Extended Abstract

Introduction: Greenhouse cucumber is one of the most importance economic crops in Iran and many countries of the world. Many diseases threaten cucumber, and in other words, this product is always exposed to pathogenic organisms in its living environment, in which fungi and other plant pathogens cause many losses in vegetable and summer fields in Iran and around the world. Destructive diseases that cause significant damage to vegetable and summer crops in fields and greenhouses every year are seedling death disease and plant death disease caused by Phytophthora pseudofungus. The use of plant extracts and essential oils are of great value because so far no resistance to these types of compounds has been observed in pests and diseases, perhaps the reason for this is the presence of various effective compounds in these compounds and considering. The existing problems regarding the use of fungicides, study and research on new and reliable and low-cost methods for the control and management of plant diseases is a necessity for agriculture mangment in the world. In this study, the antifungal effects of denaei thyme essential oil (Zataria multiflora) & two fungicides fusetyl aluminum & metalaxyl-mancozeb were investigated to control the disease of greenhouse cucumber caused by Phytophthora.
Materials and Methods: In autumn and winter of 2018, sampling of cucumber greenhouses suspected of contamination was done in Garmsar city, Semnan province, Iran. The pathogenicity test of pseudofungal isolates was performed. Cucumber seeds were transferred to pots after germination and having two leaves. In the three- to four-leaf stage of the seedlings, the soil near the crown and roots was removed and the colony causing Phythophthora disease was placed next to the crown. In the control treatment, only pure culture medium without pseudofungi was used. Disease evaluation was done one month later. The test of mixing these three factors (thyme essential oil & two fungicides fosetil aluminum & metalaxyl-mancozeb) was used for laboratory tests. In this research, in addition to the effect of denaei thyme essential oil, fustil aluminum and metalaxyl-mancozeb were also used in five concentrations of 5, 15, 30, 45 and 60 ppm on Phytophthora pseudofungus. In order to determine the inhibition percentage of denaeithyme extract. Also,denaei thyme extract was evaluated in different concentrations including 250, 500, 1000, 1500 and 2000 ppm. In  greenhouse tests including pathogenicity test, evaluation of the mentioned treatments on the symptoms of the disease caused by Phytophthora sp. The activity of peroxidase, catalase & phenylalanine ammonialyase was also investigated. In tirst, the seeds of the cucumber plant after disinfection and cultivation in pots, in the stage of three to four leaves, according to the method of proving pathogenicity, respectively, the pathogen of Phytophthora sp. were inoculated (Gholamnezhad et al., 2016). After 24 hours, 50 ml of denaei thyme extract and the fungicides used in this research were added to the soil around the roots of the plants infected with the pathogen with a concentration of 1500 and 150 ppm, respectively.
Results and Discussion: The results showed that among the five fungal isolates studied in this study, isolates P1 & P5 caused more disease (78.52 & 62.68%, respectively). In the test of the effect of different treatments in preventing the growth of pathogenic fungal mycelium, a concentration of 60 ppm of metalaxyl-mancozeb fungicide with 96.32% had the highest effect in the control of the pathogen, but also concentration of 5 ppm of fossil aluminum with a rate of 12.30% had the lowest effect. . In present reserch metalaxyl-mancozeb fungicide 150 ppm by 88.60% inhibition of the pathogen and fusitel aluminum fungicide 150 ppm by 79.37% reduction of disease in the greenhouse were the best treatments during study. These results showed that to increase the effectiveness of this essential oil, it is necessary to use a higher concentration of essential oil compared to the chemical compounds studied in this study.
Conclusion: According to the results of this study, thyme essential oil has a high potential both in terms of antifungal power and induction of plant defense mechanisms against plant pathogens. However, the results of parametric analysis as well as analysis of variance showed that, compared to chemical compounds, higher concentrations of plant essential oils should be used to combat this disease.