Using a method known as the ‘halbschalentest ’, Eger
(1961) showed that the casing layer must contain a viable
microbiota for normal fruiting to occur. The interaction
between A. bisporus and the micro-organisms present in the
casing layer was studied by electron microscopy. Masaphy et
al. (1987) found that rodlike bacteria from the casing soil
attached firmly to hyphae at the time of fruit body initiation
and similarly, attachment of the casing layer micro-organisms
Pseudomonas putida and P. tolaasii to sterile hyphae was
observed by Miller, Gillespie & Doyle (1995). Upon addition
to sterilized casing, isolates of P. putida induced formation of
fruit body initials (Hayes, Randle & Last, 1969 ; Reddy &
Patrick, 1990) and the same effect was observed on malt agar
(Hume & Hayes, 1972). With commercial strains, aseptic
fruiting on malt agar was also attempted and, at a low
frequency, formation of hyphal aggregates or cords and
primordia was observed. However, these fruit bodies were
arrested at the primordial stage of development (Wood,
1976).