Management Methods and Technical Key Points for the Color-Changing Stage of Shiitake Mushrooms

When the shiitake mushroom mycelium grows and develops into the physiological maturity stage, the white mycelium on the surface gradually turns into a brown layer of mycelial film under certain conditions, which is called mycelial color change. The depth of the color change and the thickness of the mycelial film directly affect the occurrence and development of shiitake mushroom primordia, and have a great relationship with the yield and quality of shiitake mushrooms. It is the most important link in the management of shiitake mushroom fruiting.

There are many methods for color change, and the commonly used one is the bag-removal color-change method. It is necessary to accurately grasp the timing of bag removal, that is, remove the bag when the mycelium reaches physiological maturity. If the bag is removed too early, it is not easy to change color; if too late, the mycelium ages, often produces yellow water, and is prone to contamination by miscellaneous bacteria, or the mycelial film thickens, making the differentiation of shiitake mushroom primordia difficult. The temperature at the time of bag removal should be 15-25°C, preferably 20°C. Before removing the bags, first make beds 30-40 cm deep and 100 cm wide on the floor of the fruiting greenhouse. Spread a layer of furnace ash or sand on the bottom of the beds. Transport the bags to be removed and color-changed into the greenhouse, cut open the bags with a blade, remove the plastic bags, and stand the cylindrical mycelial blocks upright in the beds at a spacing of 5-8 cm. If the long mycelial columns stand unsteadily, bamboo poles can be used to build a horizontal frame over the bed, and the mycelial columns can be leaned against the bamboo poles at an angle of 70-80 degrees. After bag removal, the mycelial columns should be protected from sunlight and wind. At this time, the relative air humidity in the greenhouse should preferably be controlled at 75%-80%. Mycelial columns with yellow water can be rinsed clean with clear water. Bag removal and standing of the mycelial columns should be done quickly. As soon as one bed is filled, immediately arch bamboo strips over the top of the bed, cover with plastic film, and press the surroundings tightly to retain moisture and heat. After all the mycelial columns are arranged, the greenhouse temperature should be controlled at 17-20°C, and should not exceed 25°C. If the temperature is high, spray cold water into the greenhouse space to cool it down. Add more shading during the day, remove the shading at night, and strengthen ventilation to cool down. The light should be dimmer. For the first 3-5 days, try not to uncover the cover film on the beds. At this time, the relative humidity in the beds should be 85%-90%, and condensed water droplets should be on the plastic film, allowing the mycelium to continue growing in a warm, humid, and stable environment. Note that during this period, if the temperature is high and the humidity is too great, the cover film on the beds should still be uncovered for ventilation for 20 minutes each day in the early morning and evening when the temperature is low. When uncovering the cover film on the beds for ventilation, the greenhouse should not be ventilated at the same time; the ventilation times of the two should be staggered. At 5-7 days after the mycelial columns are stood upright, when the surface of the mycelial columns is covered with thick white fluffy aerial mycelium, increase the number of times of uncovering the film for ventilation, 2-3 times a day, 20-30 minutes each time, to increase oxygen and light (scattered light), widen the dry-wet difference on the surface of the mycelial columns, limit mycelial growth, and promote color change. When color change begins at 7-8 days, ventilation can be increased, with each ventilation lasting 1 hour. Along with ventilation, lightly spray water on the surface of the mycelial columns 1-2 times a day. After spraying water, let them air for 1 hour before covering the film again. Spray water continuously for 2 days, and color change is completed by 10-12 days. In production practice, due to different sowing seasons and different climatic conditions, especially temperature conditions, at the color-change site, the speed of color change is not the same. Specific operations should be flexibly controlled according to the growth of mycelium on the surface of the mycelial columns.

Common abnormal phenomena during the color-change process and their treatment methods.

① The color change is too light or does not occur at all: If the mycelial columns are exposed to sunlight or dry wind during bag removal, causing the surface of the mycelial columns to be too dry, spray water on the mycelial columns to restore the moisture on their surface, cover the film well, reduce the number of ventilations and shorten ventilation time. Ventilate 1-2 times a day, 10-20 minutes each time. If the relative air humidity in the space is too low or the temperature is below 12°C, or above 28°C, timely measures should be taken to increase humidity and control temperature, trying to keep the humidity in the beds at 85%-90% and the temperature at 15-25°C.

② The mycelium on the surface of the mycelial columns keeps growing vigorously and does not lie down or change color even when it reaches 2 mm: The cause of this phenomenon is lack of oxygen. Although the temperature is suitable, the humidity is too high, or the nitrogen content of the culture material is too high, etc. This requires extending ventilation time, letting light shine on the mycelial columns, increasing the dry-wet difference on their surface, and forcing the mycelium to lie down. If there is still no effect, 3% lime water can also be sprayed on the mycelial columns, and after airing until the surface of the mycelial columns is no longer sticky and slippery, cover the film again and resume normal management.

③ The mycelium dehydrates, and the surface of the mycelial columns feels prickly when touched by hand: Spraying water can be used to increase the relative air humidity and the moisture on the surface of the mycelial columns, so that the relative air humidity inside the cover film remains at 85%-90%.

④ About two days after bag removal, the tumor-like mycelium on the surface of the mycelial columns produces bubbles and swells, partially peeling off in patches, or partially detaching from the mycelial columns to form a hanging shape: The main causes of this phenomenon are external force damage during bag removal or the influence of high temperature (28°C), or it may also be caused by removing the bag too early, insufficient mycelial age, and mycelium not yet mature, unable to adapt to the changed environment. The solution is to strictly control the temperature at 15-25°C and the relative air humidity at 85%-90%, promote new mycelium to grow again on the surface of the mycelial columns, and then promote color change.

⑤ When contamination by miscellaneous bacteria is found on the mycelial columns, spray them with Type II Kemeiling at a 1:500 dilution, once a day, for 3 consecutive days. After each spraying, let them air slightly before covering the film again.

In addition to bag-removal color change, some production practices use the needle-prick micro-hole aeration color-change method, and after color change, remove the bags for fruiting. Others do not remove the bags. When shiitake mushroom fruiting body primordia appear around the inoculation holes of the bags, cut the plastic bag around the primordia with a knife to expose the primordia and carry out fruiting management. After the first flush of mushrooms is finished, the color change of the entire bag is completed, and then the bag is removed and soaked in water to produce the second flush of mushrooms. These color-change methods are simple and retain moisture well. Using this method for color change in high-temperature seasons can reduce contamination by miscellaneous bacteria.