Tissue Culture

As traditional breeding methods proved too slow to keep pace with the demand for improved crops, a new technology — tissue culture — was developed to make crop improvement faster and more efficient.

Totipotency and micropropagation

During the 1950s, scientists discovered that a whole plant could be regenerated from an explant — any small part of a plant removed and grown in a test tube under sterile conditions in a special nutrient medium. This ability of a single cell or explant to give rise to an entire plant is called totipotency. For this to work, the nutrient medium must supply a carbon source such as sucrose, along with inorganic salts, vitamins, amino acids and growth regulators such as auxins and cytokinins.

This technique makes it possible to produce very large numbers of plants in a short time, a process called micro-propagation. Every plant produced this way is genetically identical to the original plant it was grown from — such genetically identical individuals are called somaclones. Important food crops such as tomato, banana and apple are already propagated commercially by this method.

Producing virus-free plants

Tissue culture also allows the recovery of healthy plants from ones that are infected with a virus. Even in an infected plant, the meristem (both apical and axillary) remains free of virus. By removing the meristem and growing it in vitro, scientists can obtain virus-free plants — a technique that has been used successfully to culture the meristems of banana, sugarcane and potato.

Somatic hybridisation

Scientists have gone a step further by isolating single cells from plants and, after digesting away their cell walls, obtaining naked protoplasts (cells surrounded only by their plasma membrane). Protoplasts isolated from two different plant varieties — each carrying a desirable trait — can be fused to form a hybrid protoplast, which can then be grown into a new plant. Such hybrids are called somatic hybrids, and the overall process is known as somatic hybridisation. …