Volume 17 Part 1 Article 28: Microbial Dynamics of Different Casing Materials in the Production of Button Mushrooms (Agaricus bisporus)

Volume 17 Part 1 Article 28
Year 2008
Title: Microbial Dynamics of Different Casing Materials in the Production of Button Mushrooms (Agaricus bisporus)
Authors: N. Afewerki Siyoum and L. Korsten


Since peat is a limited resource in South Africa, its mining has now been restricted due to the rapid depletion of this natural resource. Local peat is used as a casing layer in the commercial production of white button mushrooms (Agaricus bisporus (Lange)). Consequently, research is being done at the University of Pretoria to find alternative casing materials, either to replace peat or to extend existing peat supplies or imported peat. How the casing layer initiates the formation of mushroom fruiting bodies is not well understood. It is suggested that micro-organisms present in the casing material may play an important role in this process. In this study, microbial population dynamics were assessed in peat and other casing materials. Trials were carried out in a semi-commercial growing unit. Casing mixtures were prepared by mixing South African peat with the following industrial wastes in different ratios: coir (coconut industry), composted wattle bark (timber industry), and bagasse and filter cake (sugar industry). Unmixed materials were examined for fluctuating microbial populations before and after pasteurisation. In addition, the casing mixtures were examined at three stages of the growing cycle: before casing, at pinning of first break and at the end of second break. The spread plating technique was used to examine microbial diversity and species richness of casing materials and mixtures. Pasteurisation decreased the microbial richness and/or diversity of all materials tested. Total bacterial counts increased from casing to pinning and either increased or remained the same at the end of the second break. Assessment of fungal population dynamics throughout the growth stages is under progress. The increase of bacteria towards pinning could contribute in the transformation process of mycelium. Therefore, alternative casing materials should allow good growth of bacteria. Currently, molecular analysis is being done using degenerating gradient gel electrophoresis (DGGE) to investigate the microbial profile of the casing materials.

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