[ Dr Nitin Kumar Pandey ]
ITANAGAR, Aug 31: The oyster mushroom is one of the most suitable fungal organism for producing protein rich food from various agro wastes without composting. The mushroom is cultivated in about 25 countries of Far- East Asia, Europe and America. It is the third largest cultivated mushroom in the world. China alone contributed 88 per cent of the total world production. The other major oyster producing countries are Japan, Italy, Thailand, Taiwan, South Korea and Philippines. In India, it is popularly grown in the states of Orissa, Maharashtra, Karnataka, Andhra Pradesh, West Bengal and the North- Eastern states.
Nutritional and medicinal value of oyster mushroom: This mushroom is 100 per centvegetarian and the nutritive value of oyster mushroom is a good as other edible mushrooms, like white button mushroom, shitake or paddy straw mushroom. They are rich in vitamin C and B complex. Protein content varies between 1.6 to 2.5 on fresh weight basis. It has most of the mineral salts required by the human body, such as potassium, sodium, phosphorus, iron and calcium. The niacin content is about ten times higher than any other vegetables. A polycyclic aromatic compound pleurotin has been isolated from P.griseus, which possess antibiotic properties.
Varieties: All the varieties of oyster are dibble expect P.nidiformis and P.olearius, which are reported to be poisonous. In recent years, 25 species are commercially cultivated in different parts of the world, which are: P. florida, P. flabellatus, P.ostreatus, P. sajor-caju, P. sapidusetc.
Cultivation: The procedure for oyster mushroom of spawn. Cultivation can be divided into following four steps.
Preparation or procurement: Substrate preparation; spawning: Crop management; preparation or procurement: The spawn preparation technique for oyster mushroom is a similar to white button mushroom.
One should have a pure culture of pleurotusspp for inoculation on sterilized wheat grains. It takes 10 to 15 days for mycelia growth on grains. It has been reported that jowar and bajragrains are superior over wheat grains. The mycelium of oyster mushroom grows very fast on wheat grains and 25 to 30 days old spawn starts forming fruit bodies in the bottle itself.
Substrate preparation: Different type of agricultural, forest and agro-industrial by- products, are useful for growing oyster mushroom. These by products or wastes are rich in cellulose, lignin and hemicellulose. However, yield of oyster mushroom largely depends upon the nutrition and nature of the substrate.
Method of the substrate preparation: The mycelium of pleurotus is saprophytic in nature and it does not require selective substrate for its growth. The popular methods of substrate preparation are as follows:
Steam pasteurization: In this method prewetted straw is packed in wooden trays or boxes and then kept in a pasteurization room at 58-62 0C for four hours. Temperature of the pasteurization room is manipulated with the help of steam through a boiler. Substrate after cooling at a room temperature is seeded with spawn. The entire process takes around 3-5 days. This method is adopted on a commercial scale.
Hot Water treatment: The substrate (wheat straw) after chopping around 5-10 cm is soaked in hot water (65-700C) for one to two hour or in case of paddy straw at 85 0C for 45-55 minutes. After draining excess water and cooling, spawn is added. Hot water treatment makes the hard substrate like maize cobs, stems, etc soft so that the growth of mycelial takes place easily. This method is not suitable for commercial cultivation.
Chemical Treatment: Different species of trichoderma, Penicillium, Aspergillus and Gliocladium are the common competitor fungi on the straw during oyster mushroom cultivation. Ninety litres of waters is taken in a rust proof drum or G.I. tub of 200 litre capacity. Ten to twelve Kg of wheat straw is slowly steeped in water. In other plastic bucket, Bavistin 7.5 g and 125 ml formaldehyde is dissolved and slowly poured on the already soaked straw. Straw is pressed and covered with a polythene sheet. After 15-18 hour the straw taken out and excess water drained.
Spawning: The spawning should be done in a pre-fumigated room with 2% formaldehyde for 48 hour. 20 30 days old spawn is best for spawning. The spawn should be mixed @ 2 to 3 % of the wet weight of the substrate. 10 to 12 kg of wet substrate or 2.7 to 3 kg of dry substrate is sufficient for 300 g spawn. Spawn can be mixed thoroughly or mixed in layers. Spawn substrate is filled in polythene bags (60×45 cm) of 125 to 150 gauze thickness. 10 to 14 small holes (0.5-1.0 cm diameter) should be made on all sides especially in the bottom for leaching of excess water. Perforated bags higher and early crop (5-6 days) than non-perforated bags because of accumulation of high CO2, which inhibits fruiting. One can also use empty fruit packing cartoon or wooden boxes for filling substrate. The polythene sheet is folded from all the four sides to make a compact rectangular box. It is tightly pressed and tied with a nylon rope. The block is incubated as such and after mycelial growth polythene sheet is removed.
Crop Management: The spawn bags or blocks are kept in incubation room for mycelialgrowth. Spawned bags can be kept on a raised platform or can be hanged in cropping room for mycelial colonization of the substrate. Mycelium can grow between 10-30 0C but optimum temperature lies between 22 to 26°C. The temperature more than 30° C in the cropping room will inhibit the growth and kill the mycelium. During mycelia growth the bag are not to be opened and no vitalization is needed. Moreover, there is no needed for any high relative humidity, so no water should be spread. All the plutorius species require high relative humidity (75-85%) during fruiting. To maintain relative humidity, water spraying is to be done in cropping rooms. During hot and dry weather conditions daily 2-3 spray are recommended while in hot and humid conditions one light spray will be sufficient.
Post-Harvest Management: Mushroom should always be harvested before water spray. The right stage of picking can be identified by the shape and size of fruit body. In, young mushrooms, the edge of the cap is thick and cap margin is enrolled while the cap of mature mushroom is flat and inward curling starts. It is advisable to harvest all the mushrooms at one time from a bag so that a next crop of mushroom starts early. After harvesting lower portion of the stalk, adhering debris should be cut with a knife. Fresh mushrooms should be packed in perforated polythene bags for marketing. The can also be sun dried by spreading on a cotton cloth in bright sun light or diffused light. The dried produced with 2-4% moisture can be stored for 3 to 4 months after proper sealing.(The writer is Krishi Vigyan Kendra, Tawang, SMS Agri Extension)
