I Chet, P Boyle, Y Henis

Hyphal interactions between either Trichoderma harzianum or T. hamatum, and Sclerotium rolfsii or Rhizoctonia solani were observed by scanning electron microscopy. Trichoderma spp. attached to the host either by hyphal coils, hooks, or appressoria. Lysed sites and penetration holes were found in hyphae of the plant pathogenic fungi, following removal of parasitic hyphae. High β-(1,3) glucanase and chitinase activities were detected in dual agar cultures when T. harzianum parasitized S. rolfsii, compared with low levels found with either fungus alone. In the presence of cycloheximide, antagonism was prevented and enzymatic activity was diminished. Interaction sites were stained by fluorescein isothiocyanate-conjugated lectins or Calcofluor White M2R New. Appearance of fluorescence indicated the presence of localized cell wall lysis at points of interaction between the antagonist and its host.