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Abstract: Commercial mushroom growing is represented by one species in two varieties : Agaricus bisporus var. albus and A. bisporus var. avellaneus; white and brown forms respectively with many commercial strains as intermediaries between them. The early steps in the process of mushroom growing are called 'Commercial Spawn Making' and are carried on in well equipped laboratories under aseptic conditions. The mushroom spores are collected aseptically and planted on a nutritive-gelatinized substrate for germination, by means of multi-spore or single spore isolation methods. Well-grown mycelium is transferred later to the bottles containing sterilized grain. The containers with inoculated grain are kept at a temperature of 75°F until the threads of mycelium have covered the grain. The well-grown mushroom spawn is usually transferred into shipping containers aseptically and placed under refrigeration until time for use. The first commercial spawn was produced on sterilized horse-manure compost (Constantine and Lefort, 1894), but in the industrial evolution, grain spawn (Sinden, 1932, 1937) has been chosen for the biochemical properties as well as practical performance, rather than other substrates. The most used commercial types of spawn today are: rye, wheat and millet grain. Throughout the process of commercial spawn making constant vigilance and careful maintenance must be practised to avoid contamination and assure the purity of spawn cultures. Even, under the optimal conditions contamination by micro-organisms may occur. According to the unofficial estimates, spawn manufacturers lose at least 8-10% by spoilage, caused by contamination, throughout a year. The spoiled spawn normally does not reach mushroom growers but the losses are usually discussed obscurely in the circle of a spawn company. There has been a tendency through the years in the spawn industry to emphasize the type of substrate the spawn is growing on or the type of container the spawn is packed in, but the problem common to all spawn manufacturers : 'The contamination and spoilage of mushroom spawn under the conditions of commercial spawn making', was neglected due to the traditional secrecy and competition from one side and the lack of scientific attention, from the other. Published data on biological description, identification, prevention and control of micro-organisms causing spoilage of mushroom spawn do not exist, so there are no comprehensive references for the spawn laboratories' workers, nor for commercial mushroom growers, who often associate 'crop failure' with a 'bad spawn'. It is virtually impossible for a spawn maker, to predict what type of micro-organisms may gain the entrance through spawn container opening at certain times, but it was possible after years of study to establish the typical pattern of microflora associated with the spoilage of commercial mushroom spawn. Most common species of micro-organisms, isolated from infected commercial spawn belong to the biological groups of: Bacteria, Actinomycetes, Yeast and Fungi. Mostly all species from these groups coincide with the species of micro-organisms ecologically associated with cereal grain.
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