Cause Analysis and Diagnosis and Treatment Methods for Mycelial Regression in Oyster Mushrooms

In the autumn and winter seasons of last year, mycelial regression occurred frequently in oyster mushroom production, and there were also sporadic cases this spring and summer. The symptoms of mycelial regression are as follows: the spawn blocks germinate normally, the colonization of the substrate is slower than normal, and growth from the spawn blocks is radial. When the mycelium length reaches 4-5 cm, the mycelium gradually becomes sparser starting from the spawn block, while the mycelium at the growing tips is denser and denser white and continues to develop, with the mycelium behind it fading and thinning accordingly, until finally the surface of the entire mushroom bag appears slightly grayish-white or even devoid of mycelium. At 40 days after inoculation, the mushroom bags appear grayish-white rather than the normal pure white, and no dense mycelium can be seen. After more than 50 days, most do not produce mushrooms, and if pinning occurs at all, it is very sparse. Background of the problem: cottonseed hull substrate, with conventional auxiliary materials such as lime powder, plus a conventional amount of prochloraz, and no other chemicals used; inoculation rate 10%-15%, micro-hole or medium-hole mycelial running, spawn blocks germinate normally; the mycelium at the growing tips is basically normal, though its density and whiteness are slightly poor.

Actual examination: the moisture content of the substrate is basically suitable; the surface mycelium is sparse; oyster mushroom mycelium can be seen by experience, but it is very thin and weak and small in amount; when the mushroom bag is opened, there is an obvious undesirable gas, a rather pungent mixed smell of acridity, spiciness and rot; the mycelium inside the bag is sparse, but there is clearly mycelium connecting it, causing the substrate to clump, though rather loosely; and factors such as chemical reactions were ruled out.

In numerous telephone consultations, mushroom farmers mostly suspected nematode damage. Actual examination: no nematodes were found under microscopy, nor were mushroom fly larvae, mites or other pests found, and based on analysis of the mycelial condition, pest damage was ruled out; observation of several typical mushroom bags showed that apart from a few spots of Trichoderma and Aspergillus, no large-scale contamination was found in production; but after “mycelial regression” has persisted for a period of time, miscellaneous fungi such as Trichoderma will quickly colonize the substrate surface.

Diagnosis: the main cause is poor ventilation in the mycelial running shed, as heat preservation leads to an elevated carbon dioxide concentration inside the mushroom shed; secondary causes are insufficient nutrition in the substrate and aging of the spawn.

Treatment methods: open the ventilation holes of the mycelial running shed to ventilate it; use a steel rod 12 mm in diameter to punch 2-4 longitudinal holes in each mushroom bag, withdrawing the steel rod while rotating to keep the holes open; punch micro-holes all over the mushroom bags, about 30 per bag, by simply piercing the plastic film directly with a toothpick; try to raise the temperature of the mycelial running shed to about 20°C; after mushrooms appear, spray with Sanwei Jingsu.

Results: after the affected mushroom bags were treated as above, mycelial running resumed within one week, the mycelium was pure white and in good condition, the areas of mycelial regression were covered with dense new mycelium, and after half a month all produced mushrooms normally.

In response to the above mycelial regression problem, special suggestions for mushroom farmers: before production, carry out effective testing of the spawn and raw materials, with virus elimination of the spawn being one of the key points; the substrate requires a scientifically designed formula, with the addition of the edible mushroom three-dimensional nutrient essence, so that it is rich and balanced in nutrition, laying an appropriate material foundation for the robustness of oyster mushroom mycelium and the improvement of its resistance. Strengthen disinfection and treatment of the mushroom shed and contaminated mushroom bags, punch longitudinal holes in mushroom bags where mycelial regression has occurred and add more micro-holes, appropriately raise the temperature inside the shed and lower the humidity so that the mycelium can resume growth as quickly as possible; according to local environmental conditions, during the mycelial running period spray a solution of Baibing Quwuzong or Saibai 09 once every 3-7 days to ensure smooth progress of mycelial running.