- Spawn production / procurement,
- Compost preparation,
- Spawning and spawn running,
- Environment control,
- Pests and disease control,
- Harvesting, grading and storage,
- Mechanization and
- Computer control.
The fungal bodies (mycelia) along with the medium of growth (cereal grains), which are used as planting material / seed for the production of mushrooms, are known as spawn. Spawn production is a highly specialized activity. It is produced from fruiting culture / stocks of selected strains (races or varieties of mushrooms) under sterile conditions. The strains vary in yield, flavor, texture, fruiting time etc. The strains which are being cultivated in India include S-11, TM-79 and recent strain, Horst U3.
Stock culture can be obtained from a reliable source or produced in the laboratory by single spore culture / multiple spore culture / tissue culture technique. many export oriented units import fruiting culture, which reportedly give higher yield than India strains, and produce the spawn in their own laboratory. A few units even import spawn directly from foreign sources.
A good spawn should have potential for high yield and good quality (flavour, texture, size). It should be free from contamination and have good survival in storage.
Mushroom need nutrients such as carbon compounds, nitrogen source, minerals, trace elements, vitamins and water. Button mushroom draws its sustenance for growth, development and fruiting from compost which meets its nutritional requirement. In other words, compost is the substrate (medium) on which button mushroom grows. It is prepared from a mixture of plant wastes (cereal straw / sugarcane bagasse etc.), salts (urea, super phosphate / gypsum etc.), supplements (rice bran / wheat bran etc.) and of course water. According to a suggestion, each ton of compost should contain 6.6 kg nitrogen, 2.0 kg phosphate and 5.0 kg potassium, which gives and N:P:K ratio of 33:10:25 and converts to 1.98% N, 062%P and 15%K on a dry weight basis. This ratio can be used as a guide while selecting the composition of the mixture for compost. The carbon: nitrogen ratio of 25-30:1 at the time of staking and 16-17:1 in the final compost may be considered as a good substrate. It has been estimated that to produce one kg of mushrooms, 220 g of dry substrate material are required.
The compost, technically a complex Lignocelluloses material, is the product of microbe mediated fermentation process, known as composting. For achieving high productivity of button mushroom, the compost needs to be pasteurized so as to kill undesirable microbes and competitors of button mushroom and to convert ammonia into microbial protein.
The compost for button mushroom should finally be free from ammonia, insects and nematodes, contain 70% moisture, should have dark brown color, sweet unobnoxious small, a pH of about 7.5 and granular structure.
Spawning The pasteurized compost is taken either in polythene bags or shelves (made of steel or RC) or trays. Polythene bags (90 cm x 60 cm, 150 gauge thick) which contain about 25 kg compost per bag can be placed on shelves. Trays are expensive. Beds can also be directly prepared on shelves by applying compost about 100-105 kg / M2 pressed to about 20 cm thickness. Spawning is the planting (inoculation) of the spawn into the compost. The spawn is mixed through the whole mass of compost at the rate of 7.5 ml / kg compost or 500 to 750 g/100 kg compost (0.5 to 0.75%). Thereafter, the fungal bodies grow out from the spawn and take about two weeks to permeate (colonize) the entire mass of compost-the process is known as spawn running.
On completion of the spawn run, the compost is uniformly covered with an unpacked shallow layer, 3-4 cm thickness of casing soil. The process is called casing. It is necessary to induce the initiation of fruiting primordia, to support growth and development of fruiting bodies (mushroom), to provide it anchorage, to promote growth of desirable mycelia, to prevent drying up of top layer of the compost and to regulate water exchange.
The desirable characteristics of the casing material include neutral to alkaline reaction (pH 7.0 to 7.5) high water holding capacity, stable and crumbly structure, absence of heavy and toxic metals and deficiency of nutrients. Peat moss mixed with ground limestone is preferred casing material. However, it is not available in India. A mixture of FYM and loam soil could be used. It needs to be sterilized before use.
Fruitification The promotion of Fruitification i.e., the formation of fruiting bodies, which ensures high yield of mushroom, is the ultimate goal of mushroom cultivation. For a week after casing, the growth of fungal bodies is continued. Thereafter, by manipulation of the environment the initiation of fruiting is encouraged. Fruiting of button mushrooms occurs as flush at weekly intervals. The first pick or flush takes about three weeks to appear after casing. Watering of beds at the rate of 1 litre per kg of mushroom picked is done. The first three flushes account for about 75% of the total yield. Picking may be continued up to fourth flushes, thereafter it may not be economic.
In modern mushroom growing, environment control has assumed a great deal of importance. It is essential to achieve high productivity and quality. At almost every state of mushroom growing, spawn production, compost making, spawn running, fruiting, cropping, storage of mushrooms, the environment control could lead to better results. The factors which are needed to be controlled are temperature, humidity, aeration, CO2 concentration, pH, and light. Their specific requirement varies according to the stages.
Pest and disease control
Button mushroom is vulnerable to many pests and disease. Ideally, their incidence should be prevented by appropriate hygienic measures, which include sanitation, disinfection, use of good quality spawn and pasteurized compost, maintenance of optimum environment, filtration of air (which does not permit entry of anything above 2 micron size into growing houses), scientific growing, proper disposal of spent compost, segregation of infected materials etc. Fumigation of growing rooms with methyl bromide with proper precaution (toxic to human beings) could be practiced. Formalin may be used for disinfection of shelves, rooms, equipments etc. Spraying pesticides and fungicides may be undertaken as a last resort.
Harvesting, grading and storage
Button mushroom may be harvested holding the cap between thumb and forefingers and upward twisting movement from left to right.The stage of harvesting of button mushroom is influenced by the grades used in marketing, which mainly buttons., caps and opens.Button mushrooms are highly perishable. They can be stored for 3-4 days at 4-5oC in polyethylene bags.
The large sized mushroom growing units, specially in the West, are highly mechanized. Compost turner, compost filling line, conveyer, spawn application machine, ruffler, tunnel filling machine, environment control, fumigation, disinfection, picking line and grading are all mechanized activities.
The yield of button mushroom depends on the following factors :
- environment in the growing house,
- casing material and
- crop management practices
The mushroom yield is expressed either in terms of kg per square meter or as kg mushroom per 100 kg of compost at filling. It can also be expressed as kg mushroom per 100 kg of dry organic matter of substrate.
Under sub-optimal management conditions, yield could be 8-10 kg per 100 kg compost or per M2 (assuming 100 kg compost per M2).
Irish farms are reportedly harvesting yield of 30-40 kg per M2. However, in the developed countries, yield of 23-26 kg per M2 is common. A few large farms in India have harvested yield of 16-18 kg per M2.
High moisture content (90%) and absence of protective cover render mushroom perishable. Deterioration (loss or moisture, respiration, oxidation, browning etc.) under normal conditions start almost immediately after harvest. Therefore, processing of mushrooms is essential for export. There are mainly four methods of processing buttoning mushrooms - drying, freeze drying and canning.
Dehydration at 67-700C is very slow and retains about 12% moisture. The cost is low, but the quality of end product is not high. The product may have a shelf life of 2-3 months. Freezing at - 25 oC can give the product a shelf life of 2-3 months.