During the last decade, tremendous progress has been made in the area of plant cell, tissue & organ culture. In vitro techniques constitute an important component of biotechnology, and have the potential not only to improve the existing cultivars, but also for the synthesis of novel plants & early release of high - yielding plants resistant to various diseases, pests, stresses & temperature. Green revolution of recent years has been the result of efforts that led to the improvement & better selection of species of agronomic interest. Some specialists feel that biotechnology is the second phase of green revolution, studies are already in progress to obtain crop plants having higher photosynthetic efficiency, improved fixation of atmospheric nitrogen, increased nutritional quality & greater tolerance of salinity, alkalinity, acidity, deficiency of nutrients & stresses. Wide hybridization through embryo & ovule culture both at the interspecific & intergeneric levels have been achieved in a number of crops through the culture of the hybrid ovules & embryos. In vitro fertilization techniques have also been employed to overcome incompatibilty. Haploids produced through anther culture & their diplodization have resulted in the release of varieties in crops such as wheat & rice.

Biotechnology -

The term biotechnology is composed of two words - bio (Greek-bios-means life) and technology (Greek technologia - means systematic treatment). In other words, it is the science of applied biological processes. Accordingly to the oxford Dictionary, technology is the "Scientific study of the practical or industrial arts".

Spinks (1980) defined biotechnology as, "the application of biological organisms, systems or processes to manufacturing & service industries".

European Federation of Biotechnology (1981) defined biotechnology as, "the integrated use of biochemistry, microbiology & engineering sciences in order to achieve technological (industrial)application of the capabilities of micro-organisms, cultured tissue cells & parts thereof".

In the report Biotechnology : A Development plan for Canada (1981) biotechnology is defined as "the utilization of a biological process, be it microbial, plant or animal cells, and their constituents, to provide goods & services".

Some of the areas where biotechnology has played a significant role are detailed below.

1. Production of pathogen - free plants.

Plants traditionally being vegetatively propogated are systemically infected with viruses & other pathogens which greatly reduce yield & also Q uality of the marketed commodity. Virus diseases like potato leaf roll virus (PLRV) or potato virus Y (PVY) for example, can cause upto 95 % reductions in the tuber yield of potato crops. Increase in yield upto 300% (Averaging 30%) has been reported following replacement of virus - infected stock with specific pathogen free plants.

since majority of viruses infect plants in a systemic manner their eliminaion may be achieved through meristem tip culture.

- Plant species for which virus - free plants have been obtained.

species virus eliminated

1. Allium sativum (Liliaceae) Garlic mosaic virus

2. Brassica Oleracea (Brassicaceae) Cabbage black ringspot virus, Turnip

mosiac virus, cauliflower mosiac virus

3. Chrysanthamum sp. (Asteraceae) Chlorotic mottle, Green Flower, stunt

vein mottle, virus B.

4. Dahlia Sp. (Asteraceae) Dahlia mosaic virus, Tomato Aspermy,

vein mottle, virus B.

5. Glycine max (Fabaceae) Soyabean mosaic virus

. Impomoea batatas Feathery mottle, Hanmon Mosiac,

(Convolvulaceae) ` Rugosa mosaic

7. Lilium Sp. (Liliaceae) Cucumber mosia virus

8. Monihot Sp. (Euphorbiaceae) African cassava mosiac

9. Musa sp. (Musaceae) Cucumber mosiac virus

10. Nicotiana tobacum (solanaceae) tobacco mosaic virus

11. solanum tuberosum(solanaceae) potato virus

Although the apical meristems are often free of viruses, this cannot be regarded as a phenomenon of u niversal occurence. The sucess of meristem tip culture depends upon several factors. One of the most important factors is the relative distribution of viruses in the growing tip of donor plants. There are some viruses which invade the growing tip viz, TMV, potato virus X, cucumber mosaic virus. In such cases virus free plants are obtained by combining meristem - tip culture with high temperature treatments.

2. Production of Disease Resistant Plants.

This is one of the most useful applications of tissue culture in crop improvement. In potato, somaclones have been screened for both late & early blight resistance. In maize, somaclonal variation has induced resistance to race T of southern corn leaf blighrt. In sugarcane, resistance to diseases like fiji & downy mildew have been recovered. In lucerne, selection of cell lines & plants resistant to the toxin of Fusarium oxysporium has been accomplished.

3. Improvement of nutritional quality

One of the major sources of protein for human & animal commnsumption is constituted by the proteins contained in seeds of many plant species. The cereals & legumes which are major sources of storage seed proteins, contain limited amount of certain amino acids which are essential for human beings. Majority of these cereals are deficient in lysine whereas legumes are deficient in sulpher amino acids. A wide range of approaches have been employed for improving nutritional quality of various crop plants. Important among them are selecting cell lines resistant to amino acid or their anologues of lysine, tryptophan, proline & phenylalanine. Isolation of variants over producing specific amino acids in culture has been successful, but expression in the whole plant & especially in the seed has not yet reached the level required to make an impact on protein quality.

4. selection for salt & draught tolerance

Continued efforts to increase intensity of cropping for increasing production

from limited land resource by extending irrigation facilities have resulted in the gradual build-up of salt concentrations in the soil. This has resulted in loss of productivity on such soils.

Salt tolerant lines have been produced in crop plants such as tobacco, tomato, cereals. Salt tolerance has been incorporated into rice lines with improved plant type. Some of the improved rice cultivars viz., IR 42, IR 43 & IR 52 are salt tolerant.

Development of cultivars tolerant draught can contribute significantly in agriculture economy. Tolerance to draught is a polygenic trait & involves highly complex osmo-regulatory functions. In tissue cultures, simulated draught conditions have been achieved thro'incorporation of non-penetrating osmotic solutes such as PEG (polyethylene glycol) and dextrans in the media.

5. Production of Genetically variable plants.

The success of any crop improvement programme depends on the usable genetic variability in the base population cells in culture offer an excellent systems for inducing variations & regenerating pure mutant types. Genetic variation can be an option to lessen our reliance on cost intensive germ - plasm collection & conservation programmes. Variant producing capacity of cell culture can be augmented to a great extent by employing physical & chemical mutagens. Somaclonal variation has been extensively exploited for the improvement of a sexually propogated crops viz., potato, sugarcane. From cell cultures, some superior cultivars have already been poroduced in sugarcane which are high yielding, drought resistant & temperature tolerant.

6. Biofertilization

Molecular nitrogen in the atmosphere is converted into Biologically converted forms by nitrogen fixing micro-organisms e.g. Rhizobium. The most sophasticated approach to biofertilization is to create plants that possess the genetic capacity for nitrogen fixation. Attemps are being made to transfer genes for nitrogen fixation (hifgenes) from bacteria to plants.

7. Rapid clonal propagation

Tissue culture has found its best commercial application in production of cloned plants at a very high rate as compared to conventional methods. It is important specially for initially building up of propagation stock of elite clones or individual plants which are otherwise slow to multiply. A number of agriculturally important plants have been clonally multiplied.

8. Genmplasm storage

The primitive cultivars & wild relatives of crop plants constitute a pool of genetic diversity which is invaluable for further breeding programmes. There are over 20,000 plant spcies which are rare or threatened with degradation of their neutral habitats. The most economical form of storing germ plasm for seed propagated species is seeds. However, there are certain limitations of this method. Therefore, various methods of invitro storage of germplasm ar e thus of great practical significance for long term storage of germplasm. Presently, there are two approaches to invitro germ plasm storage. Slow growth technique & cryopreservation.

9. Biological control of Agricultural pests

Insects consume nearly one-third of human food supplies on earrth. One of the major goals of biotechnology is to develop target specific biological pesticedes that will kill some specific pest but will not harm other species. Several insect-specific pathogens, developed through biotechnological processes, are being produced commercially for their use as microbial pestices. Bacillus thuringienis inocula have been used as bio-insecticides. Toxin produced by the bactenium kills the gypsy moth. The prevention of crown gall disease formation is achieved by spraying young plants or seeds avirulent species Agrobacterium radiobactor var, radiobactor. Microbial insecticides have a number of advantages over traditional chemical insecticides:

a) they are specific for a small number of species of insects & do not kill plants, animals & beneficial insects.

b) they are cheaper than organic pesticides and

c) they do not leave any residue effect.

10. Selection for Herbicide Resistance

Herbicides are used to control weeds in agricultural fields.

Tissue culture techniques offer several advantages in developing herbicide - resistance plants:

1. The techniques for selection are relatively rapid;

2. Small volumes of cells represent the genetic potential of hectares of fields.

3. Metabolic studies are facilitated by uniform & sterile conditions &3

4. Possible new types of resistance not found in nature may be obtained from plant cell cultures.

Attempts to produce herbicide tolerance using somaclonal variation & invitro selection have already been made.