The antifungal effect of some herbal essences on the causal agent of tomato and crown root rot, Phytophthora parasitica L. in vitro and greenhouse conditions

Phytophthora stem and root rot of tomato, Phytophthora parasitica L., is one of the most important soil-borne diseases of tomato. This disease has been spreading in greenhouses located in east-south of Tehran province (Varamin) through the last decade. The disease control by fungicides has not been successful; In spite of success of biological control or using resistant varieties to reduce disease, it seems that studying and application of natural compounds especially plant essences including a wide range of secondary metabolites can not only reduce disease but also it has beneficial effects on the environment. In this case study, efficacy of eight plants including thyme, cumin, savory, pennyroyal, mint, tarragon, ajwain and fennel with Ridomil-mancozeb fungicide as control were evaluated on colony growth rate and inhibitory growth of causal agent in five concentrations of 60,120,180, 240 and 300 ppm on PDA medium based on completely randomized block design in vitro conditions. Greenhouse experiments were carried out with ten treatments including successful essences of thyme, pennyroyal and fennel at 0.2 and 0.3 with Ridomil-mancozeb fungicide at 1 and 1.5 ppm and check and control infected with P. parasitica in completely randomized block design in four replications. Essences and fungicide were added into root substrate of tomato seedlings in two leaves stage. Recording disease severity percentage was performed according to Quesada-Ocampo and Hausbeck scale, four weeks after inoculation. Essences with highest inhibitory growth percentage in laboratory were respectively thyme (79.28%), pennyroyal (72.85%), cumin (69.95%), mint (60.70%), tarragon (60.70%) and ajwain (60%) and thyme and pennyroyal essence by concentration of 180 ppm showed minimum inhibitory concentration, EC50 of mycelial growth. Results of variance analysis in greenhouse demonstrated that all treatments were significantly different at 1% confidence level. Mean comparisons by Duncan multiple range test showed that thyme essence respectively with disease severity index of 1.65 and 1.31 were classified statistically in e, d that were the closest index with fungicide treatments of Ridomil-mancozeb and cheek (18% DSI) and it has been proved the best efficacy on disease reduction.