Page 77 - Introduction to Agriculture by: Aqleem Abbas
P. 77

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.
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