Knudson medium for orchids

Knudson medium is an artificial nutrient medium developed in 1946 by american botanist lewis knudson to germinate orchid seeds and promote growth in sterile conditions. It is one of the most widely used media for cultivating orchids in vitro and is popular for both laboratory and home applications.

What is knudson medium?

Orchids naturally grow in symbiosis with mycorrhizal fungi, which provide essential nutrients. However, reproducing this symbiosis in laboratory conditions is impossible. Knudson medium was developed as a nutrient-rich substitute that supplies all the essential elements needed for seed germination and seedling growth.

Composition of knudson medium

The standard formula includes:

• Sugar: a primary energy source.
• Mineral salts:
  • Potassium nitrate (kno₃) – a nitrogen source.
  • Magnesium sulfate (mgso₄) – provides magnesium and sulfur.
  • Potassium dihydrogen phosphate (kh₂po₄) – supplies phosphorus and potassium.
  • Calcium chloride (cacl₂) – a calcium source.
• Vitamins:
  • Nicotinic acid, thiamine, and pyridoxine to activate metabolic processes.
  • Iron, zinc, manganese, and other elements essential for tissue development.
  • Agar-agar to create a solid medium, preventing seeds or seedlings from sinking.
• Trace elements:
• Gelling agents:

Advantages of using knudson medium

1. Stimulates seed germination:
   • Provides all necessary nutrients for germination, replacing the need for fungal symbiosis.
2. Sterile environment:
   • Creates ideal conditions for growth without risk of bacterial or fungal contamination.
3. Optimal growth conditions:
   • Supports seedling development until they are ready for transplantation into a substrate.
4. Suitable for different orchid species:
   • The formula can be adjusted to meet the specific needs of different orchid types.

Applications of knudson medium

1. Seed germination:
   • Orchid seeds are sterilized (usually with sodium hypochlorite solution).
   • Sterile seeds are placed on the surface of the nutrient medium in petri dishes or test tubes.
2. Seedling growth:
   • The medium supports seedling development until leaves and initial root systems emerge.
3. Transplantation into substrate:
   • Once seedlings reach a suitable size, they are transplanted into a suitable substrate (e.g., bark, sphagnum moss).

How to prepare knudson medium?

Ingredients (example for 1 liter):

• Agar-agar: 10 g
• Sugar: 20 g
• Kh₂po₄: 250 mg
• Mgso₄·7h₂o: 250 mg
• Cacl₂·2h₂o: 250 mg
• Kno₃: 500 mg
• Vitamins (thiamine, nicotinic acid): 1 mg each
• Microelements (e.g., feso₄): 1–2 mg
• Distilled water: 1 l

Steps:

1. Dissolve all components in distilled water.
2. Add agar-agar and heat to fully dissolve it.
3. Pour the solution into sterile containers (petri dishes, test tubes).
4. Sterilize the medium in an autoclave or water bath (15 minutes at 121°c).
5. Cool the medium to allow it to solidify.

Tips for using knudson medium

1. Maintain sterility:
   • Work in sterile conditions to prevent contamination.
2. Monitor temperature:
   • Keep cultures at +20–25°c.
3. Provide adequate light:
   • Ensure soft, diffused lighting for 12–14 hours daily.
4. Transplanting:
   • Transfer seedlings to a substrate once they are large enough for independent growth.

Conclusion

Knudson medium is a critical tool for successfully germinating orchid seeds and cultivating healthy seedlings. It provides the perfect balance of nutrients for growth, eliminating the need for fungal symbiosis. This medium is ideal for propagating rare and decorative orchid species, whether in a laboratory or at home.