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
- Allium sativum (Liliaceae) Garlic mosaic virus
- Brassica Oleracea (Brassicaceae) Cabbage black ringspot virus, Turnip mosiac virus, cauliflower mosiac virus
- Chrysanthamum sp. (Asteraceae) Chlorotic mottle, Green Flower, stunt vein mottle, virus B.
- Dahlia Sp. (Asteraceae) Dahlia mosaic virus, Tomato Aspermy, vein mottle, virus B.
- Glycine max (Fabaceae) Soyabean mosaic virus. Impomoea batatas Feathery mottle, Hanmon Mosiac, (Convolvulaceae) ` Rugosa mosaic
- Lilium Sp. (Liliaceae) Cucumber mosia virus
- Monihot Sp. (Euphorbiaceae) African cassava mosiac
- Musa sp. (Musaceae) Cucumber mosiac virus
- Nicotiana tobacum (solanaceae) tobacco mosaic virus
- 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.