Hybridization
Hybridization is a method in plant breeding to improve the native
crops by obtaining diverse genotypes that can be used as a source material
for collection of crop with desirable characters and genes obtained from
many parts of the world. It involves crossing of two varieties or species
or genera having desirable genes and breeding them together of the desirable
traits into one progeny, which is called the hybrid. Hybrids are the products
of first generation obtained by crossing genetically unrelated parents.
When two individuals of the same species are crossed, it is called
inbreeding or selfing or self-pollination. This results in the increase of
homozygosity. Particularly homozygous recessive alleles develop loss of
vigor in plants. By careful observation of morphological features, we can
remove these deleterious and harmful alleles by selection.
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