Which of the following combination of hormones will promote differentiation of shoot as well as root in tissue culture?

The correct option is Auxin and cytokinin.

In plant tissue culture, the differentiation of callus into shoot and root organs (a process known as organogenesis) is primarily controlled by the ratio of two classes of plant hormones: auxins and cytokinins.
This classic plant hormone interaction was first demonstrated by Skoog and Miller in 1957.

Here is a step-by-step breakdown of how these hormones function to promote differentiation in tissue culture:

1. Role of Auxins:
Auxins, such as indole-3-acetic acid (IAA) or naphthaleneacetic acid (NAA), are primarily responsible for promoting cell division and root initiation (rhizogenesis).
When the culture medium has a relatively high auxin-to-cytokinin ratio, root development is favored.

2. Role of Cytokinins:
Cytokinins, such as kinetin or zeatin, promote cell division and shoot initiation (caulogenesis).
When the culture medium has a relatively high cytokinin-to-auxin ratio, shoot development is favored.

3. Balance of Both Hormones:
When both auxin and cytokinin are present in a balanced ratio, they stimulate the proliferation of unorganized cells to form callus.
By sequentially adjusting the relative concentrations of these two hormones in the tissue culture medium, researchers can promote the differentiation of both shoots and roots from the same tissue sample, eventually regenerating a complete plantlet.

Therefore, the combination of auxin and cytokinin is essential for promoting the differentiation of both shoot and root in tissue culture.