What Causes Deformed Oyster Mushrooms? Detailed Explanation of Causes and Control Methods
Oyster mushroom (scientific name: Pleurotus ostreatus; also known as the oyster mushroom, brown-blewit oyster mushroom, oyster cap, black peony mushroom, and in Taiwan, China also called Xiuzhen mushroom) is a species in the family Pleurotaceae, order Agaricales, class Basidiomycota. It is a fairly common grey edible mushroom. Traditional Chinese medicine considers the oyster mushroom warm in nature and sweet in taste. It has the effects of dispelling wind and cold and relaxing the muscles and activating the collaterals. It is used to treat ailments such as waist and leg pain, numbness of the hands and feet, and blocked collaterals. The proteoglycans in oyster mushrooms have a strong inhibitory effect on cancer cells and can enhance the body's immune function.
Environmental requirements of oyster mushrooms
1. Nutrition. Oyster mushrooms can use many nutrients; both woody plant residues and fibrous plant residues can be utilized. In artificial cultivation, waste cotton, cottonseed hulls, corncobs, cotton stalks, and soybean straw give relatively high yields in that order, and other agricultural and forestry wastes can also be used, such as sawdust, rice straw, wheat straw, and corncobs.
2. Temperature. The mycelial growth temperature range and optimum temperature are not exactly the same for different species; most species and cultivars can grow at 5-35°C, and 20-30°C is the common suitable temperature range for their growth. The optimum growth temperature for low-temperature and medium-low-temperature cultivars is 24-26°C, the optimum growth temperature for medium-high-temperature and wide-temperature cultivars is about 28°C, and the optimum growth temperature for the Phoenix mushroom is 25-27°C.
3. Humidity. The optimum substrate moisture content for mycelial growth is 60%-65%. When the substrate moisture content is insufficient, colonization is slow, and fruiting is delayed after colonization is complete. In raw-material cultivation, when the substrate moisture content is too high, air permeability is poor, mycelial growth is slow, and anaerobic bacteria or molds are prone to grow. During the fruiting period, 70%-75% is optimal. When the atmospheric relative humidity is 85%-95%, the fruiting bodies grow rapidly and vigorously; below 80%, the caps tend to dry at the edges or crack; and if it exceeds 95% for a relatively long time, mushrooms are prone to rot. In raw-material cultivation, the method of keeping colonization on the dry side and replenishing water during the fruiting period is often adopted to ensure that the colonization period is not infected by molds and to ensure sufficient moisture during the fruiting period for fruiting.
4. Air. Oyster mushrooms are aerobic fungi. The mycelium can grow normally under plastic film cover, and can also grow normally in spawn bottles sealed with plastic film. Under a certain carbon dioxide concentration, the mycelium grows better than under the normal carbon dioxide content in natural air. That is to say, a certain concentration of carbon monoxide can stimulate the growth of oyster mushroom mycelium, but the formation, differentiation, and development of fruiting bodies require sufficient oxygen. When oxygen is insufficient and the carbon dioxide concentration is too high, fruiting bodies are not easily formed.
5. Light. The mycelium of oyster mushrooms does not need light for growth; light instead inhibits mycelial growth. Therefore, a dark or low-light environment should be provided during the colonization period. However, the occurrence or growth of fruiting bodies requires light, especially the formation of fruiting body primordia. In addition, light intensity also affects the color of the fruiting bodies and the length of the stipe. By comparison, under stronger light conditions, the fruiting bodies have darker color, shorter stipes, thicker flesh, and better quality; when light is insufficient, the fruiting bodies have lighter color, longer stipes, thinner flesh, and poorer quality.
6. pH value. Oyster mushroom mycelium can grow within a pH range of 3.5-9.0, with a suitable pH of 5.4-7.5. In cultivation, after natural compost and natural water are mixed, the substrate pH is mostly 6.0-7.5, which is just suitable for oyster mushroom mycelial growth. However, in actual cultivation, quicklime is often added to raise the pH to 7.5-8.5 in order to inhibit molds and their growth and ensure colonization.
7. Others. During the growth and development of oyster mushroom fruiting bodies, they are sensitive to harmful gases in the air such as carbon monoxide, sulfides, and acetylene. When the concentrations of these substances in the air are relatively high, the fruiting bodies stop growing, become deformed, or even wither. In addition, they are also allergic to dichlorvos; after using dichlorvos to kill insects in the mushroom house, the fruiting bodies curl upward to form "chicken-claw mushrooms."
Causes of deformed oyster mushrooms and their control
Deformed mushrooms are a relatively common physiological disease in oyster mushroom production, seriously affecting the yield and quality of oyster mushrooms, and even causing them to completely lose commercial value. This disease is mainly caused by improper management, and in a few cases by spawn degeneration, mutation, or viral infection.
The main types of deformed mushrooms are: 1. Long-stipe mushroom: the cap is small, differentiation is relatively poor, and the stipe is relatively long. The cause is that during the primordium formation and differentiation stage, the mushroom house is short of oxygen, light is insufficient, and at the same time the temperature is relatively high, which affects the normal differentiation and development of the cap. Control method: strengthen ventilation, and adjust light and temperature. 2. Tumor-cap mushroom: the cap shows mainly many granular protrusions at the edge, light color, stiff cap, and slow growth; in severe cases, the cap differentiates poorly and has an irregular shape. The cause is that the temperature during fruiting body development is too low and lasts for a relatively long time, causing disordered growth of the inner and outer cell layers. Control method: adjust the mushroom house temperature to above the minimum temperature limit for oyster mushroom growth, and maintain a certain temperature difference to promote fruiting body growth, development, and differentiation. 3. Cauliflower mushroom: the mushroom body resembles cauliflower, with many branches; in the early stage the primordium is egg-shaped, swells, bulges, and does not differentiate. In the later stage it has many branches. The cause is that before or during fruiting, a high-concentration pesticide, especially "dichlorvos," was sprayed on the mushroom bed or in the mushroom house; young mushrooms are extremely sensitive and most easily develop this disease. It may also be that the mushroom house contains other harmful gases, such as an excessively high carbon dioxide concentration or sulfur dioxide released by coal burning. Control method: use pesticides cautiously in the mushroom house, and do not use them at too high a concentration. In particular, dichlorvos must absolutely not be used during the fruiting period; strengthen ventilation and air exchange to discharge harmful gases. 4. Shriveled mushroom: the mushroom body is normal at first, but during the expansion period it turns yellow, becomes water-soaked or shriveled, stops growing, and finally softens and rots. The water-soaked condition is caused by excessive humidity or too much water sprayed directly on young mushroom bodies, causing the mushroom tissue to absorb water, affecting respiration and metabolism, and thus stopping growth and dying. The shriveled condition is caused by relatively low atmospheric relative humidity, excessively strong ventilation, or wind blowing directly on the mushroom bodies, causing oyster mushrooms to lose water and die. Or it may be caused by nutritional imbalance in the culture medium: after a large number of primordia form, some grow rapidly while the rest stagnate due to insufficient nutrient supply. Control measures: control humidity between 80-85%, do not spray water on young mushroom bodies, and do not let wind blow directly on the mushroom bodies. Reasonably match the composition of the culture material. A small number of shriveled mushrooms are caused by spawn degeneration; the symptoms are that the cap curls back, turns yellow, and shrivels before it has grown large enough. Control method: select excellent cultivars. 5. Coral mushroom: the primordium differentiates abnormally, is loose, and has many fine branches, resembling coral in shape. The cause is that when the primordium forms, ventilation is seriously poor, light is extremely weak, and the nitrogen source is lacking. Control: strengthen ventilation and light regulation, adjust the carbon-to-nitrogen ratio, and add a nitrogen source.