Tobacco production has intentions to promote biological control as a modern and environmentally friendly plant protection measure.

Rhizoctonia solani is a very destructive pathogen, the causing agent of damping-off in tobacco seedlings.

Biocontrol activity of some Trichoderma species (T. aureoviride, T. hamatum and T. harzianum) was investigated in vitro - by dual culturing technique and in vivo - in the greenhouse.

The relative development of the pathogen ranged from 33.10% for T. harzianum to 41.64% for T. aureoviride. The percentage inhibition of radial growth of the pathogen did not show differences among the studied Trichoderma species, however, the highest value (66.91%) was in T. harzianum.

In conditions of artificial inoculation, the intensity of a disease was reduced when applying the investigated biocontrol agents.

T. harzianum has the best reducing effect on damping-off in all application methods of this biocontrol agent. The intensity of disease was only 5.56% in the application 15 days after sowing, while in the application before sowing and mixed with seeds, there was no disease incidence.

Application of these Trichoderma species on seeds was confirmed as the best application method of the biocotrol agent.

The biocontrol activity of these fungi enables them to be used in the biological control of R. solani in tobacco seedling protection.