Growth kinetics of Agaricus bisporus mycelium on solid substrate (mushroom compost)

Growth of Agaricus bisporus was studied on sterile compost and on sterile compost pre-grown with the thermophilic fungus Scytalidium thermophilum. Early growth was characterized by depressed, slowly growing hyphae. The mycelial radius extended exponentially in this stage. Mycelium on sterile compost switched to a fluffy growth type of radially orientated hyphae that extended at a linear rate, K r, of 5 mm d−1. On compost pre-grown with S. thermophilum, early growth continued up to 30 mm, then extension became linear at K r = 7·2 mm d−1. If cultures were well ventilated, K r was higher. A new growth function was derived to combine both growth phases. The width of the peripheral growth zone, w, of A. bisporus mycelium was 3 mm. The exponential specific growth rate, μ, was calculated from K r/w = 2·4 d−1, which is much higher than a previous estimate of 0·19 d−1. In addition to growth-promoting effects, S. thermophilum had inhibitory effects; the period of early growth was reduced if S. thermophilum was inactivated in pre-grown compost. Under commercial conditions, maximum growth rates are not exploited. The introduction of selected strains of thermophilic fungi in compost and the development of a new kind of spawn inoculum of A. bisporus might lead to improvements in commercial practice.