By Umar Nsubuga
Many years ago, mushrooms were considered to be wild plants, although most of these spore-producing bodies of fungi are inedible, field mushrooms are.
Many people still doubt that mushrooms can be cultivated because of their mysterious form of propagation, but Sheila Kanyarusoke, a resident of Isanga village, Bulingo parish in Kyegegwa district, sees gold.
She says mushroom species grown in the tropics, any farmer needs small space and relatively modest capital input.
“Such a project could be carried out in one’s house. There are over 39 species of mushrooms that thrive well in the tropics. Some of the varieties include Pleurotus (Oyster), Volvariella, Lentinus, Auricularia, Coprinus Cinereus and Agaricus bitorquis species. Other subspecies include; P.ostreatus, P.sajor caju, P.flabellatus and P.eryngii,” she says.
Pleurotus species can be found on wood in deciduous and coniferous forests.
Deborah Gitta, a regular farmer in Mpererwe says mushroom production involves various techniques at different stages.
“There is substrate pasteurisation, spawn running and initiation for fructification and cropping,” she says.
Materials used as substrates
According to Kanyarusoke, an organic material known as substrate is the medium through which the cultivated mycelium (spawn) grows.
She says substrates include cotton husks, hay, maize cobs, straws, millet, sorghum, rye, coffee pulp, used tea leaves, wheat, dry bananas, sugar cane bagasse, sawdust and tree logs.
Pasteurisation of substrates
The substrates must be dry and intact before pasteurisation. They must not decompose whatsoever.
The composition of a substrate and the environment determines which fungi and microbe grow well on it.
Kanyarusoke says a good substrate provides good anchorage to the fungus and has the right water-holding capacity and good compactness.
“Some fungi can use a broad range of substrates, while others are very selective. If a substrate is too tight or loose; the spawn will have difficulty colonising it,” Kanyarusoke explains.
For instance, the spawn cannot breathe in a tight substrate. If it is too loose, the spawn needs more energy to reach the next bit of sawdust or straw.
Gitta says oyster mushrooms are usually grown on pasteurised substrates of different types. The spawned pasteurised substrates are packed in plastic bags and compressed.
Holes for air circulation are aseptically made on the bags and placed in a cropping room for spawn running.
Certain species of mushrooms need fermented substrates for suitable growth. If fresh substrates are used, Gitta says the heat generated by microbial activity resulting from the decomposition of easily degradable matter will kill the mycelium.
Fermentation gets rid of easily accessible components making the substrate stable, treated with heat and spawned.
Kanyarusoke says the treatment makes it optimal and selective for the desired mushroom and not other, fungi.
Heat treatment such as sterilisation under high/low pressure and pasteurisation by steam or immersion in hot water is crucial for both fermented and unfermented substrates to control pests and diseases.
Sustained hot water treatment of 60 to 70 degrees centigrade kills unwanted organisms and keeps the favourable ones alive.
“Most pathogens will be eliminated at this temperature. Substrates such as hay, bagasse and straws must be chopped into small pieces of about 3cm- 5cm long before the heat treatment”, she advises.
She adds, “They must then be packed in wire baskets or nylon bags and immersed in hot water of about 80 degrees centigrade for about an hour. Daily watering of substrates must be done hygienically with boiled water that has been kept in clean containers when cooling.”
The watering should not be excessive to cause waterlogging. After an hour of pasteurisation, the substrates are drained off of all hot water and taken to the spawning room.
They are spread on clean plastic sheets and allowed to cool at room temperature after which they are spawned. Oyster mushroom clusters growing in the substrate lump or garden.
Spawn making and spawning running
Kanyarusoke says that spawn is a collection of mycelium of a mushroom on a carrier material.
She says it is the grain on which the mycelium grows; the actual seeding material or planting of mushrooms. The spawn used in this class comes from rye berries from a commercial spawn producer.
Mycelium is the true mushroom “plant.” The part you eat is the fruit, often referred to as the fruit body.
“Hygiene is very important in the spawning and cropping rooms of a mushroom farmhouse. These two rooms must have a double-door entrance and the farmer must be adorned in special shoes and clothes while inside,” she explains.
Before spawning, it is advised to lump the pasteurised substrate into 5kg-1Okg gardens. At this point, the l00g spawn can be inoculated onto the pasteurised substrate. Inoculation is the mixing of the substrate with the -spawn.
When the mushroom mycelium has been completely colonised by the substrate in 14-17 days after spawning, Gitta says slits should be made on the plastic bags using a clean knife or six-inch-size nail preferably heat-sterilised. About 24 holes can be punctured into the bags for mushroom hyphae to breathe easily and grow well. Failure to do so kills the spawn.
Spawned substrates should be kept in the dark “spawn room” for proper growth of mycelium until fully colonised, then moved into the growing room.
Humidity, ventilation, shade and the sun must all be balanced for mushrooms to thrive. Good ventilation should be provided by constructing one window higher than the one on the opposite side.
Kanyarusoke says humidity can also be kept by either spraying, using a humidifier or sprinkling the cement floor with water.
She also says a wide pan of water must be permanently kept in the running room. Appropriate environmental factors must be observed for better growth of mushrooms.
For instance, the nominal temperature should be between 700 C and 800 C.
Fructification (cropping)
“High humidity is paramount during the fruiting cycle because the lumps need a warm area since mushrooms sprout shortly after this. Spraying (mist) must be done several times a day, J cautiously noting that if the developing mushrooms start turning brown, more humidity is required”, Kanyarusoke says.
When the mushroom begins to form through the nail holes, ‘the largest first fruiting called “flush” will emerge.
Oyster mushrooms are easy to cultivate because they grow through holes in the lumps and quickly form clusters ready for harvest.
When the stalks sprout, Kanyarusoke says plenty of light should be allowed into the cropping room for it to form caps known as “mushroom fruit bodies” which require appropriate temperatures of 25-28 degrees centigrade, sufficient ventilation, light, moisture and relative humidity, 80 – 90 per cent in warm tropical countries.
On average, each lump produces about 2.5kg of oyster mushrooms depending on environmental conditions. Poor strains used to prepare spawns, unsuitable substrates, wrong temperature, lack of moisture or relative humidity and pests and diseases affect mushroom yields.
Expanded metal or wire mesh/gauze and black cloth or plastic sheets should be put on the windows to keep the room dark while keeping rats and flies out.
