Auxin hormone is used for the initiation of growth of root as it has the ability for the division of cells and elongation thereby helps in the growth of roots in tissue culture.

The hormone responsible for the growth of the root in micropropagation is auxin.

Explanation:
Micropropagation is a technique used to produce large numbers of genetically identical plants from a small piece of plant tissue. The process involves the growth of plant cells or tissues in a nutrient-rich culture medium under controlled laboratory conditions.

Role of Auxin:
Auxin is a type of plant hormone that plays a crucial role in various aspects of plant growth and development, including root formation. In the context of micropropagation, auxin is used to stimulate root growth from the explant (the small piece of plant tissue used for propagation).

Root Formation:
When a plant tissue is cultured in a nutrient-rich medium supplemented with auxin, it promotes the formation of roots. Auxin stimulates cell elongation and division, leading to the development of a root primordium. The primordium then differentiates into a root, which grows and elongates in response to the presence of auxin.

Selection of Auxin:
Different types of auxins can be used for root induction in micropropagation, such as indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA). These auxins are commonly added to the culture medium in varying concentrations, depending on the plant species and the specific requirements for root development.

Other Hormones:
While auxin is primarily responsible for root growth in micropropagation, other hormones also play roles in the overall process. For example, cytokinins are often used in combination with auxin to promote cell division and shoot formation. Gibberellins may also be added to enhance shoot elongation. However, it is the presence of auxin that is critical for root initiation and development.

In conclusion, auxin is the hormone responsible for the growth of the root in micropropagation. It stimulates root formation from the explant and plays a crucial role in the overall success of the micropropagation process.