VIABILITY OF AQUATIC HYPHOMYCETE CONIDIA IN FOAM

The viability of aquatic hyphomycete conidia trapped in foam was estim ated with tetrazolium bromide. In fresh foam, 76-91% of all conidia ha d at least one viable cell; in old foam, these values were 20-43 %. Th e average number of viable cells per conidium was higher in fresh than in old foam. Laboratory-produced conidia of Heliscus lugdunensis and Articulo-spora tetracladia had much higher numbers of viable cells tha n field-collected conidia. Viability as defined in this study (at leas t one viable cell per conidium) proved to be an excellent predictor of ability to germinate. Conidia of four species (two Canadian and two I ndian strains) did not survive for more than 24 d when exposed to -17 degrees C, or to freeze - thaw cycles. Persistence of conidia through unfavourable conditions therefore seems limited.