Abstract
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.
Highlights
Rhizoctonia solani Kuhn (Teleomorph: Thanatephorus cucumeris) is one of the most serious soil-borne fungal pathogens, causing disease on a large number of host plant species (Sneh et al, 1991)
Among the essential oils (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
For R. solani, the most favorable temperature regime was from 25 to 35°C (Csöndes et al, 2007), Chang (1985) found that both mycelial growth and sclerotial developpement of R. solani were maximal at pH 7 which confirm the results of our study
Summary
Rhizoctonia solani Kuhn (Teleomorph: Thanatephorus cucumeris) is one of the most serious soil-borne fungal pathogens, causing disease on a large number of host plant species (Sneh et al, 1991). Many crops of economic importance worldwide are frequently affected by R. solani including potato, bean, tomato, soybean, strawberry and tulip, (Kotba et al, 2018; Lahlali and Hijri, 2010; Ismail & Ismail, 2011; Naher et al, 2014) Isolates of this pathogen has a complex biology and diversity in terms of myclial colour, size of aerial mycelium, growth rate, zonation, type and number of sclerotia, saprophytic behaviour, enzyme production and pathogenicity (Hyakumachi et al, 1988; Salunkhe et al 2008). Chemical control is not completely effective, and Rhizoctonia disease still damages diverse crops (Goudjal et al, 2014) To overcome this challenge, the use of plants extracts may be an alternative to conventional fungicides to control R. solani. The objectives of this study were to i) demonstrate the existing diversity among R. solani isolates based on growth at different pH and temperature regimes on culture media, ii) determine the efficacy of some plant-derived EOs against the growth of R. solani in laboratory assays, iii) identify the major constituents of these oils by gas chromatography method using appropriate detectors
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