Study on the effect of some plant essential oils on two fungal causal agents of bean root rot, Fusarium solani and Rhizoctonia solani in Zanjan Province

Inhibitory effect of essential oils from four medicinal plants, shirazi thyme (Zataria multiflora Boiss.), pepper mint (Mentha piperita L.), eucalyptus (Eucalyptus camadulensis Dehnh.) and fennel (Foeniculum vulgare Miller.) was investigated against two major causal agents of bean root rot in Zanjan province, Fusarium solani and Rhizoctonia solani. For this purpose, anti-fungal index (AI) of essential oils against disease causing fungi was investigated by reverse petri dish method in four concentrations of 100, 200, 300 and 400 ppm in five replicates for each treatment. Based on laboratory results, all concentrations of shirazi thyme and peppermint essential oils had the most inhibitory effect (AI = 100%) on R. solani, also all concentrations of shirazi thyme as well as one concentration of peppermint (400ppm) had complete inhibitory effect on F. solani (P=0.05). To investigate the synergistic effect between essential oil of peppermint and thyme, six mixing ratios of them were assessed. The results indicated synergistic effect between two essential oils against F. solani. To study the effect of essential oils and their mixtures on disease control under greenhouse conditions, the soil of pots was inoculated with both pathogens simultaneously, then the seeds of red bean cultivar Naz were sown after treatment with different concentrations of essential oils with four replications for each treatment (concentrations: 200, 400, 600, 800, 1000, 1500, 2000, 2500, 3000, 3500 ppm). Seed treatment with essential oils decreased the disease significantly. The most effective combination ratios of thyme and peppermint for disease control were 80:20 and 60:40. The most effective treatment for disease control was 1500 ppm of the combination of thyme and peppermint in the ratio of 60:40 (P=0.05).