مطالعه اثر ضدباکتریایی چند اسانس گیاهی در کنترل باکتری Pectobacterium carotovorum subsp. carotovorum عامل بیماری پوسیدگی نرم سیب زمینی

Pectobacterium carotovorum subsp. carotovorum (Pcc) is the causal agent of soft rot on potato tubers that has a wide host range and causes disease on many plants. This bacterium has the ability to secrete extracellular enzymes such as pectate lyase, polygalacturonase, and cellulase, which can degrade plant tissues and cause decay and soft rot. The highest damage to potato occurs after harvest and during storage period. This bacterium is more harmful in wet areas and existence of moisture is an important factor for disease development. The first report of the disease in Iran on potato as the most important and economical host was from Fars province in 1998. Increasing resistance of pests and pathogens to chemical pesticides has leaded researchers to new control methods. One of these methods is use of plant secondary metabolites and many studies are under way in this area. In the present study, effect of essential oils of nine medicinal plants (Anise, Shirazi thyme, Barije, Orange, Tarragon, Ajwain, Khuzestani savory, Myrtle and Clove) is investigated on a standard strain of Pcc, two native strains and a standard strain of Escherichia coli according to Clinical and Laboratory Standards Institute (CLSI) principles. At the initial screening stage, antimicrobial activity of mentioned EOs at 10 mg concentration is evaluated using disk diffusion method in petri dishes containing 24-hour suspension of the bacteria (OD600 = 0.3). The results showed that all of the EOs have inhibitory effects on tested bacteria, however, Khuzestani savory, Shirazi thyme and Ajwain EOs with average inhibition zone diameter of 7.2, 6.9 and 5.3 for Pcc strains, and 4.1, 3.9 and 3.4 cm for E. coli, respectively, had the most inhibition effect. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the three representative oils were also determined on studied bacteria that the mean values on Pcc strains are recorded 150 µg in both asaays for Khuzestani savory, 150 and 300 µg for Shirazi thyme and 1250 and 2500 µg for Ajwain EOs. For E. coli, these values are measured 150 and 300 µg for Khuzestani savory, 300 and 600 µg for Shirazi thyme, and 2500 µg for in both assays for Ajwain EOs, respectively. All experiments are carried out in triple with five replicates. The results show that these oils have significant efficiency at very low concentrations for Pcc control and can be used as suitable alternatives for chemical pesticides in order to manage the disease.