Morphogenesis and significance of hyphal coiling by nematode-trapping fungi in mycoparasitic relationships

Abstract

The mycoparasitic behaviour of some nematode-trapping fungi was investigated. These organisms interacted with other soil fungi by hyphal coiling around the host hyphae. A detailed study with Arthrobotrys oligospora revealed that different fungi, representing all taxonomic groups, were attacked. In dual cultures, the interaction between A. oligospora and Rhizoctonia solani occurred soon after hyphal contact, irrespective of the nutrient level of the medium. Coiling was also observed when the two organisms were grown in sterilized soil. The coils possessed a high metabolic activity compared to the surrounding hyphae, as was indicated by fluorescence microscopy of fluorescein diacetate (FDA)-stained preparations. On the ultrastructural level, developing coils showed an abundance of membranous vesicles which developed from tubular-shaped endoplasmic reticulum. At the site of coiling, a strong cell wall proliferation was observed in the Rhizoctonia cells. The cytoplasm of these cells subsequently disintegrated. The death of the cells was confirmed in vital staining experiments. Penetration of intact Rhizoctonia cells was not observed. The interaction between A. oligospora and R. solani is interpreted in terms of competition for nutrients.