Penicillium, commonly known as green mold, is a genus of fungi that includes several species frequently encountered in the production of edible mushrooms. Among them are *Penicillium frequentans*, *P. lilacinum*, *P. viridicatum*, and *P. chrysogenum*, as well as *P. verruculosum*. These fungi can invade and damage oyster mushrooms, shiitake, and other edible fungi during the seed production and cultivation phases.
**1. Symptoms of Damage**
In the early stages of infection, the mycelium of Penicillium closely resembles that of the edible fungus, making it difficult to distinguish between the two. However, once conidia are formed, Penicillium develops a characteristic pale blue or green powder-like appearance. When it infects the mushroom bed or culture medium, it inhibits the growth of the edible mushroom’s mycelium, preventing fruit body formation. Even if fruiting bodies do develop, they often turn brown and rot prematurely.
**2. Morphological Features**
The mycelium of Penicillium is usually colorless or light-colored and appears fragmented. The conidiophores are erect and resemble bristles, with symmetrical bifurcations or multiple branches. At the tips, small stems lead to clusters of conidiospores. The conidia themselves are typically spherical or oval, single-celled, and may have smooth or rough surfaces. They range in color from colorless to green or other shades. The colonies often appear green, yellow-green, or blue, and new white growth rings are commonly found on the outer edges.
**3. Occurrence Patterns**
Penicillium is highly adaptable, widely distributed, and produces large quantities of spores that spread through air, soil, fertilizers, and plant debris. It is not only a common fungus in edible mushroom cultivation but also a major pathogen affecting agricultural products. It can cause mold growth during storage, fruit rot, and deterioration of flower bulbs. This fungus thrives in temperatures between 20–30°C, with humidity above 90%, and prefers acidic environments.
**4. Prevention and Control Measures**
Maintaining good hygiene in the growing area is essential. Keep the surroundings clean and dispose of waste regularly. Inoculation rooms and mushroom houses should be cleaned and disinfected properly. Operators must ensure thorough sterilization during the seed production process, and handled bagged strains should be treated carefully to avoid plastic bag rupture. Regular inspections are necessary, and any contaminated strains should be removed immediately. Never use materials infected with Penicillium.
If Penicillium appears on the culture medium, improve ventilation and reduce moisture by keeping the room temperature around 20–22°C. Once the infection is controlled, normal management can resume. Adjusting the pH by adding 1–3% quicklime or spraying 2% lime water during preparation can help suppress its growth. Using fungicides containing 0.1% thiophanate-methyl is also effective. Ensure proper ventilation in the mushroom house and farm to avoid high humidity and temperature. If an outbreak occurs locally, apply 5–10% lime water or sprinkle lime powder on the affected areas. Alternatively, remove the infected part first and then spray a 3–5% copper sulfate solution to eliminate the pathogen.
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