THE
'FUZ' REACTION
Mating interactions can be tested in a so-called 'Fuz' reaction by mixing cultures of unknown sex with tester
strains of known mating type (i.e., MAT-1 or MAT-2) on medium
containing black, activated charcoal. Cells of opposite mating type will sense
each others pheromones and respond by putting out conjugation tubes which will
fuse to produce straight-growing, dikaryotic hyphe. In this plate assay this is seen as a white, fuzzy
reaction. In contrast, mixing cells of the same mating type will not respond
and consequently the colonies will remain smooth. Charcoal makes the Fuz reaction more pronounced, presumably by adsorbing an
inhibitor.
In this example different random progeny from a sample of U. scitaminea teliospores (horizontal rows) were tested
against tester strains (2nd and 3rd vertical rows). U. scitamineais the sugarcane smut which has a
bipolar mating system (courtesy of Dr. Kathy Braithwaite).