Antagonistic Activity of Five Myrothecium Species Against Fungi and Bacteria in Vitro

Antagonistic activity of 69 Myrothecium isolates belonging to M. carmichaelu, M. cinctum, M. roridum, M. tongaense and M. verrucaria against six soil-borne plant pathogenic fungi was investigated by using the streak method. Results clearly showed that M. carmichaelu is a strong antibiont having a very high degree of antifungal efficacy. M. cinctum and M. tongaense isolates were found to have an antagonistic activity either through antibiosis or mycoparasitism or both against the test fungi. M. roridum and M. verrucaria isolates also possessed both kinds of activities. After this first screening (of all Myrothecium isolates), one isolate from each species exhibiting the highest degree of antagonistic activity was selected for further studies. Inhibitory effects of culture filtrates of these representative isolates on the mycelial growth of the test fungi were investigated by incorporating them into PDA at a dilution of 1:8. M. carmichaelu was the most and M. cinctum the least effective species under assay. Moreover, culture filtrates and mycelium extracts of the selected isolates were found to have both antifungal and antibacterial properties using the agar-well method. Among the test fungi, Sclerotinia sclerotiorum proved to be generally the most, and Pythium debaryanum the least sensitive to the antibiotic effects. M. cinctum showed the widest antibacterial spectrum inhibiting five bacterial species except for Pseudomonas syringae Pv. Phaseolicola. Additionally, the observations using light and scanning electron microscopy clearly demonstrated that all of the five Myrothecium species were able to parasitize all of the tested fungi.