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-🧪 Melzer’s reagent helps identify fungal traits like amyloidity and dextrinoidity by staining spores with iodine.
-⚠️ Chloral hydrate, a main ingredient, is restricted in many countries because it is a sedative.
-🔍 Genera like Amanita and Russula react in special ways to Melzer’s reagent, which helps identify them accurately.
-🥼 Modified Melzer’s and Lugol’s iodine are safer options for both professionals and hobbyists.
-🧬 DNA barcoding is standard now, but Melzer’s is still useful for microscopy and teaching.
Today, mushroom enthusiasts and professionals still use Melzer’s reagent—an old iodine-based stain—for identifying fungi, even though DNA sequencing and molecular markers are now common. The tools for fungal identification have expanded, but Melzer’s is still especially good at revealing microscopic details such as amyloidity. Whether you're studying wild specimens or checking cultures grown in Mushroom Grow Bags or a Monotub, these subtle reactions can help confirm a mushroom’s genus and species with accuracy.
Melzer’s Reagent: A Common Iodine Tool for Fungi
Simply put, Melzer’s reagent is a special chemical stain. It helps find certain fungal parts by making them change color when it touches starch-like things or cell walls. It is especially useful under a microscope. Here, these color changes show important small details. Think of it like a litmus test—but for mushroom spores.
Melzer’s is mainly used to check how spores, asci, or hyphae react. This helps tell the difference between:
- Amyloid reactions: Color change to bluish-black.
- Dextrinoid reactions: Rusty red to mahogany brown coloration.
- Inamyloid reactions: No color change when iodine touches them.
These reactions are important features in naming fungi, especially for white-spored mushrooms or ascomycetes.
History: Václav Melzer and Where the Reagent Came From
Czech mycologist Václav Melzer made this reagent in the early 1900s. It quickly became a standard tool for studying fungi. At that time, DNA sequencing was not even thought of. Microscopy and chemical staining were the best ways for taxonomists to identify fungi.
Melzer saw that some fungal tissues reacted in special ways to iodine, changing colors that helped identify them. This gave a new way to group fungi, not just by what you could see with your eyes—like cap color and spore print. It also grouped them by tiny, unseen details. These details helped tell apart species that were very similar.
Because Melzer’s reagent could show spore features, many people started using it, especially for white-spored groups like Lepiota, Amanita, and Russula. Today, it shows how old microscopy methods are still important in science today.
What’s in Melzer’s Reagent?
Melzer’s reagent has three main ingredients:
- Iodine (I₂): This is the part that makes colors change in fungal tissues.
- Potassium iodide (KI): It dissolves iodine and helps keep the mix steady.
- Chloral hydrate (C₂H₃Cl₃O₂): It makes tissue clear by making it less cloudy under a microscope, which helps you see the slide better.
These ingredients work together to show how fungal cell walls are different.
But chloral hydrate is the most talked-about part. It is a sedative drug that many countries control because it affects the mind. In the U.S., it is on a list of controlled drugs. This makes it harder for schools and people to get and store.
This has led to looking for other ways to make it. These new ways would work as well as Melzer’s but use safer ingredients that are easier to get.
Spore Reactions: Amyloid, Dextrinoid, and Inamyloid
Spore reactions to Melzer’s reagent are important clues in naming fungi. Here’s how each reaction looks and what it means:
Amyloid Reaction
- Color Shift: Spores or structures stain bluish to black.
- Shows: Starch-like compounds or certain sugar structures are present.
- Found in: Groups like Amanita, Russula, and many Ascomycota (especially their asci).
Dextrinoid Reaction
- Color Shift: Spores or tissues turn reddish-brown or mahogany.
- Shows: Complex sugar reactions happen, but we understand this less than amyloid reactions.
- Found in: The group Lepiota, some Entoloma, and Lentinellus species.
Inamyloid Reaction
- Color Shift: No visible change when iodine touches them.
- Shows: No starch-like reactions are happening.
- Found in: Many white-spored fungi that are not amyloid, and many basidiomycetes.
Knowing these reactions is very important for finding the right genus or species. In some groups, like the Russulaceae, amyloid spore patterns are a main way to identify them.
Which Groups React Best to Melzer’s?
1. Amanita
White-spored Amanita species often show strong amyloid reactions, especially in the spore walls. This helps tell poisonous kinds from edible ones. For example, Amanita phalloides (the death cap) has amyloid spores.
2. Russula and Lactarius
Both groups show amyloid reactions in their spore wall patterns. These often look like nets or warts when seen up close.
3. Lepiota
Species in this group may show dextrinoid reactions. This can help separate them from toxic or edible species that look similar.
4. Ascomycetes
Many ascomycetes show amyloid reactions in their asci, not always in spores. This is very useful when identifying them under a microscope.
5. Others
Groups like Entoloma and Lentinellus can show different reactions. Also, many fungi that decay wood have weak or confusing Melzer reactions, so you need to use other methods too.
Safety and Use: Is Melzer’s Safe?
Ingredient Concerns:
- Chloral Hydrate Use: It is a controlled substance in places like Canada, the EU, and various U.S. states. So, how you store and use it is watched.
- Toxicity Risk: If it touches skin or you breathe its fumes, it can cause irritation or make you sleepy. You need to wear gloves, have good air flow, and follow storage rules.
Recommendations:
- For Labs & Educators: Get a license to use chemicals if you need one, and store it as rules say.
- For Hobbyists: Look for changed recipes or use safety gear. Keep it away from children and animals.
Disposal:
Never pour Melzer’s down the drain. Rules for throwing away hazardous waste in your area should tell you how to get rid of unused reagent.
Other Choices Instead of Melzer’s Reagent
When you can't get classic Melzer’s or don't want to use it, these are common substitutes:
1. Lugol’s Iodine
- Pros: Easier to find, not controlled.
- Cons: It does not always give clear amyloid/dextrinoid reactions.
2. Modified Melzer’s Reagent
- Uses sodium lauryl sulfate or lactic acid instead of chloral hydrate.
- It works just as well for many tests and is legal in places with stricter rules.
3. Chlor-Zinc-Iodine (Schulze’s Solution)
- Used in plant tissue study. It is sometimes mentioned for fungal ID, but not used as often.
4. Cotton Blue or Lactophenol Solutions
- These are stains used to see hyphae and spore patterns, but not specifically for amyloid tests.
5. Euparal (Common Mistake)
- This is not a reagent but a slide glue. Sometimes people wrongly think it is a test liquid.
Changed Melzer’s recipes are your best choice for keeping things clear to see and for safety.
DNA Tests vs. Old Reagents
Molecular mycology has grown. This means DNA sequencing (often looking at ITS regions) is now more precise than reagents. But:
- 🎯 DNA methods are very accurate.
- 💸 Challenge: You need special equipment, training, and money.
- 🧪 Melzer’s Reagent: Lets you identify fungi based on their shape without needing lab work.
Because of this, many field guides and amateur mycologists still suggest Melzer’s for quick checks and confirming what something is, even with or without genetic backup.
Using Melzer’s for Fungi at Home
If you grow things in your backyard, are part of amateur identification groups, or use kits from companies like Zombie Mushrooms, Melzer’s reagent can make your learning and experience better.
How To Use: Simple Steps
- Make a spore print by placing a mushroom cap on foil or glass, gills face down.
- Let sit overnight to collect spores.
- Use a toothpick to transfer a portion of the print onto a microscope slide.
- Add 1 drop of Melzer’s or Lugol’s iodine.
- Cover with a slip; observe under 400x magnification or higher.
- Watch for color change and document it with photos.
This process brings fungal identification into your home, connecting a hobby with science.
Where to Buy Melzer’s Reagent
How you can buy it may be different, depending on local laws.
In the USA
- You can buy it from science suppliers like Carolina Biological, online microscope stores, or special mushroom shops.
- Some school kits have it or changed recipes.
Europe & Canada
- There are limits on chloral hydrate.
- Look at local online groups or for legal changed Melzer’s options to buy.
Always check for:
- Correct labels for ingredients.
- Safe packaging.
- If an MSDS (Materials Safety Data Sheet) is available.
Store it in a cool, dry, dark place, away from too much sunlight or heat.
What We Think Today
Melzer’s reagent is not old-fashioned, and anyone can use it. It is still useful for studying fungi under a microscope, for learning, and for people with hobbies.
It will not replace DNA sequencing—but it does not need to.
If you use it wisely, and know its risks and limits, Melzer’s can make you feel more connected to fungi. You can see their detailed spores and find their hidden chemical signs.
Whether you are trying to identify a Russula, confirm a spore reaction in an Amanita, or learn about your grow kit's biology, this iodine classic is still important. It works best when you use it with other new tools.
Citations
Largent, D. L., Johnson, D., & Watling, R. (1977). How to Identify Mushrooms to Genus I: Macroscopic Features. Mad River Press.
Krieglsteiner, L. (2003). Sporenreaktionen in Melzer’s Reagenz. Zeitschrift für Mykologie, 69(1), 25-30.
Baroni, T. J. (1981). The use of Melzer’s reagent in identifying white-spored agarics. Mycologia, 73(5), 933-944.
O’Donnell, K., & Cigelnik, E. (1997). Two-locus phylogenetic analysis of the Fusarium species complex. Applied Environmental Microbiology, 63(5), 1733–1743.
