Kinetics and optimization of insecticidal and fungicidal effects of Thymus vulgaris and T. kotschyanus essential oils using response surface methodology

Ebadollahi, asgar and Taghinezhad, Ebrahim and Davari, Mahdi Kinetics and optimization of insecticidal and fungicidal effects of Thymus vulgaris and T. kotschyanus essential oils using response surface methodology. University of Mohaghegh Ardabili.

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Abstract

Application of synthetic chemicals for management of damaging agents of agricultural products caused several side-effects such as a threat to humans and environmental contamination. Plant origin materials with low mammalian toxicity and biodegradable characteristic may be considered as capable alternatives to the chemicals. In the present study, the fumigant toxicity and growth inhibitory effects of the essential oils of Thymus vulgaris and T. kotschyanus were evaluated, respectively, against the lesser grain borer (Rhyzopertha dominica) and the pathogenic fungi Fusarium graminearum and Botrytis cinerea¬. Further, the chemical composition of the essential oils was assessed through Gas Chromatography-Mass Spectrometry and it was found that the terpenic compounds such as geranyl acetate, α-terpinole and linalool had a high percentage of both essential oils. T. vulgaris and T. kotschyanus essential oils had a significant toxicity on the adults of R. dominica. Estimated models for fumigant toxicity of essential oils are grade-three regression models, in which A and B were the exposure time of insect pests and the of essential oils’ concentrations. The concentration of 43.10 μl/l and 60-h exposure time was evaluated as the optimum condition for 72.23% mortality with the desirability of 87% by the essential oil of T. vulgaris. Also, the concentration of 51.72 μl/l and 60-h exposure time was estimated as the optimum condition for 72.15% mortality with the desirability of 88% by T. kotschyanus essential oil. T. vulgaris and T. kotschyanus essential oils significantly reduced the mycelial growth of F. graminearum and B. cinerea fungi. Optimization of the antifungal effects showed the time of 59.88 hours and 486.66 ppm concentration of T. vulgaris essential oil would inhibit the mycelial growth of in F. graminearum to 88.67%. Also, 74.01-h and the concentration of 552.96 ppm from T. vulgaris essential oil would need for 94.43% growth inhibitory of B. cinerea. The required time and concentration for 88.31% of mycelial growth inhibition of F. graminearum was 96 h and 600 ppm, respectively, with T. kotschyanus essential oil. Also, for 92.52% mycelial growth inhibition in B. cinerea, 74.98-h time and the concentration of 746.20 ppm of this essential oil will be enough. The results exhibited that the essential oils of T. vulgaris and T. kotschyanus have a high potential for management of lesser grain borer and F. graminearum and B. cinerea fungi.

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