MYCOPARASITISM OF PYTHIUM-ULTIMUM BY ANTAGONISTIC BINUCLEATE RHIZOCTONIA ISOLATES IN AGAR MEDIA AND ON CAPSICUM SEEDS

Hyphal interactions between two antagonistic binucleate Rhizoctonia is olates (BNR) and the seedling damping-off pathogen, Pythium ultimum va r. sporangiiferum, were observed by both light-and scanning electron m icroscopy (SEM), on agar media and on capsicum seeds in sterilized pot ting mix. Both BNR isolates displayed similar mycoparasitic behaviour towards P. u. sporangiiferum on agar media. This included parallel gro wth along the pathogen hyphae, formation of hook-shaped hyphal tips an d coils on the surface of P. u. sporangiiferum hyphae and penetration and growth within pathogen structures. Disruption of cytoplasmic strea ming and disorganisation of pathogen cytoplasm were also observed. SEM observations revealed alterations in P. u. sporangiiferum cell wall s tructure and the presence of penetration holes apparently due to diges tion by the BNR. P. u. sporangiiferum was also parasitised by both BNR isolates on capsicum seed coats, with parallel growth, hook formation and coils commonly observed. The above observations indicated that my coparasitism is a possible mode of action of BNR against P. u. sporang iiferum.