Mushrooms

Description

Mushrooms are the fleshy fruiting bodies of fungi and include edible species in the genus Agaricus (button mushrooms, portabellas and criminis), Pleurotus (oyster mushrooms), and Volvariella, (straw mushrooms). Mushrooms are highly variable in appearance depending on their stage of development and variety. Agaricus mushrooms have a cap and stem, the cap is a pale grey or brown in color and is rounder while immature, but flattens out as it reaches maturity and can reach a diameter of 5–10 cm (2–4 in). Pleurotus mushrooms may not have a stem and instead may be laterally attached to a growing substrate such as the bark of a a tree. Pleurotus mushrooms are smooth and elongated and can reach 4–15 cm (1.5–6.0 in) in diameter. Volvariella mushrooms are small, with pink gills and a characteristic sac-like covering (volva) at the base of the stem. The cap can reach 5–15 cm (2–6 in) in diameter.


Uses

Mushrooms are widely used after cooking and are incorporated into many dishes worldwide.


Propagation


Basic requirements
Mushrooms grow from a filamentous mass (mycelia or 'spawn') that grows on dead or decaying plant material. Agaricus mushrooms can be cultivated in a dark, moist, cool space such as a basement. Agaricus mushrooms require a rich organic material in which to grow such as horse manure. Oyster mushrooms are cultivated on hardwood logs by introducing spawn into pre-drilled holes in the wood or or by sawing a section through the log and covering the exposed wood in spawn before nailing the log back together. The logs are then stored in watertight bags containing sand and soaked with water. Oyster mushrooms can also be grown in straw or sawdust by inoculating the sterile substrate with spawn and sealing in plastic bags. Straw mushrooms can be grown on wheat straw, rice straw or sawdust inoculated with spawn and stored at temperatures between 28 and 36°C and relative humidity of 75–85%.

Propagating Agaricus mushrooms

Substrate
Substrates for growing Agaricus mushrooms are either agricultural by-products such as straw bedded horse manure or synthetic composts specially formulated for mushroom growing. Horse manure substrates should have a nitrogen content of 1.5–1.7%, while synthetic composts should contain between 1.7 and 1.9%. Additional nitrogen can be added to the substrate if required using nitrogen supplements or through the addition of poultry manure. Gypsum is commonly added to the mix to buffer the pH and to give the compost the desired structure for optimum mushroom growth. The growing substrate then must be composted to make it suitable for growing mushrooms. Horse manure is composted by turning every 4–5 days and watering after each turning to keep the substrate moist. The compost is ready to use when it turns a rich brown color, usually after 4 or 5 turnings. Other compost mixes should be turned after 5–6 days and kept moist by watering. The compost should be turned a second time and should be ready for use after another week. the compost is then set out in trays for planting the spawn. In commercial mushroom production, the compost is pasteurized to remove and fungal, bacterial or insect contaminants from the medium before the spawn is planted.

Spawn
Mushroom spawn can be purchased from many commercial seed companies or online suppliers. Spawn should be planted when the compost reaches 24°C (75°F) and should be planted in the trays at a depth of 5 cm (2 in) allowing 20–25 cm (8–10 in) between plantings. The temperature should be kept at 21°C (70°F) for the next 21 days before lowering to 15.6°C (60°F) and covering with a 2.5 cm (1 in) layer of good quality soil. The growing mushrooms should be kept moist throughout by watering with a gentle spray of water whenever the top of the soil begins to dry. Tiny white spots should begin to appear on the soil surface after approximately 3 weeks and will begin to be ready for harvest approximately 10 days later.

Harvesting
Harvest the mushrooms at soil level by carefully twisting them or by cutting them at soil level with sharp knife. Pulling can damage other surrounding mushrooms. Harvest flushes of mushrooms daily. The beds will continue to produce for up to 6 months.


References

Beyer, D. M. (2003). Basic procedures for Agaricus mushroom growing. Penn State College of Agricultural Sciences. Agricultural Research and Cooperative Extension. Available at: http://pubs.cas.psu.edu/freepubs/pdfs.... [Accessed 24 February 15]. Free to access.


Common Pests and Diseases

Green mold
Trichoderma spp.
Penicillium cyclopium
Aspergillus
spp.

Symptoms
A dense layer of mycelium is present on casing surface which is initially white in color but changes to green; developing mushrooms in or near the mycelium are brown and may be cracked or distorted
Cause
Fungi
Comments
One of the most common and destructive diseases of cultivated mushrooms
Management
Prevention of disease is best achieved by following good sanitation practices; ensure compost is properly pasteurized prior to use and sterilize any supplements

Dactylium diseases
Dactylium cladobotryum

Symptoms
Webbed, cottony mycelial growth on surface of casing and mushrooms; mycelium is usually white but may be gray or pink in color; infected mushrooms will develop a soft, watery rot
Cause
Fungus
Comments
Growth of the mold is restricted to the casing layer; disease can spread very quickly if left untreated
Management
Control of the disease is achieved through good sanitation practices and cultural control methods; casing should be kept clean and sanitized; all tools and equipment should be cleaned and sanitized between use; keep beds free of any mushroom debris; pathogen in susceptible to low humidity and can be inhibited by lowering the humidity in the growing room

Verticillium spot
Verticillium fungicola

Symptoms
Small spotting on mushrooms; mushrooms deformed; surface of mushroom gray and fuzzy; localized dead areas on cap; pinched areas on cap; fruiting body may no longer be recognisable as a mushroom; severe infection can cause a deformation known as "dry bubble" which causes the sporocarp to appear as large puffball like masses; bubbles will become covered with a gray, fuzzy growth
Cause
Fungus
Comments
May be confused with bacterial infections; spread by flies and/or infected equipment
Management
Bubbles should not be disturbed by touching and can be destroyed using salt; salt should be placed in a plastic cup and then placed over the bubbles to dry them out and provide a barrier to prevent spores spreading; fungicides are available for the treatment of Verticullium diseases of mushrooms but many have toxic effects on the mushrooms as they are themselves a fungus