Determination, by fluorescein diacetate staining, of fungal viability during mycoparasitism

Trichoderma hamatum is a mycoparasite of Rhizoctonia solani. When stained with the vital stain fluorescein diacetate (FDA), both interacting fungi showed fluorescence during the first 24 h of incubation. Thereafter R. solani showed only a faint fluorescence while T. hamatum was still glowing up to 7 days. When each of these fungi were grown alone they showed a significant fluorescence for 4 days. This technique for determination of fungal viability during mycoparasitism may indicate that the initial attack occurs while the host is still alive.