Contamination in mushroom cultivation

Article title : Common contamination in mushroom cultivation?

Article link : https://northspore.com/blogs/the-black-trumpet/common-contamination-in-mushroom-cultivation

Publication : Will Broussard on 02/01/2024 for NorthSpore

Whether you're a mushroom hobbyist or grower, the number one cause of harvest failure is contamination. Contamination refers to any element present in your substrate or in the mycelium that negatively impacts your culture, and can include bacteria, mold and animal parasites.

In this article, we'll review common sources of contamination in mushroom growing, highlight five common contaminants, and offer tips for reducing contamination in your future growing operations. This way you will know if your mushrooms are contaminated or not, how it could have happened and how to prevent it from happening again in the future!

What are the basic signs of contamination? Before we get into it, here is a list of the basic signs of contamination in mushroom growing:

• Discoloration: Changes in color, such as yellow or brown spots on the surface of mushrooms or growing medium.

• Abnormal odors: A strong, foul odor emanating from the culture vessels or growth medium.

• Abnormal growth: Mushrooms that grow abnormally, such as those that are misshapen or stunted.

• Presence of mold: Appearance of mold, such as white or blue-green growths on the surface of mushrooms or growth medium.

• Presence of insects: Presence of insects, such as flies or mites, on the substrate or fruit bodies.

If you notice any of these signs, it is important to act immediately to prevent further contamination. This may involve ditching your containers, disinfecting the growing area, or adjusting growing conditions to improve the overall health of your crop.

Sterile technique, or “tek,” refers to the process of maintaining a clean environment throughout the cultivation process. Use sterilized equipment, grow only on sterilized substrates, and maintain a clean, controlled environment at all times.

• Airborne contamination: Fungi reproduce by spores, which are microscopic cells released from the fungus and dispersed most often in the air. They can remain viable for long periods of time, in some cases indefinitely. The best way to reduce unwanted spores and other airborne contamination in your workspace is to use a laminar flow hood, which is a work bench that includes a filter pad, fan, and HEPA (air particulate matter) filter. high efficiency) integrated.
• Substrate Contamination: Mushroom substrates are the perfect breeding ground for unwanted microbes. If not properly treated by pasteurization or sterilization, contamination will result in lost harvests. Different species prefer different treatments, the first option includes pasteurization and the second sterilization using a pressure sterilizer.
• Human-caused contamination: The human body is the greatest source of contamination in mushroom cultivation. Human hands and clothing contain a lot of bacteria and spores that can ruin a crop. Before starting work, use hand sanitizer, for example.

While mycelium is usually white and stringy or cottony, contamination usually takes the form of green, blue, gray or black spots or discolorations in your substrate. Keep in mind that blue spots on some types of mycelium may simply be natural bruising and not contamination, especially if the substrate presses the mycelium against glass or plastic. A simple tip to determine whether or not your discoloration is contaminated is to gently run a cotton swab over it, as contamination will transfer to the cotton swab while bruises will not.

Here are five of the most common contaminants encountered in mushroom cultivation:

1. Trichoderma: Trichoderma harzianum is commonly seen in mushroom cultivation. It produces green spots that can quickly cover substrates, distinguished by its fluffy appearance. This contamination can occur at any stage of cultivation and can cause significant damage by feeding on the cultivated species. To counter Trichoderma, it is essential to immediately isolate and eliminate contaminated substrates, disinfecting affected tools. Prevention involves adequate ventilation, a clean environment, and constant monitoring for signs of contamination. Unfortunately, once detected, Trichoderma control is often difficult, sometimes requiring starting cultivation from scratch.

2. Orange Bread Mold: Orange bread mold, red bread mold or pink mold are alternative names for Neurospora crassa, this neon orange mold can wreak havoc on your operation in just 8 to 12 hours. It first appears as an orange-white flake but quickly develops into a bright orange powdery spot. Once found, contain the source by sealing it in a plastic bag and discard it immediately, being careful not to disturb the mold as it will release a fine cloud of orange spores into the air which can spread quickly. After disposal, disinfect the affected area and inspect your workspace for the source, which could include discarded coffee grounds, compost, or damp, untreated wood.

3. Bacillus spp. (Bacterial Contamination): The most common form of bacterial contamination in mushroom cultivation is known as "wet spot" or "sour rot." It is characterized by a dull gray ooze with a musty odor that appears excessively wet or slimy and often forms in uncolonized spots along the bottom of grain jars. Their reproductive structures are called endospores, which are heat resistant, meaning they will survive the sterilization process. To prevent them, grains can be soaked for 12 to 24 hours at room temperature before sterilization, allowing endospores in the grain to germinate and be removed during sterilization. If contamination is encountered, it is possible to separate it from the rest of the mycelial grains (as long as the stain is small and confined to one area) by physically removing the stain using a spoon previously disinfected with alcohol or sterilized by flame. This can also occur in a monotub with an isolated spot of contamination where the fungus exudate has turned the affected area yellow, indicating an attempt by the fungus to fight off the rival bacteria.

4. Spider Mold: Spider mold (Hypomyces rosellus) is another species of harmful fungi that can be encountered in mushroom growing, especially in environments with stagnant air, very little oxygen and high humidity such as grain jars and monotubs. It can be difficult to detect due to its gray, white, fluffy appearance that resembles mycelium, but its growth pattern is more three-dimensional, appearing to float above the substrate in white clumps. Additionally, this mold often forms in the last days of incubation, when the substrates are fully colonized just before fruiting. Spider mold spreads quickly: a small spot the size of a dime can grow to cover an entire jar or monotub in 24 to 48 hours. Growers can prevent spider mold by lowering the humidity in their grow rooms and monotubs, which can be accomplished by paying attention to substrate hydration and improving fresh air exchange. After soaking a paper towel in hydrogen peroxide and placing it on the affected area to control future spider mold contamination.

5. Black Bread Mold: Also known as pinhead mold, black bread mold (Rhizopus stolonifer) is a common fungal contaminant in soil and air and is one of the first molds to appear on stale bread. This fast-growing mushroom has dense mycelium that is first white and turns gray and then takes on a black appearance. Similar to spider mold, black bread mold is fuzzy but develops small black dots at the end of its mycelium where its spores are produced. Spraying with hydrogen peroxide can help contain the early spread of most molds, including this one, but once the mold advances to the stage where it is easily identifiable, it may be too late for cultivation. At this point, the best way to deal with it is to abandon it and start again.

Mushroom growers all encounter contamination sooner or later, so it's good to learn how to identify common contaminants and how to develop a rigorous sterilization technique.