What are the common physiological diseases of bag-cultivated shiitake mushrooms?

Physiological diseases, also known as non-infectious diseases, are poor growth phenomena caused by unsuitable growing conditions or the influence of harmful substances in the environment. Although such diseases have no pathogenic agents and are not mutually contagious, once they occur they can cause major losses. In Chunhua, Shaanxi, the most common physiological diseases of bag-cultivated shiitake mushrooms include mycelial thinning, mushroom burning (pile heating), yellow water in the mushroom logs, mushroom log decline, and deformed mushrooms.

1 Mycelial thinning

1.1 Symptoms: mycelial growth is sparse, and the mushroom logs are soft and lack elasticity.

1.2 Causes: ① The substrate had already become moldy before sterilization, the concentration of antibiotics released by contaminating microorganisms was too high, or the activity of contaminating microorganisms changed the pH of the substrate; ② an unsuitable substrate was selected, such as using conifer sawdust that had not been degreased, resulting in excessively high concentrations of oils and terpenes that inhibit shiitake mycelial growth; ③ excessive addition of chemical substances such as magnesium sulfate; ④ lack of certain essential nutrient elements.

1.3 Prevention: select fresh, high-quality substrate and use a reasonable formula, and do not add chemical substances at will; after mixing the substrate, sterilize it promptly and strictly to prevent yeast fermentation from changing the pH of the substrate.

2 Mushroom burning (pile heating)

2.1 Symptoms: the substrate heats up, turns sour, and the mycelium dies. It is prone to occur in the early stage of mycelial growth and during the period of punching holes for aeration.

2.2 Causes: the respiration process of shiitake mycelium consumes oxygen and releases heat. Under conditions of high-density stacking of mushroom logs and poor ventilation, the released heat accumulates, the substrate temperature rises, and the rise in temperature further accelerates metabolism, thus entering a vicious cycle, and punching holes for aeration accelerates this cycle. When the substrate temperature rises above 33°C and oxygen supply falls short of demand, the originally weak microorganisms on the surface or inside the spawn block - yeast - rise to become the dominant microorganisms under anaerobic conditions, the substrate rapidly ferments and acidifies, and the shiitake mycelium dies rapidly.

2.3 Prevention: break up the piles promptly, spread out the mushroom logs, punch holes in batches, and strengthen ventilation.

3 Yellow water in the mushroom logs

3.1 Symptoms: the mycelial nodules cannot normally dry and shrink into a mycelial skin, but instead dissolve into brownish-yellow sauce-like water. Where the yellow liquid flows, rot proceeds from the surface inward, and finally various contaminating microorganisms develop together in the affected areas.

3.2 Causes: under adverse environmental conditions such as high temperature or mechanical damage, the mycelium inside the mycelial nodules autolyzes into a sauce-like liquid. The moisture and nutrients of the yellow liquid favor the reproduction and damage of Penicillium or bacteria, triggering infectious diseases.

3.3 Prevention: ① select varieties with strong stress resistance, such as V26 and V29. ② Mushroom logs should be stacked in a cool, ventilated place. ③ For punching holes for aeration, keep the temperature at 20-25°C, handle gently, punch gently, and place gently to avoid puncturing the mycelial nodules. ④ Use a syringe to draw off the yellow liquid to reduce humidity inside the bag. ⑤ For severely affected ones, remove the bag, remove the decayed material, soak the mushroom log in a 0.05% prochloraz solution for 1 min (minute), drain, then re-bag and punch holes again.

4 Mushroom log decline

4.1 Symptoms: the mycelial skin is hard, the mycelium inside the mushroom log is short and dull, and the substrate crumbles when it meets water. After the first flush of mushrooms, the mushroom log cannot shrink normally, and there is no yield afterward. This symptom is more likely to occur in shiitake mushroom logs managed with bag removal.

4.2 Causes: poor-quality substrate, adverse climate, or poor management causes poor mycelial growth in the later stage, with short residual mycelium that loses the ability to bind the substrate and twist into mycelial cords and form primordia.

4.3 Prevention: ① select varieties with strong stress resistance. ② select high-quality substrate, especially insisting on using gypsum rather than substituting calcium carbonate, and even more so avoid using low-quality bran adulterated with calcium carbonate. ③ strengthen later-stage management: after the mushroom logs are placed in the shed, shading and ventilation for heat dissipation still need to be strengthened in hotter weather to prevent burning of the logs in the later stage.

5 Deformed mushrooms

5.1 Symptoms: the mushroom bodies are abnormal, mainly manifesting as having a stem but no cap, an overly thick stem, or a deformed cap.

5.2 Causes: apart from some genetic reasons, false mushrooms are mainly caused by the primordia forming too deep, a large amount of nutrients being consumed for stem growth, or too high a temperature during bag removal. Excessively high concentrations of harmful gases such as CO2, or failure to cut the bags and induce fruiting in time, causing mechanical compression, are the main causes of deformed caps.

5.3 Prevention: ① select spawn that has undergone strict fruiting trials and maintains excellent varietal characteristics. ② The distribution and orientation of the mushroom shed should fully consider convenience for ventilation, and management should further strengthen ventilation and air exchange. ③ Forcing the first flush of mushrooms should depend on the variety and the moisture content of the mushroom log. For varieties that fruit easily, natural fruiting is advocated, and no pinning induction is needed. For varieties that do not fruit easily or mushroom logs with insufficient moisture content, soak in water to soften the mycelial skin so as to facilitate fruiting, rather than using the method of water injection. For mushroom logs that do not fruit easily but have sufficient moisture, the effect of pinning induction can be achieved in combination with the last punching of holes for aeration. ④ For conventional mushrooms, bag removal should preferably be carried out when the temperature remains below 16°C for 3 d (days) in a row.