Shiitake Mushroom

(Lentinula deodes)

It is known as "shiitake" in Japan. Origin of this mushroom is China. The shiitake mushroom grows on old wood from dead residues of trees. Various hardwood species of trees have been used in the bed log production of shitake. The name Shii-take was due to one of the primary species shiitree used in one area of Japan in the past. Most of the production today, however, is on various species of oak.

Preparation of wood-piece spawn:

Bed logs are usually cut after the leaves fall in the autumn. Trees cut in the summer tend to have loose bark that may strip off more easily, increasing the possibility of contamination. Wood-piece spawn is prepared by cutting small cylindrical pieces of wood of about the same size (3 cm x 3 cm) as the holes drilled in the logs into which they will be planted. The wood pieces are first soaked overnight in plain water or nutrient solution, they are later drained and placed in bottles or jars and are sterilized for at least one hour. After cooling, each bottle is inoculated with a mycelial plug of the mushroom and incubated until the wood pieces are fully permeated with the mycelium.

Inoculation:

After the logs have been cut to the desired size, holes are drilled in the logs corresponding to the size of the spawn pieces. Special drills with a stop collar to facilitate the hole-drilling process can be used for this purpose.

Holes drilled in a log are about 30 cm deep when parallel to the grain and about 10 cm deep when drilled perpendicular to the grain. They are staggered to provide more rapid colonization. The wood pieces are driven into the holes and are usually covered with hot wax to prevent drying. Sawdust spawn is sometimes used instead of wood piece spawn. After removal from the container, pieces of spawn are broken off and placed in the holes.

Incubation:

Spawn run (laying) may last from 6 to 18 months, depending on the tree species, log size, spawn cultivar, amount of spawn used, moisture temperature, and other variables. The spawn run period may be divided into two phases. The first phase lasts from 1 to 2 months. Often referred to as temporary laying, the freshly inoculated logs are frequently incubated vertically or horizontally in special stacks. For vertical incubation, 50 to 80 logs may be placed on end under a shade canopy, touching each other, and laying on a plastic sheet or dry straw.

For horizontal incubation, the log may be closely stacked together (1 m high) on two non-inoculated logs which are placed at right angles to the stack. The two non-inoculated logs supporting the pile serve to prevent the logs from touching the ground and help minimize weed mold and other pest infestations. After 1 or 2 months, the logs are destacked and moved to a more permanent location. Destacking is needed because the condition created within the stacks favour the development of competitive weed molds.

Design of mushroom house:

The permanent laying yard should have environmental conditions that favour spawn run but not competitive weed molds. It requires optimum temperature between 18 to 27oC,a relative humidity between 50 to 70%, and moderate air circulation. To help maintain these conditions, optimum site selection and correct log stacking patterns are essential.

A sandy soil with good drainage is preferred. After the spawn run period, the logs are often transferred to a "raising" yard. This change in conditions provides a more optimum environment for the growth and development of mushrooms.

In the raising yard, the logs are arranged to provide for the convenient harvesting of the mushrooms. The x-frame is the most popular stacking pattern used in the raising yard and allows the developing mushrooms to mature without contacting an adjacent log. If the logs are placed horizontally, mushrooms, developing on the undersides of the logs are often mishappen and of lesser quality. Logs in the raising yard are sometimes turned end-to-end every 2 to 4 months to help equilibrate log moisture contents. Heat is supplied by burning spent shitake logs in furnace /air handling unit which is designed to distribute the heat as uniformly as possible.

 

During, or shortly after soaking, the logs, which remain in the soaking racks, are vibrated to help stimulate fruiting. Vibration helps to evacuate carbon dioxide entrapped in intracellualr and intercellular spaces. After soaking and vibrating, the logs may be returned to an empty soak tank and are covered for 4 to 6 days to help maintain a high humidity. They may be placed directly in a greenhouse where they are leaned against a rope-wrapped rail. Horizontal racking system are sometimes used in the greenhouse but they are less popular since they require more expensive racks and mushrooms emerging from the undersides of the logs may be mishappen.

Cultivation of Shiitake on Supplemented Sawdust:

  1. Plastic bags:

  2. The substrate usually comprises a mixture of wood chips, cereal bran and miller, and other mineral and vitamin supplements. Wood chips from hardwood species are usually preferred, although a small proportion of softwood species may be mixed with the hardwoods. A formula of sawdust (80%), wheat bran (10%) and miler (10%) can also be used.

    After mixing the dry ingredients by hand or with a mechanical mixer, water is added to the mixture so that the final moisture content of the substrate is between 55 and 68% depending on the capacity of the sawdust to absorb water. The ingredients are then packed into autoclavable polypropylene or high-density polyethylene bags. After the bags have been filled (1.5 to 4 kg wet wt.) the neck of the bag is fitted with a plastic collar and plugged with a cottonwool stopper. After filling the bags noncompacted or compacted nutrient supplemented sawdust, the substrate is heat-treated to kill unwanted competitive micro-organisms. Heat treatment maybe carried out in an auotclave at 121oC for 1hr or in a brick and cement-lined tower at 90-95oC for 5-7 hr.

    After cooling, the substrate is inoculated with spawn. Inoculation is usually performed in a laminar flow. Bags containing a breather strip are heat-sealed immediately after inoculation to prevent further exposure to nonfiltered air.

    Spawn run (the time required for the mycelium to colonize the substrate) may range for 18 to 100 days. During this period, the bags are usually incubated in a 4 hr /20 hr light /dark cycle at 23-25o C. The substrate may lose 5-10% of its dry weight and may subsequently have a higher moisture content. With longer spawn runs (over 40 days), the surface of the colonized substrate may being to turn brown; some exudates may be produced and drain to the bottom of the plastic bag. This is considered desirable. A longer spawn run usually results in a higher rate of production during the cropping cycle.

    At the end of the spawn run, the plastic bag is cut away and the synthetic logs are subjected to production conditions. The wood chips are held together by the fungal mycelium. Misting be provided daily by overhead nozzles controlled automatically. Relative humidity is often maintained at 95-98% during the periods when the nozzles are not in operation. Two hours of cool white light (50 lux) is usually provided and controlled automatically. An optimum temperature range 14-16oC is desirable for most of the lines of shiitake. Sufficient air changes in the room are maintained to hold CO2 levels below 1200 ppm. Mushroom usually begins to appear 7-10 days after placement in the production room and reach maturity 11-14 days after debagging.

  3. Straw

Some growers produce shiitake on a straw-and-wood chip mixture supplemented with feather meal. Benomyl is also added. The substrate undergoes high temperature pasteurization. Spawning rates are relatively high (5% of dry substrate weight) to overcome contamination with competing weed molds. Efficiencies are relatively low (16-20% over 4 to 6 months), but this method has the advantage of utilizing current Agaricus production facilities.


Ag.
Technologies
(Mushroom Cultivation)