Contamination is one of the main causes of loss in plant tissue culture. Bacteria and fungi can consume nutrients, alter the chemistry of the medium, damage explants and spread rapidly through cultures. Effective control requires identifying where contamination enters the workflow rather than relying on sterilisation intensity alone.
Surface contamination
Plant material entering culture carries microorganisms on external surfaces. Surface disinfection aims to reduce this microbial load while preserving living plant tissue. Increasing disinfectant concentration or exposure time can improve microbial control but can also injure the explant, so establishment protocols require a balance between disinfection and phytotoxicity.
Endophytic and internal contamination
Some microorganisms occur inside apparently healthy plant tissues. Surface treatment cannot reliably remove organisms already protected within the explant. Internal contamination may appear only after days or weeks in culture, particularly as microorganisms multiply in nutrient-rich medium.
Procedural contamination
Contamination can also be introduced during media preparation, vessel handling, transfers or subculture. Hands, tools, vessel rims, airflow disturbances and contaminated work surfaces can all move microorganisms into sterile material.
Aseptic technique
Aseptic technique is a system of behaviours designed to prevent microorganisms reaching sterile media and plant tissue. Work should be organised so sterile items spend minimal time exposed, tools are appropriately sterilised between manipulations, vessel openings are controlled and hands do not pass unnecessarily over sterile work.
Laminar-flow workspaces
A correctly functioning clean-air workspace reduces airborne particle deposition across the working area, but it does not make poor technique sterile. Objects placed into the workspace can carry contamination, and obstructing clean airflow can create turbulence around critical areas.
Media sterilisation
Heat-stable media components and vessels are commonly sterilised using moist heat under pressure. Sterilisation performance depends on temperature, exposure time, load configuration and heat penetration. A cycle should be designed around the material being sterilised rather than pressure alone.
Recognising contamination
Fungal contamination may become visible as filamentous growth, while bacterial contamination can appear as cloudy films, colonies or material spreading around an explant. Appearance alone is not always sufficient for identification, and some contamination remains subtle during early stages.
Why contamination sometimes appears late
A low initial microbial population can remain visually undetectable until it has multiplied sufficiently. Slow-growing internal contaminants can also become apparent only after repeated subculture. A culture that looked clean immediately after establishment was therefore not necessarily sterile.
Reducing losses systematically
Track contamination by batch, source plant, operator, medium and stage. If contamination clusters around one explant source, internal or surface microbial load becomes more plausible. If unrelated cultures fail immediately after the same transfer session, workflow or equipment should be investigated.
Continue with our guide to plant tissue culture and micropropagation and tissue-culture acclimation.