BOTANY Higher Secondary Second Year - Textbooks Online

The haploid individual plant will have only one set of chromosome.
Through the technique of anther and ovary culture, haploid plants can be
modified to diploid ones by doubling their chromosomes. Variations that
are brought forth through plant tissue culture are called somoclonal
variation. eg. disease resistant potato and rust resistant wheat. Varieties
of short duration sugarcanes are produced by polyploid breeding.
Mutation breeding
Radiation induces mutation to develop new variety of crops. Now
with newer and more powerful sources of radiations (UV shortwave, Xray,
Alpha, Beta, Gamma waves) and many chemicals (mutagens) eg.
Caesium, ethyl methane sulfonate, nitromethyl urea), we can increase the
rates of mutation eg. Triple gene dwarf wheat with increase in yield and
height. Atomita 2-rice with saline tolerance and pest resistance, groundnuts
with thick shells are products of breeding methods through induced
mutation.
Breeding for disease resistance
.
Many crop plants suffer from several diseases caused by pathogens
such as bacteria, fungi, viruses, nematodes, protozoa and mycoplasma.
In vegetatively propagated plants like potato, cassava, sugarcane and dahlia,
viral pathogens are transmitted through their roots, tubers, bulbs and
rhizomes. Disease free plants are obtained by shoot apical meristem culture
technique. Plants raised through tissue culture are free from pathogens,
which are widely cultivated.
Whenever, a trait that shows disease resistance in a plant is observed,
the best way to transfer that trait to other useful crop is by the method of
backcross. Repeated back crosses are attempted with the parent crop with
more desirable characters and such a crop is known as recurrent parent.
For example, A is a non-recurrent parent and B* is a recurrent parent
with desirable trait.
A x B* → C x B* → D x B* → E x B* →
F x B*
↓ ↓ ↓ ↓ ↓
C D E F G*
* desirable disease resistance with disease resistance
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