Should Tissue-Cultured Plantlets Be Root-Pruned Before Transplanting? What Research Says
- นภสร ตาปะสี
- 51 minutes ago
- 5 min read
Root pruning before transplanting tissue-cultured plantlets should not be treated as a standard procedure for every species. Roots formed in vitro are not automatically useless once a plant leaves the culture vessel.
Research shows that some in vitro roots can continue absorbing water and help maintain plant water balance during the critical early stage of acclimatization. At the same time, certain species respond well to partial root pruning and are capable of rapidly producing new roots under ex vitro conditions.
The correct approach therefore depends on plant species, root quality, rooting capacity, and the acclimatization system, rather than on a single rule applied to all tissue-cultured plants.
Evidence from Grapevine: Partial Root Pruning May Help, but Complete Removal Is Not Necessary
One of the studies that addressed this question directly was conducted by Thomas and Ravindra using grapevine (Vitis vinifera).
The researchers compared plantlets in which:
In vitro roots were retained
Roots were partially pruned
In vitro roots were completely removed
All treatments achieved establishment rates above 90%. However, plantlets that had all roots removed showed weaker early growth than those that retained at least part of their original root system.
Interestingly, the root-pruned group produced more new roots around the stem base and showed improved plant uniformity.
This supports an important distinction: partial root trimming may be beneficial in some species, but complete root removal is not automatically necessary or advantageous.
In Vitro Roots May Differ from Roots Formed Outside the Vessel
One reason some laboratories prune roots is that roots formed under in vitro conditions may differ anatomically and physiologically from roots formed in soil or nursery substrates.
Research in woody plants has shown that some in vitro roots may have relatively large cortical cells and incompletely developed vascular tissues. After transfer from the vessel, some of these roots may stop growing or die, while the plant gradually forms a new root system better adapted to ex vitro conditions.
This means that a plantlet with many roots inside the vessel does not necessarily have the most effective root system after transplantation.
More useful indicators include:
Root branching
Presence of lateral roots
Fine root development
Root-tip health
Root color and firmness
Capacity to initiate new roots after transfer
Root quality matters more than root number alone.
In Vitro Roots Can Still Be Functional
The opposite assumption—that in vitro roots are essentially disposable—is also incorrect.
Research on micropropagated apple plants has shown that plantlets with established in vitro roots maintained better water status than unrooted shoots, particularly during the transition from the high-humidity culture vessel to the drier greenhouse environment.
This is biologically important because acclimatization already exposes plantlets to increased water loss through their leaves. If healthy roots are removed at the same time, the plant experiences two major stresses simultaneously:
Reduced water uptake because the root system has been removed
Increased water loss as the plant adapts to lower humidity
For this reason, when roots are white or cream-colored, firm, healthy, and free from rot, retaining them is often safer than removing them without species-specific evidence.
Ex Vitro Rooting Is a Different Strategy
Another useful approach is ex vitro rooting, where unrooted shoots are removed from culture and allowed to form roots while acclimatizing outside the vessel.
This is fundamentally different from producing roots in vitro and then cutting them off.
For example, research involving Philodendron pedatum found that shoots rooted successfully in peat-based substrate outside the culture vessel and developed functional root systems during acclimatization.
This suggests that some Philodendron species may not require a separate in vitro rooting stage at all, provided that greenhouse humidity, temperature, substrate moisture, and environmental conditions are carefully controlled.
Ex vitro rooting can potentially reduce production time and laboratory costs, but it must be tested separately for each species or cultivar.
Anthurium, Banana, and Pineapple Often Benefit from Retaining Healthy Roots
For several commercially important crops, available evidence and standard acclimatization practice generally support preserving healthy roots before transplantation.
In Anthurium andraeanum, successful acclimatization protocols commonly involve carefully washing culture medium from the roots while avoiding unnecessary root injury.
Banana plantlets also benefit from well-developed root systems containing primary roots, lateral roots, and root hairs during hardening.
Similarly, pineapple plantlets with several strong roots can establish successfully in growing media without routine root removal.
For example, if a banana plantlet has clean, white, branched roots that are not excessively tangled, carefully washing away the agar and preserving the roots is more biologically reasonable than removing the entire root system.
Root Management Should Be Based on Root Quality
A practical commercial approach is to classify roots according to their condition before deciding whether pruning is necessary.
Healthy Roots
Roots that are white to cream-colored, firm, actively growing, and well branched should generally be retained.
Excessively Long or Tangled Roots
Roots that are healthy but too long or tangled to fit properly into a plug tray or substrate may be trimmed moderately for easier planting.
The objective is to improve handling—not to reduce every root to a predetermined length.
Mechanically Damaged Roots
If root tips are bruised, torn, or crushed during agar removal, only the damaged portions may be removed.
Diseased or Necrotic Roots
Black, soft, rotten, translucent, or severely damaged roots should be removed because they may deteriorate further after transplantation.
For example, a Philodendron plantlet with healthy roots 8–10 cm long does not need to be cut back to 1–2 cm simply because the roots are long. The roots may instead be arranged carefully in the substrate or trimmed only enough to allow proper planting.
Root Trimming and Total Root Removal Are Not the Same
This distinction is critical.
Root trimming means removing only part of the root system, usually damaged, excessively long, or inconvenient sections.
Total root removal means eliminating the entire root system and forcing the plant to regenerate new roots after transplanting.
Partial pruning may sometimes stimulate new root production and improve root architecture. Complete removal imposes a much greater physiological stress, particularly during acclimatization.
Fast-rooting plants such as some Philodendron cultivars may recover relatively quickly. Slow-rooting species may lose more from root removal than they gain.
Where species-specific evidence is unavailable, moderate root trimming is a more defensible approach than complete root removal.
A Better Commercial SOP: Assess Roots Before Cutting
Commercial laboratories should avoid an SOP that simply states:
“Wash off the agar and cut the roots from every plantlet.”
A better system is to evaluate root quality before transplantation and only prune when justified.
A trial can compare four treatments:
No root pruning
Light root trimming
Severe root trimming
Complete root removal
The laboratory should then monitor:
Survival percentage
Wilting after transplant
Time to new root initiation
Number of new roots
Root length and branching
New leaf production
Plant height
Biomass development
Time required to reach saleable size
This matters because different treatments may achieve similar survival rates while producing very different root systems and recovery speeds.
A plant that survives but remains stagnant for several weeks is not commercially equivalent to a plant that rapidly develops new roots and resumes growth.
Root Quality Is More Important Than a Universal Cutting Rule
The available evidence does not support treating complete root removal as a universal requirement before transplanting tissue-cultured plants.
A more practical guideline is:
If the roots are healthy, retain them.
If the roots are excessively long or tangled, trim only as needed.
If the roots are damaged or rotten, remove the affected sections.
If ex vitro rooting is being considered, test it as a separate production system.
Do not make total root removal a standard procedure without species-specific evidence.
Ultimately, the decision should be based on how the plant performs after transplantation, not on how tidy the roots look before planting.
For commercial production, the best treatment is the one that delivers the highest number of healthy, rapidly establishing, marketable plants—not simply the one that produces the highest immediate survival percentage.
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