Abstract
Abstract: Rhizoctonia solani isolates were obtained from infected potato tubers (cv. Spunta). Four isolates of Trichoderma spp., namely Trichoderma harzianum,T. viride, T. longibrachiatum, and T. album, were applied to test their antagonistic effects on growth and development of the obtained isolates of R. solani. Interactions between the antagonistic fungal isolates and R. solani were studied in dual culture, antagonism and volatile,nonvolatile techniques. All the tested Trichoderma isolates showed significant antagonistic effects on the tested R. solani isolates. They produced inhibition zones in front of the R. solani colonies, but in varying degrees. T. harzianum isolates were able to overgrow the mycelium of R. solani, compared to those of the other Trichoderma isolates.All the antagonists suppressed the formation of sclerotia. This resulted in the reduction of the mycelial growth of the R. solani isolates. The results implied that the extent of inhibition by T. harzianum provides the use of excellent potential antagonists capable of controlling the pathogenicity of R. solani on Potato.