CADMIUM AND MANGANESE IN CONTRAST TO CALCIUM REDUCE YIELD AND NUTRITIONAL VALUES OF THE EDIBLE MUSHROOM PLEUROTUS-PULMONARIUS

Pleurotus pulmonarius is a species of the oyster mushroom which has be come the second most popularly cultivated mushroom in the world. In th is study, we show that renewed fruiting from excised stipes can be use d as a simple and rapid in vitro bioassay system to detect fruiting mo dulators. We used this and conventional cultivation techniques to exam ine the effects of cadmium, a potential contaminant from industrial so urces, calcium, which is an ingredient in mushroom compost, and mangan ese, which has been claimed to improve the yield of P. ostreatus. All the three metallic salts did not affect sporulation. Calcium chloride addition shortened the time taken for the mushroom to fully cover the cultivation compost and improved yield. Insoluble calcium salts at hig her concentrations had a similar though less pronounced effect. The ca lcium and total amino acid contents of fruit bodies also increased. Co mpost supplementation with calcium is desirable for cultivation of the oyster mushroom but not indispensable since the straw-based cultivati on substrate is itself able to provide the required minerals. By contr ast, manganese chloride retarded mycelial growth and decreased yield b ut increased the total amino acid content in the stipe whilst manganes e sulphate did not enhance accumulation of manganese into fruit bodies . Excess manganese induced browning of vegetative tissues. Cadmium ion s did not kill the oyster mushroom at 4.5 mM but reduced yield by 50%. At this concentration cadmium decreased the total amino acid content and affected the amino acid profile but did not affect the form and sh ape of the fruit bodies. Pleurotus pulmonarius concentrated cadmium to such an extent that consumption of as little as 20 g (D.W.) of the mo st contaminated samples would exceed the weekly limit tolerated by hum ans and thus pose a health hazard. Monitoring the heavy metal contents of mushrooms marketed for food is, therefore, advised as the source o f the substrate for cultivation is usually not known.