Mushroom Spawn Preparation 

(A). Definitions of spawn and spawning. The word “spawn” is derived from an old French verb,  espandre, meaning to spread out or expand, which was derived from the Latin, expandere, meaning to spread. Spawn is also defined by Webster’s Dictionary as “the mycelium of fungi, especially of mushrooms grown to be eaten, used for propagation”. In the mushroom industry, spawn is a substrate into which a mushroom mycelium has impregnated and developed, and which will be used as a seed in propagation for mushroom production. In addition the verb, to spawn, is used to mean inoculation of a substrate with mushroom spawn.  The simple definition of spawning is the planting of mushroom spawn in the prepared  compost/substrate. Along with advances in spawn making, the methods of spawning have also been continuously developed and improved, making it possible for the mushroom mycelium to grow through the compost more quickly.

(B). Spawn Substrates. A number of materials, mostly agricultural wastes, can be used to prepare mushroom spawn. The type of waste available varies from region to region. Some of these wastes are chopped rice straw, sawdust, water hyacinth leaves, used tea leaves, cotton wastes and lotus seed husks. In most laboratories, cereal grains (wheat, rye or sorghum) are used as mother spawn, and agricultural wastes as the planting spawn substrates.  The mother spawn is used to inoculate the final spawn container in which the planting spawn will be produced.  The planting spawn is used to inoculate the mushroom cultivation compost/substrate for fruiting/mushroom production.

(C). Preparation of mother spawn. Here using wheat grains as an example, they are soaked in water for 2 hours or over night. Dead seeds or those that float on water should be carefully removed. Then the grains are washed again and boiled in water for at least 10 to 15 minutes until they expand but not quite broken. The grains are drained and allowed to cool. Precipitated chalk (1.5% on wet basis) is added to the grains. The grains are then loosely packed in bottles which are 2/3 full. These are plugged with cotton wool or covered by double-layered aluminium foil. The grains are sterilised in a pressure cooker for about 1 hour at 121°C, alternatively, they are steamed for 3 to 4 hours in a large cast-iron casserole. The bottles are then cooled prior to inoculation. 

(D). Preparation of planting spawn. Here we shall use rice straw or water hyacinth leaves as an example for Pleurotus sajor-caju planting spawn. The rice straw (or water hyacinth leaves) is chopped into pieces about 2 to 3 cm (1 inch) long, then soaked in water for 4 - 12 hours. The excess water is drained off and the straw pieces mixed with a solution of 1% sucrose, 1.5% chalk and 2% wheat/rice bran in water. The final moisture content is to be adjusted to about 60%. The mixture is then put into glass bottles or plastic bags and sterilised for at least one hour at 121°C before being inoculated with the mother spawn. (E). Remarks for spawn making. Autoclaved substrate can only be justified for spawn production if it is properly done. Otherwise there will be wastage of energy and money through contamination losses.

(F) What means properly? Substrates such as saw dust, straw, cotton seed hulls and so on should not be wet (if water stands on the bottom, mycelia will not enter). Water that is held by capillary forces, and swollen water, will not as readily produce vapour pressure, as does standing water. If the container of spa wn is tightly sealed, air cannot escape, and steam cannot enter properly. Autoclaving is thus imper fect. After proper sterilisation all moulds inside are killed. 


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