→ As traditional breeding techniques failed to keep pace with demand and to provide sufficiently fast and efficient systems for crop improvement, another technology called tissue culture got developed.
→ It was learnt by scientists, during 1950s, that whole plants could be regenerated from explants, i.e., any part of a plant taken out and grown in a test tube, under sterile conditions in special nutrient media.
→ This capacity to generate a whole plant from any cell/explant is called totipotency.
→ It is important to stress here that the nutrient medium must provide a carbon source such as sucrose and also inorganic salts, vitamins, amino acids and growth regulators like auxins, cytokinins etc.
→ By application of these methods it is possible to achieve propagation of a large number of plants in very short durations.
→ This called micro-propagation.
→ Each of these plants will be genetically identical to the original plant from which they were grown, i.e., they are somaclones.
→ Many important food plants like tomato, banana, apple, etc., have been produced on commercial scale using this method. Try to visit a tissue culture laboratory with your teacher to better understand and appreciate the process.
→ Another important application of the method is the recovery of healthy pltnts from diseased plants.
→ Even if the plant is infected with a virus, the meristem (apical and axillary) is free of virus.
→ Hence, one can remove the meristem and grow it in vitro to obtain virus-free plants. Scientists have succeeded in culturing meristems of banana. Sugarcane, potato. etc.
Somatic hybridisation :
→ Scientists have even isolated single cells from plants and after digesting their cell walls have been able to isolate naked protoplasts (surrounded by plasm membranes).
→ Isolated protoplasts from two different varieties of plants each having a desirable character - can be fused to get hybrid protoplasts, which can be further grown to form a new plant. These hybrides are called somatic hybrids while the process is called somatic hybridisation.
→ When a protoplast of tomato is fused with that potato, and then they are grown to form new hybrid plants combining tomato and potato characteristics.
→ Well this has been achieved - resulting in formation of pomato; unfortunately this plant did not have all the desired combination of characteristics for its commercial utilisation.