Fungal Organisms Isolated from Rotted White Yam (Dioscorea rotundata) Tubers and Antagonistic Potential of Trichoderma harzianum against Colletotrichum Species

Nine fungal organisms were isolated from rotted white yam (Dioscorea rotundata) tubers from Kadarko, Nasarawa, Nigeria between February and May, 2015. Trichoderma harzianum was used as a biological agent to evaluate its potential against Colletotrichum species isolated from rotted white yam tubers in dual culture method at Advanced Plant Pathology Laboratory, Federal University of Agriculture, Makurdi, Nigeria. Percentage frequency of occurrence of the isolated fungal organisms was determined at monthly interval. The test antagonist (T. harzianum) was introduced at three different times (same time with Colletotrichum spp, two days before the inoculation of Colletotrichum spp and two days after the inoculation of Colletotrichum spp). The plates were incubated for 192 hours and measurements of mycelial radial growths were recorded at intervals of 24 hours beginning from the third day. The results of the in vitro interactions between T. harzianum and Colletotrichum spp revealed that T. harzianum was able to significantly (P≤0.05) inhibit the growth of Colletotrichum spp. Mean percentage growth inhibition was found to be highest (50.61%) when T. harzianum was introduced 2 days before inoculation of Colletotrichum spp followed by introduction of T. harzianum same with Colletotrichum spp (37.12%) with the least percentage growth inhibition (12.48%) recorded when the antagonist was introduced 2 days after inoculation of the pathogen. Minimum inhibition concentration (MIC) showed slightly effective to effective control indicating that the antagonist has the potential for biological control of Colletotrichum spp at all levels. It is therefore, recommended that the biological agent should be introduced prior to infection in order to be more effective in controlling the pathogenic fungus.

Keywords: Inoculation; Incubation; Inhibition; Effective; Biological agent