Volume 10 Part 1 Article 47: Studies on Primordium Initiation in Agaricus bisporus and Agaricus bitorquis (Syn. edulis)

Volume 10 Part 1 Article 47
Year 1979
Title: Studies on Primordium Initiation in Agaricus bisporus and Agaricus bitorquis (Syn. edulis)
Author: D.A. Wood


Most strains of the cultivated mushroom Agaricus bisporus do not form sporophore primordia on conventional fungal culture media. In commercial mushroom production fructification of A. bisporus is achieved by covering mycelium-colonised compost with a layer of soil or peat-chalk mixture known as casing layer. Eger (1961) showed that this layer must contain a viable microbial flora for fruiting to be initiated. Other workers (Hayes, Randle and Last, 1969) isolated several strains of bacteria from casing layers which, when returned to sterile casing layers induced the production of fruit bodies. Hume and Hayes (1972) presented evidence that these bacteria which were identified as strains of Pseudomonas putida could stimulate some A. bisporus strains to produce sporophore primordia in axenically grown fungal cultures on malt extract medium. Culture filtrates of these bacteria grown on an ethanol-basal salts medium were also said to produce a similar effect. Park and Agnihotri (1969) using sterilised soil or soil extract agar to support axenic growth of A. bisporus showed that a range of soil bacteria or their culture filtrates would promote fruit body production in axenic cultures of A. bisporus. It has also been claimed that primordium formation of A. bisporus is stimulated by adding chelating agents or iron containing compounds to axenically grown plate cultures of the fungus. (Hayes, 1972; Smith and Berry, 1974; Hayes, 1974) suggested that the P. putida might act to bring about fruiting initiation by producing iron-chelating compounds which would bind iron from the sequestering conditions of the alkaline casing layer thereby initiating fruiting. No chemical evidence has yet been presented as to the nature of these chelating compounds from the P. putida flora of the casing layer but it seems likely they would be similar in properties to the naturally occurring microbially produced iron binding compounds such as the sideramines and siderochromes (Neilands, 1974).

Most commercial strains of A. bisporus do not initiate fruit bodies synchronously and replication of initiation between individual petri plate cultures is variable (Wood, 1976). Strains of A. bisporus which initiate at high frequency and with synchrony would be useful for cytological and biochemical studies of fruit body initiation and would also be useful for bioassaying the effect of possible inhibitors or stimulators of fruiting.

Commercial interest in the production of an alternative species of Agaricus, namely A. bitorquis is increasing owing to its greater resistance to higher temperature and carbon dioxide levels during fruiting initiation and to the claim that it is resistant to the virus infections found in strains of A. bisporus.

This paper describes studies on the capacity of commercial strains of A. bisporus to form primordia on malt agar in axenic conditions and examines the effect of concentration, composition and quantity of medium on primordium formation. It also examines the effect of compounds suggested to promote primordium formation in A. bisporus and other basidiomycetes and also whether such effects are produced by strains of P. putida or culture filtrates of that organism. In addition, the formation of fruiting initials (aggregates) of the A. bisporus strains B430 and B431 is compared with those of several commercial strains of A. bisporus and with that in a wild type and some derived heterokaryons of A. bitorquis.

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