This research aimed to study diversity among a collection of Rhizoctonia solani strains, isolated from many crops in Morocco, based on radial mycelial growth on potato dextrose agar (PDA) at different pH and temperature levels. The in vitro antifungal efficacy of essential oils (EOs) derived from aromatic and medicinal plants of Thymus vulgaris, Origanum compactum, Rosmarinus officinalis, Eucalyptus sp., Salvia sp., Cistus ladanifer and Lavandula stoechas was also evaluated by measuring the mycelial growth of this plant pathogenic fungus after placing active mycelial plugs of each strain on Petri dishes using a disc diffusion method of EOs. The Minimum Inhibitory Concentration (MIC) of each EO was also determined. The growth rates observed under different temperatures and pH levels varied among isolates and did not show similar responses for the same levels of the two growth parameters. However, the maximum mycelial growth of the majority of isolates was reached between 20 and 30°C as well as at pH 7. Among the EOs tested, the results revealed that EO of Thymus vulgaris and Origanum compactum were very effective on controlling R. solani strain RS1 with growth inhibition rate of 75,9% and 60,6%, respectively. The MIC of these EOs was at 0.03%. According to the gas chromatography analysis, Carvacrol (61.8%) and thymol (47.8%) are the major constituents of O. compactum and T. vulgaris EOs, respectively, suggesting that these natural compounds have important potential to control R. solani and could be useful for developing effective organic fungicides.

In the greenhouse, mixed inoculation of Tetraclinis articulata (Vahl) Mast.) with Rhizoctonia solani Kühn and Fusarium solani (Mart.) Sacc. caused remarkable damping-off and root rot compared to simple inoculation with one of the two pathogens. Root and stem infections caused significant reduction in plant growth. Root system total length was reduced by 36 to 43% and shoot height losses by 28 to 39%. Plants inoculated by one pathogen were shorter than control plants or inoculated plants by both pathogens. Disease severity ratings for plants infested with the pathogens mixture also were greater than with either pathogen alone up to 62 days post-inoculation. R. solani and F. solani interact synergistically, causing severe damping-off and root rot in T. articulata seedlings.