Fig. 3

Mycoparasitic mycelium infested Agaricus xanthodermus mushrooms at different developmental stages in a larger disease outbreak in the 3rd week of September of 2015. a, b Foreign mycelium grew from surrounding moss to a primordium and the stipe base of a young mushroom at the stage of stipe elongation and cap growth. c 24 h later the stipe base was surrounded by a thick layer of foreign mycelium, the stipe and cap were enlarged but the cap laid down on the floor due to strong bending of the stipe. d–m Strong white mycelium found at multiple places in the grass and moss served as infection source of A. xanthodermus. Bases of elongating stipes of growing drum-stick-like young mushrooms were covered by a layer of foreign mycelium (d, f) and the same structures 24 h later photographed from different angles (e, g). While the yet less infected structure with the foreign mycelium confined only to the stipe base was still erect (e), the heavily infected structure with foreign mycelium reaching up to the cap already collapsed (g). Infested young mushrooms at the start of partial veil rupture (h, i). 24 h later, the cap of the mushroom shown in i coloured brownish and the rupture of the partial veil blocked. Thick white patches of the pathogen were obvious on the cap surface (see arrow; j). Also young stages of opened caps (the arrows mark the skirt-like annulus injured by the infestation) were attacked by mycelium growing upwards the stipe (k) and eventually also onto the lamellae (l, m). Rapid decolourization and mushroom collapse within 24 h resulted from strong pathogen infestation (l, m). Strong white mycelium found at multiple places in the grass and moss (n)