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Abstract: One of the main limitations in critical studies of the physiology of sporophore initiation and development in Agaricus bisporus is the lack of simple easily conducted laboratory techniques in petri-plates for the obtention of primordia and fruiting bodies, without utilizing compost, grain spawn or soil. Both compost and soil (or other casing material) are unpredictable in nature and they thus impose a serious constraint not only in normal production systems but also in experimentation concerning nutrition requirements and sporophore initiation. So far the most elusive aspect in the life cycle of Agaricus bisporus is the fruiting process. A. bisporus forms abundant fruiting bodies when the colonized composts is cased with a layer of unsterile soil or peat but not when maintained in rigidly sterile conditions. It has been argued that the inability of A. bisporus to fruit unless a casing layer is applied may well be the greatest asset of this fungus (Peerally, 1979), since profuse fruiting may be induced at will under commercial conditions,, thus avoiding unpredictable sporophore formation. Attempts to develop techniques on fruiting in A. bisporus in small scale laboratory studies have been described by various authors. These reports involved cased grain spawn. (San Antonio, 1971), autoclaved substrates (Smith and Hayes, 1972), petriplate methods using soil (Eger, 1962; Peerally, 1979) or apetriplate agar technique (Hume and Hayes, 1972). The petri-plate techniques described differ fundamentally from the commercial system in their horizontal method of growth. All these techniques have their own specific usefulness. A review of the literature reveals that studies on the physiology of sporophore initiation in A. bisporus have got bogged down, mainly on account of the lack of techniques which are simple and easily reproducible. It has been concluded by Peerally (1979) that the change which occurs in the life cycle of A. bisporus before the mycelium develops fruiting bodies involves a modification of the profusely branched vegetative mycelium into sparsely branched stranded reproductive mycelium maintly as a result of the action of bacteria present in the casing. Wood (1976), working in axenic agar cultures.observed that primordium formation was usually associated with strands but no primordia were obtained before complete colonization of the plate which took 3 to 4 weeks. In an attempt to alleviate the bottlenecks which exist in these studies, efforts were made to develop a technique which permitted fruiting in purely agar cultures in the presence of a selected bacterial flora isolated from casing soil. The technique described in this paper achieved 40 to 60 percent success (presence of a single primordium per plate was considered successful) in two experiments'which were carried out. It must be pointed out that lack of sophisticated laboratory equipment imposed some constraints in our work. Additional work is required to refine upon it.
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