Volume 10 Part 1 Article 30: Further Investigations on the Bacterial Ecology of the Casing Layer

Volume 10 Part 1 Article 30
Year 1979
Title: Further Investigations on the Bacterial Ecology of the Casing Layer
Authors: P.A. Cresswell and W.A. Hayes


Subsequent to the time of spawning a pasteurized compost, Agaricus bisporus grows in close association with other micro-organisms which may influence its growth in a variety of ways. Especially important are the aerobic bacteria which colonize the compost and the casing layer. The link between nutrition and productivity of composts and thermophilic bacteria which are active in composting was established in previous studies (Hayes 1968,1972; Stanek, 1972). The involvement of bacteria located in the casing layer with the process of fruitbody formation has been established in the studies of Urayama (1961), Eger (1961), Hayes et al. (1969), Hayes (1972), Hume and Hayes (1972). Both associations, in compost and the casing layer may be regarded as advantageous to growth and also to artificial techniques of mushroom culture. In contrast, some bacteria are responsible for some conditions which may be regarded as harmful, at least as far as the commercial process is concerned. These include the well known diseases. Bacterial Blotch (Nair and Fahy, 1973), Drippy Gill (Young, 1970) and Mummy (Schisler et al., 1968).

The casing layer, although often regarded as an inert substrate, has been shown to support an active, aerobic bacterial flora and populations have been shown to fluctuate in a regular manner, which may be associated directly with growth (Hayes, 1974; Hayes and Nair, 1976). Particular emphasis was given to the occurrence of Pseudomonas species which dominate approximately ten days after the application of casing soil, a time which coincided with the important transition from vegetative to reproductive growth. The structure of the casing layer was shown to influence the natural ecology of peat soils.

However, it is not possible to define in precise terms the nature of the association between the bacteria and A. bisporus, but sufficient knowledge is available to suggest ways by which the bacterial flora may be exploited to the improvement of artificial culture techniques.

This paper reports further on the initial stages of colonization of peat casing soils with aerobic bacteria and their extent and gross composition through a cropping cycle both in a peat casing and a new casing medium based on a paper and pulp mill by-product. Initial attempts at manipulating the gross composition of the bacterial flora are described, and further information is given on the influence of single isolates on the initiation and formation of fruitbodies.

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