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:
Plastic bags:
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.
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. |