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How to improve crops or plants

January 05, 2014  by: Reena  Points: 12   Category: Others  Earning $0.30   Views: 793

Plant improvement or crop improvement is a method of combining of desired characters from different plants in a single plant and then multiplying it.

         

The technique of plant improvement is by plant breeding to get better yield, to confer resistance to pests, diseases, etc.....

Techniques used in plant improvement are:-
1)Selection:
It is a method in which plants with desirable characteristics are selected and planted year after year. Most of the present day crops are results of such continuous selection over centuries from their wild type ancestors. It is the oldest method of plant improvement.

2)Hybridization:
It is a process of crossing plants having different desirable characteristics, belonging to two different varieties, species or genera to produce hybrids. The superiority of the hybrid over either parents in one or more traits is called hybrid vigour or heterosis.

3)Polyploid breeding:
Polyploidy is a condition is which an organism has more than two sets of chromosomes in their somatic cells. Polyploidy is induced by using a drug called colchicine. Polyploids have a higher hybrid vigour. Many cultivated garden plants and crop plants are polyploids.

4)Mutation breeding:
Mutation is a sudden heritable change in the genetic make up or genes of an individual. Mutations can be induced artificially by treatment with agents called mutagens. Mutations may be induced in seeds, seedlings or young buds.

5)Protoplast fusion:
The plant cell without a cell wall is called protoplast. Cell walls of the cells of two different plants with desirable qualities are removed by treatment with appropriate enzymes. The protoplasts of the two cells are fused to get a single protoplast containing the nuclei of the two cells. This is called heterokaryon. Then, it is cultured in the laboratory to get callus and then many new plants.

6)Tissue culture:
In tissue culture an excised tissue or embryo or a shoot bud may develop into a whole plant. Pollinated ovaries have also been grown to mature fruits. Nevertheless, portions of organs or tissues generally give rise to an unorganized mass of cells called callus.


The following are the benefits of tissue culture in crop improvement:-
a)Micropropagation,

b)Production of disease free plant,

c)Androgenic haploids and their use in breeding,

d)Embryo rescue for successful hybridization,

e)Induction and selection of mutants,

f)Protoplast technology.


GENETIC ENGINEERING:
The objective of genetic engineering or recombinant DNA technology is to introduce one or more genes into an organism that normally does not possess them. This requires isolation of the fragment of DNA corresponding to a desirable character, hooking it to a vector and transferring it to a cell. In spite of the severe limitations, genetic engineering offers immense possibilities, for improving crops that were unthinkable before.


IMPROVEMENT OF RICE:
In the early 1970s an epidemic called grass stunt virus destroyed more than 1,60,000 hectares of rice in Asia. A single sample of wild rice Oryza nivara from Central India was found to be the only source of resistance to the grass stunt virus.

Using 13 rice varieties from 6 countries and the wild Oryza nivara, plant breeders of Indian Rice Research Institute led by Dr. Gurudev S. Khush developed the cultivator IR 36. It is the most widely grown rice variety in the world and occupies over 10 million tonnes of rice each year on a global scale. It is early maturing and is high yielding. Its grains have good milling qualities. It resists many of the major rice pests and diseases and can be grown on a variety of soils. After a decade of occupying vast areas of Asia, IR 36 may become prone to newly appearing diseases and pests. In spite of its likely down fall in future, IR 36 has contributed enormously to feeding Asia's population.


IMPROVEMENT OF WHEAT:
As early as 10,000 to 15,000 B.C. the primitive wild wheat Tritium boeoticum had been grown in the Near East. Its domesticated counterpart is called T.monococcum. Sometimes in its history, T. monococcum was fertilized by a wild goat grass (Triticum spettodes). T.spettoides also has 14 chromosomes but it is compatible with T.monococcum. Their hybrid offsprings are generally sterile. At some time in the past polyploidy occured and a tetraploid with 28 chromosomes emerged. This is known as Triticum turgidum and is commonly called as Emmer wheat. This Emmer hybrid is crossed with another wild grass Aegilops squarrosa. The resulting hybrid offspring with three sets of chromosomes was sterile. However some time during evolution these sterile hybrids doubled to produce the hexaploid wheat with 42 chromosomes. This hexaploid wheat is the bread wheat used world wide.

The most remarkable hybridization is between wheat and rye. This cross was done to combine palatability of wheat and hardness of rye. The outcome was fertile allotetraploid Triticale with 42 chromosomes. This hybrid is the first new man made plant to join the rank of cereals, which have a long evolutionary history. Triticale is now grown all over the world especially U.S.S.R.




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