Six biological control agents, four commercial products with Trichoderma harzianum, one with Streptomyces sp., and one with Bacillus subtilis were tested for their ability to reduce root infection with Spongospora subterranea f. sp. subterranea, the causal agent of powdery scab and the vector of the spraing-provoking Potato mop-top virus. Inoculum of resting spore balls of S. subterranea was mixed with each control agent in glasshouse pot experiments using tomato as host plant. The two T. harzianum-contarning products: TRI 002 and Binab TF significantly reduced the root infection level by zoosporangia of S. subterranea. However, this was not unambiguously reflected in an increased growth of shoot and roots of the host plant. In all experiments, the root inoculation with S. subterranea alone resulted in significant reductions of shoot and root mass. The results indicate a potential use of selected strains of T. harzianum as seed dressing to control spread of S. subterranea and Potato mop-top virus from seed potatoes.
