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).