Establishment, Multiplication and Rooting Media Explained
Plant tissue culture is rarely performed on one medium from beginning to end. Instead, cultures often move through several stages, each with a different biological goal.
Three of the most important are establishment, multiplication and rooting. Understanding these stages makes tissue culture much easier to manage.
Stage 1: Establishment
Establishment begins when the original explant is introduced into sterile culture.
At this point, the primary goals are simple:
- keep the tissue alive
- obtain a contamination-free culture
- encourage stable growth
- allow the explant to recover from sterilization
Fresh explants have often experienced considerable stress. Leaves may have been removed, tissue has been cut, and the plant has undergone chemical surface sterilization. For this reason, establishment is not necessarily the time to maximize shoot multiplication. A successful establishment culture is simply one that remains clean and begins producing healthy new growth.
Stage 2: Multiplication
Once a culture is stable, the goal changes. Instead of maintaining one shoot, the grower wants to produce several. Multiplication media often contain a stronger cytokinin influence. Cytokinins encourage existing buds to activate and can promote the development of additional shoots. After enough shoots develop, the culture can be divided and transferred to fresh multiplication medium. This process is called subculturing. Repeated subculture can turn one successful explant into many individual plantlets.
When should cultures be subcultured?
Cultures should not remain indefinitely on the same medium.
Over time:
- nutrients are consumed
- sugar becomes depleted
- agar may dry
- waste products accumulate
- PGR exposure continues
The ideal interval depends on the species and growth rate. Rather than following the calendar alone, observe the plants. Healthy actively growing shoots are generally better candidates for subculture than weak or stressed tissue.
Stage 3: Rooting
A shoot produced during multiplication is not automatically ready to leave tissue culture. It usually needs a functional root system. During rooting, the hormone balance is changed to encourage root initiation and elongation. Auxins such as IBA are frequently used for this purpose. The goal is no longer to create as many shoots as possible. Instead, the goal is to produce a strong individual plantlet capable of surviving outside the culture vessel.
Why not use one medium for everything?
A medium that produces excellent multiplication may inhibit rooting. A medium optimized for rooting may produce very little shoot multiplication. Plant development changes depending on nutrient concentration, sugar concentration and hormone balance. Using separate stages allows the grower to control those developmental signals.
A useful way to think about the system is:
Establishment → Survive and become clean
Multiplication → Produce more shoots
Rooting → Build an independent plant
Acclimation → Adapt to normal growing conditions
That sequence is one of the fundamental ideas behind micropropagation.