Discoloration and tyrosinase activity in Agaricus bisporus fruit bodies infected with various pathogens

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 (Delta L = 54.7, Delta a = 16.6, Delta b = 28.7%). Th e colour change provoked by P. gingeri had a characteristic profile differe nt from P. tolaasii (Delta L = 36.3, Delta a = 14.1, Delta b = 49.5%). P. a garici and P. reactans provoked only a slight increase of red colour. Respo nse to T. harzianum was orange, and to V. fungicola brown, similar to P. to laasii but paler and more yellowish. All pathogens except P. reactans provo ked degradation of total tyrosinase to variable extents. Activation of tyro sinase was only observed after infection with P. tolaasii (to almost 7%) an d V. fungicola (to 3%).