Trichoderma hamatum: Its hyphal interactions withRhizoctonia solani andPythium spp.

The mode of hyphal interaction and parasitism ofPythium spp. andRhizoctonia solani byTrichoderma hamatum was studied by both phase-contrast and Nomarski differential interference-contrast microscopy. Directed growth of the mycoparasite toward its host was observed. In the area of interaction,T. hamatum produced appressorial-like structures attached to the host cell wall. Subsequently, several different types of interactions occurred.T. hamatum either grew parallel to and along the host hypha or coiled around its host. In the contrast regions the parasite formed bulbular or hook-like structures that contained granular cytoplasm. In other cases the parasite penetrated into and grew within the mycelium ofR. solani orP. ultimum. As a consequence of the attack, the host hypha became vacuolated, shrank, collapsed, and finally disintegrated. These observations suggest the involvement of parasitism followed by lysis rather than involvement of antibiotics in this host-mycoparasite relationship.