What are the control methods for competitive contaminant fungi in edible mushrooms

1. The harmfulness of competitive contaminant fungi in edible mushrooms

In the process of edible mushroom production, due to large-scale cultivation or production at the same site for many years, edible mushroom diseases, insect pests and contaminant fungi frequently occur, spread quickly and cause great losses, becoming a major obstacle to the development of edible mushroom production.

Among them, competitive contaminant fungi such as bacteria, Trichoderma, Mucor, Rhizopus, Aspergillus and Neurospora frequently occur, infect the mycelium of edible mushrooms, grow quickly, compete for the nutrients in the substrate, secrete toxins, inhibit the normal growth of the edible mushroom mycelium, and cause contamination of spawn and spawn bags, lowering the finished-product rate. Some competitive contaminant fungi also infect the fruiting bodies, causing diseases. Because of the infection by these competitive contaminant fungi, the contamination rate of spawn bags can reach 10%-20%, and in some cases as high as 30%, causing serious losses. In many cases, the degree of harm from competitive contaminant fungi has exceeded that from edible mushroom diseases and insect pests, becoming a major issue that must be seriously addressed in edible mushroom production.

2. Analysis of the causes of competitive contaminant fungi in edible mushrooms

The occurrence and spread of competitive contaminant fungi in edible mushrooms are caused by many factors. The main reasons are as follows.

2.1 Spawn contamination. During spawn production, careless operation causes contaminant fungi contamination. During the spawn culture period, if timely inspection is not carried out, the growth of the edible mushroom mycelium masks the contaminant fungi, and spawn carrying contaminant fungi is produced. Using this kind of spawn for subculturing will cause contamination of spawn bags in batches.

2.2 Many years of continuous cropping at the production site. In culture rooms and fruiting rooms with continuous cropping, contaminant fungi accumulate heavily and have not been thoroughly controlled, which most easily leads to contaminant fungi contamination of spawn bags.

2.3 Unreasonable substrate formulation. Excessive water content in the substrate or too much carbon source and too little nitrogen source during the mycelium-running period, causing an imbalanced carbon-to-nitrogen ratio, can easily lead to contaminant fungi infection.

2.4 Incomplete sterilization of the substrate. Edible mushroom spawn and cultivation substrates are mostly sterilized by heat steam. Sterilization requires reaching a certain temperature and pressure and maintaining them for a certain time. If the standards required by the technical specifications are not met, the substrate will not be thoroughly sterilized, contaminant fungi will remain in the substrate, and under suitable conditions the contaminant fungi will grow out and contaminate the spawn bags.

2.5 Contamination during inoculation. When subculturing spawn and spawn bags, if the inoculation room (or inoculation box, inoculation tent) has not been disinfected or has not been thoroughly disinfected, the environment carries microorganisms, and aseptic technique is not used, contaminant fungi enter the spawn bottles or spawn bags along with the inoculation, grow and multiply, and cause contamination.

2.6 Contamination during the culture period. Contamination of spawn bags during the culture period, in addition to the above reasons, is also closely related to the thickness and quality of the spawn bags, the environmental conditions of the culture room, and whether the culture room has been disinfected.

Poor-quality spawn bags with micropores allow contaminant fungi to enter through the micropores, which is one of the main causes of spawn bag contamination. A culture room without ventilation, with high temperature and high humidity, very easily causes contamination. If bags are turned few times during the culture period and contaminated spawn bags are not eliminated in time, cross-contamination by contaminant fungi easily occurs.

If the culture room has been used for many years, contaminant fungi accumulate heavily and no chemical control has been carried out, the spawn bags are very easily infected by contaminant fungi.

2.7 Contamination during the fruiting period. If the mushroom house has not been disinfected and sterilized with chemicals, and is also hot and humid, the spawn bags are easily contaminated. This is especially true for old mushroom houses.

2.8 Differences in disease resistance among varieties. Different varieties differ to some extent in disease resistance; for example, Beijing large wood ear is more resistant to contaminant fungi contamination than other black wood ear varieties.

3. Integrated control of competitive contaminant fungi in edible mushrooms

Competitive contaminant fungi in edible mushrooms should be controlled according to the principle of prevention first and integrated control. Before contaminant fungi infect, integrated preventive measures should be taken so that they do not occur or infect only slightly. If large-scale contamination has already occurred, then control will be relatively difficult.

The main measures of prevention first and integrated control are as follows.

3.1 Select excellent varieties with disease resistance, contaminant resistance and high yield.

3.2 Ensure that the spawn is pure. This is the prerequisite for pure culture of edible mushroom mycelium. Throughout the entire spawn production process, aseptic technique must be used. The inoculation room and inoculation tools must be disinfected. Turn on the ultraviolet lamp for half an hour for sterilization, and also spray chemicals or fumigate with chemicals to ensure that the inoculation environment does not carry microorganisms. During inoculation, operate in the sterile zone above the flame of an alcohol lamp.

Fumigating the inoculation room (inoculation box, inoculation tent) with Bijieshi brand compound disinfectant (chlorine dioxide) is one option. Bijieshi brand compound disinfectant can be widely used for disinfection of inoculation rooms, inoculation tents, inoculation boxes, culture rooms and fruiting rooms.

During the spawn culture period, inspections must be carried out frequently, and contaminated spawn must be eliminated at any time. During the culture period of first-level spawn, inspect 2 times; for second-level and third-level spawn, inspect 2-3 times.

Attention should be paid to spawn age. For spawn used for production and subculturing, first-level spawn is best used within 1 month of storage, and second-level and third-level spawn are best used within 20 days of storage. The longer the spawn age, the greater the probability of contamination.

3.3 Select a cultivation substrate formula with a reasonable carbon-to-nitrogen ratio. For example, during the mycelium culture period, the C/N ratios of the main mushroom species are: button mushroom 17:1; oyster mushroom, straw mushroom and black wood ear 20:1; enoki mushroom 20-25:1; lion's mane mushroom 25:1; shiitake 25-30:1. During the fruiting period, the carbon source should be increased for each mushroom species. The suitable water content of the cultivation substrate is 60%, and the substrate-to-water ratio is 1:1.1-1.2.

3.4 The substrate must be thoroughly sterilized. With normal-pressure sterilization (100°C), 10-16 hours are needed, or longer. With high-pressure sterilization, the pressure should reach 126°C and be maintained for 2-4 hours.

3.5 Management during the culture period of spawn and spawn bags. The culture room and culture workshop must be fumigated with chlorine dioxide compound disinfectant for 4 hours, using 0.3 grams per square meter for fumigation, with the chemical placed at a height of 50 cm-80 cm; the relative air humidity must be higher than 50%, and dark and sealed conditions must be maintained. Fumigating again the next day can achieve twice the result with half the effort.

During the culture period, the temperature of the culture room (culture workshop) should be controlled at 20-24°C;

the relative air humidity should be maintained at 30%-60%, with frequent ventilation and air exchange, and dark culture. During the culture period, inspect the spawn or turn the bags 2-3 times, and promptly eliminate contaminated spawn and spawn bags. Some production units use the double-bag method, greatly reducing the contamination rate.

3.6 Management during the fruiting period. Before using the mushroom house, fumigate it with chlorine dioxide compound disinfectant, using the same method as above. Cover with straw curtains and fumigate away from light. For old mushroom houses, increase the dosage to 0.4-0.5 grams per square meter.

During the fruiting period, according to the growth needs of different mushroom species, manage carefully and maintain suitable temperature, relative humidity, scattered light and ventilation conditions.