Fungal spores are microscopic reproductive cells, similar to the seeds of plants, which allow the organism to disperse and colonize new areas. In cultivation, these spores represent the starting point for growing a new generation of mushrooms. The process requires a clean, controlled environment to ensure the desired fungus can outgrow competing organisms present in the air and on surfaces. Cultivating spores is a multi-stage process that demands patience and attention to detail.
Essential Preparation and Sterilization
Success in growing spores rests almost entirely on maintaining an impeccably sterile environment, as contamination accounts for the majority of beginner failures. Cultivators must first assemble a controlled workspace, such as a Still Air Box (SAB), which is a sealed plastic tote designed to minimize airborne particles during transfers. All surfaces within this box, along with gloves and tools, must be disinfected using 70% isopropyl alcohol.
The growth medium, often a nutrient-rich grain like rye or millet, requires complete sterilization to eliminate all competing microbes, including heat-resistant bacterial endospores. This is typically achieved using a pressure cooker or autoclave that reaches 121°C (250°F). This temperature is maintained by holding the pressure at 15 pounds per square inch (psi) for 90 minutes to two hours, depending on the substrate volume. This process ensures the grain is a sterile food source, giving the fungal spores an uncontested environment for germination.
Techniques for Spore Inoculation
The actual transfer of spores into the sterile substrate must occur within the Still Air Box to prevent the introduction of airborne contaminants. One common method uses a spore syringe, which contains spores suspended in sterile water. The needle tip is flame-sterilized until it glows red, allowed to cool, and then inserted through a self-healing injection port on the grain container.
A small volume, typically 1 to 2 milliliters of the spore solution, is injected into the grain, and the container is gently rotated to distribute the spores. Alternatively, spores can be germinated first on a nutrient-rich agar plate for more controlled growth. This involves using a flame-sterilized scalpel to scrape a few microscopic specks of spores from a spore print onto the center of the agar medium. The lid is then quickly replaced to minimize exposure to outside air.
Incubation and Monitoring Mycelial Development
Following inoculation, the substrate enters the incubation phase, encouraging spores to germinate and develop into mycelium, a dense network of thread-like cells. This phase requires a stable, dark environment with temperatures maintained between 70°F and 80°F (21°C–27°C) for most species. Consistent warmth is necessary for fungal metabolism, but higher temperatures can promote the growth of unwanted bacteria.
The first signs of growth, appearing seven to fourteen days after inoculation, are bright white, cottony, or rope-like structures spreading across the grain. This healthy mycelium often has a clean, slightly earthy aroma. Contamination is signaled by distinct colors such as green (often Trichoderma mold), blue-green, or black, or by a sour, foul odor indicating bacteria. Any container showing foreign growth must be immediately isolated to prevent the spread of spores to other cultures.
Transitioning to Fruiting Conditions
Once the mycelium has completely colonized the substrate, it must be triggered to shift from its vegetative phase to its reproductive phase, producing mushroom fruit bodies. This transition is signaled by introducing environmental changes that mimic natural season cues. The visual indicator that the culture is ready is the appearance of hyphal knots, which are tiny, dense, white clusters of mycelium on the substrate surface.
The environmental triggers for fruiting include a slight temperature drop, typically 68°F to 75°F (20°C–24°C), and a significant increase in relative humidity (90% to 95%). Crucially, the mycelium requires a substantial boost of fresh air exchange (FAE) to reduce built-up carbon dioxide. Cultivators often achieve this controlled microclimate using a Shotgun Fruiting Chamber (SGFC), a plastic container lined with moist perlite and dotted with holes for passive air circulation and high humidity.