The discoloration of A. bisporus after infection by Pseudomonas tolaasii, P. gingeri, P. agarici, P. reactans, Verticillium fungicola and
Trichoderma harzianum can be distinguished by chromametric measurements. Infection with P. tolaasii caused a specific colour change,
independent of the bacterial concentration applied (ΔL = 54.7, Δa = 16.6, Δb = 28.7%). The colour change provoked by P. gingeri
had a characteristic profile different from P. tolaasii (ΔL = 36.3, Δa = 14.1, Δb = 49.5%). P. agarici and P. reactans provoked only a
slight increase of red colour. Response to T. harzianum was orange, and to V. fungicola brown, similar to P. tolaasii but paler and
more yellowish. All pathogens except P. reactans provoked degradation of total tyrosinase to variable extents. Activation of
tyrosinase was only observed after infection with P. tolaasii (to almost 7%) and V. fungicola (to 3%).