Melzer's reagent or Melzer’s solution is a chemical reagent that is used by mycologists to assist with the identification of fungi. The Melzer’s reagent consists of chloral hydrate potassium iodide, and iodine. While Melzer’s reagent is an effective tool in the mycologists tool box, it is difficult to obtain due to chloral hydrate being a regulated narcotic in many countries including the US. To ameliorate problems with obtaining chloral hydrate, Visikol has developed Visikol® for Plant Biology™ which can be used in a modified protocol to replace Melzer’s Reagent. Visikol® for Plant Biology™ was originally developed as a tissue clearing reagent for plant tissues as a replacement to chloral hydrate and can be adapted as a replacement for chloral hydrate in Melzer’s reagent.
Typically, Melzer’s reagent works by exposing fungal tissue or cells to the reagent on a microscope slide and looking for the color of the reaction:
1) Blue to Black – Amyloid or Melzer’s positive
2) Brown to Reddish Brown - Pseudoamyloid or dextrinoid reaction
3) No change or yellow-brown – Amyloid or Melzer’s negative
Amyloid positive fungi can be furthered identified based upon their color change with the addition of a potassium hydroxide pretreatment step.
1) Blue without pretreatment - Euamyloid reaction
2) Red in Lugols solution/ Blue in Lugols or Melzer’s with pretreatment - Hemiamyloid reaction
Replacement for Melzer’s Reagent Protocol
1. Crush sample in ethanol using mortar and pestle so that it is fine enough for a microscope slide. If the sample is already a scraping or fine enough for microscope visualization only wash in ethanol.
2. Let sample air dry or gently heat.
3. Place drop of iodine solution (lugols) on sample and then let it air dry or gently heat.
4. Place Visikol® for Plant Biology™ on sample until clear and let dry.
5. Mount sample in 100% glycerol (non-permanent) or permanent mounting solution (e.g. Visikol® Mount™)
6. Visualize sample on microscope.
**If conducting pretreatment with KOH, solution pH must be neutralized before proceeding with protocol**