Micropropagation

It refers to artificial propagation of plants vegetatively through the culture of cell or tissue. It is most useful, when normal propagation takes long time or the success in fertilization is very poor as seen in many valuable plants useful in agriculture, horticulture and forestry.

Micropropagation can be done in two ways

Multiple shootlet production

Large number of genetic replicas of rare hybrid or sterile valuable plant can be produced asexually by culturing shoottips. Since propagation is vegetative, the problems of heterogeneity, pollination, divergent inheritance, chromosomal and gene transformations are completely avoided in such methods.

It is greatly useful in large scale cloning of plants in a small space irrespective of season and climate. Commercial success in micropropagation of potato, cardamom, orchids, bananas, chrysanthamun, gerebera, begonia are reported.

Somatic embryogenesis

In this method embryos are generated artificially by somatic cells carrying 2n chromosomes as against embryos normally produced in nature by gametes carrying chromosomes. These embryos are called embryoids. They are grown in large number in a small volume of nutrient medium. Each embryoid can be grown into a separate plant - by transfer of such partially grown plants to fields later.

Production of diseases free plants

Controlling the disease or developing resistant varieties is time consuming and subject to variations in heritability of resistance over generations. But, disease free plants could be grown through the technique of tissue culture in a very short span of time overcoming the seasonal barriers without any risk of heritability. A disease resistant crop is normally selected from a field and selected tissues are subjected to tissue culture techniques to produce large number of disease free plants. Disease free plants of crops like banana are commercially cultivated by tissue culture methods. Many other crops such as potato, sugarcane, sweet potato, strawberry, geranium and cassava are also attempted to be produced by tissue culture methods.

Production of haploids

Haploids are organisms, whose cells contain haploid number of chromosomes - as against normal diploid number of chromosomes. Haploid cells are usually found in gametes of any organism. But when entire plant body contains haploid cells - it offers a great advantage as such plants are comparable to pure lines. Commercial use of haploids in place of pure lines avoid a waiting period - as a pure line can be produced over a span of 6 - 8 generations by repeated selfing.

Tissue culture technique can be used to produce androgenic haploids - which mean production of haploid plants by culturing male gamete (pollen). As each plant has potentiality to produce millions of pollen grains - proper tissue culture methods to produce haploids from each pollen can result into production of large haploid plants.

Androgenic haploids have great importance in breeding programmes - as haploids could be used in one of the following manners.

1) Haploids could be used to achieve great homozygocity in one step - avoiding a long process of evolving a pure line (6 - 8 years) which is known for homozygocity. For this purposes the haploids are subjected to colchicine induced doubling and double homozygous off spring is an excellent homozygous parent for breeding.

2) Haploids could be used for mutation breeding wherein mutant can be expected to exhibit the definite phenotypic characters.

3) In commercial hybrids, the heterosis depends on purity or homozygocity of parents. Tissue culture haploids - later doubled could be a perfect parent in hybrid seed production.