Page 77 - Introduction to Agriculture by: Aqleem Abbas

Introduction to Agriculture Notes prepared by: Aqleem Abbas

Sudden new variations or changes that is inherited. It is variously used to include individual gene
changes and chromosome changes.

Polyploidy

Any organism with more than two sets of basic or monoploid (haploid) no of chromosomes. It is
exact multiple of monoploid.

For example triploid three sets of chromosomes

Tetraploid, and penta ploid. 23,46,69 etc.

Aneuploid or heteroploid
It is not an exact multiple of monoploid.
Hyper…….23 multiple is 46 but here 47 forms.
Hypo………23 multiple is 46 but here 45 forms.
Recombination
The observed new combination of characters different from those shown or exhibite by parents.
Explanation
These process occurs in nature but a plant breeder strive to increase frequency and attempts to
induce the desired changes. The new genotype serves as the basis for selection and further
breeding. The knowledge and control of these basic processes has revolutionized plant breeding
and man has been able to successfully create new and useful varieties. Origin of wheat is good
example. These crops originated in nature is a result of complex hybridizations and polyploidy
over a no of years. But man has been able to resynthesize this plants in only a few years by
controlled crosses and induce doubling of chromosome complement of hybrids. Many species of
brassica and solanum has been resynthesize. Generally autopolyploid are more vigorous than
corresponding diploid and tend to have large leaves, fruits, flowers, seeds etc.
The knowledge that radiation can induce mutations are available and many chemicals also
known which can induce mutations. Triple gene dwarf wheat variety is good example of induce
mutation.

MODES OF REPRODUCTION IN PLANT CROPS

Reproduction is a mean of increasing population as well as maintaining continuity of species.
Before initiating a breeding program a plant breeder should have a good knowledge of plant
reproductive system.
Reproduction in plants can occur by three main ways.
a. Sexual reproduction
b. Asexual reproduction e.g. apomixes
c. Vegetative reproduction or cloning propagation.