Plant Tissue Culture

Traditionally, farmers breed crops over many generations to produce desired qualities, such as higher yields, larger seeds, sweeter fruit, and greater disease resistance. New crop varieties can be created by grafting or cross-pollinating the parent plants. However, these methods are time-consuming and non-specific, with a high chance of eliminating desired traits. 

Alternatively, the use of in vitro techniques known as plant tissue culture can rapidly produce large numbers of plant clones with desired qualities.

This technique relies on ‘totipotency’, which means that a part of a plant can give rise to an entire plant when provided with the appropriate growth regulators and environment. 

Depending on the source of the plant part, or explant, tissue culture techniques can be distinguished into several types.

For example, in callus culture, the tissue explants placed on growth medium undergo rapid cell division and form a mass of undifferentiated cells called a callus.

Plant hormones, such as auxins and cytokinins, regulate several aspects of plant growth and help the callus differentiate into different plant parts. Shoots can be induced from a callus with a high concentration of cytokinins relative to auxins, while roots can be formed when the ratio is reversed. At an equal hormone concentration, both root and shoot form to regenerate the young plant. 

Viruses present a major concern in agriculture because they can cause serious plant diseases. Meristem culture is particularly useful for establishing virus-free plants. This method relies on the rapidly dividing shoot tip as the explant of choice. Such shoot tips are generally free of viruses. 

Plant tissue culture not only enables the cloning of desirable plants, but also facilitates genetic modification. One kind of modification involves introducing beneficial genes that might enhance the health, size, or overall yield of the plant. Such modifications are inherited by subsequent generations and produce the desirable traits without the need of additional tissue culture.

For example, genetically modified, or GM, corn with an herbicide tolerance gene has been widely adopted by farmers in the US. This modification allows crops to be sprayed with herbicide, killing competitor weeds and leaving the crop unaffected.