**Abstract**

*Rhizoctonia solani* is one of the most important causative agents of damping-off diseases on cucumber plants and significantly reduces their yield. *R. solani* possesses some characteristics, such as wide host range and unlimited survival in soil, which made it most difficult to control. Therefore, the research for a biocontrol agent will be valuable to control this disease. Two species of mycorrhizal fungi (*Glomus mosseae* and *Glomus clarum*) that were evaluated against the agent *R. solani* reduced the damping-off disease on the cucumber plant. Mycorrhizal-inoculated plants with both species showed a significant reduction in disease severity (*DS*), which were 21 and 25%, respectively, whereas the disease severity was 65% for non-inoculated plants. Furthermore, the effects of mycorrhizal fungi were evaluated against the growth parameters of cucumber plants. Plants inoculated with both species of mycorrhizal fungi showed a significant increase in both shoot dry weight and root dry weight compared with uninoculated plants. In conclusion, both mycorrhiza species could be an important tool to control soil-borne pathogens, increase plant's nutrients' absorption, and increase resistance to abiotic stresses.

**Keywords:** biological control, *Rhizoctonia solani*, arbuscular mycorrhiza, cucumber, damping-off diseases
