بررسی غلظت‌های زیر بازدارندگی برخی اسانس‌های گیاهی بر فاکتورهای پرآزاری بیمارگر pseudomonas syringae pv. syringae

از بیماری‌های مهم باکتریایی درختان میوه، شانکر باکتریایی درختان هسته دار با عامل pseudomonas syringae pv. syringae (pss) می‌باشد. در این پژوهش، خصوصیات ضدباکتریایی شش اسانس گیاهی علیه باکتری pss براساس آزمون نشت در دیسک، تعیین حداقل غلظت بازدارنده و حداقل غلظت کشنده ارزیابی و گروه بندی شد. تاثیر غلظت زیربازدارندگی اسانس‌های منتخب بر برخی عوامل پر آزاری بیمارگر و نیز اثرگذاری اسانس های منتخب بر کاهش بیماری زایی باکتری روی میوه نارس گیلاس بررسی و ترکیبات اسانس ها مشخص گردید. براساس نتایج، اسانس مرزه خوزستانی و آویشن خراسانی اثر بازدارندگی قابل‌توجهی با حداقل غلظت بازدارندگی و کشندگی 1.16 و 2.32 گرم بر لیتر بر باکتری pss، در مقایسه با سایر اسانس ها و آنتی‍بیوتیک استرپتومایسین نشان دادند. اسانس های منتخب در غلظت زیر بازدارندگی از رشد بیمارگر جلوگیری نکردند. قابلیت تحرک توده ای سلول های تحت تیمار اسانس ها نسبت به شاهد 25 تا 55 درصد و قابلیت تحرک شناوری 18.42 تا 71/ 35 درصد کاهش یافت. آویشن خراسانی و مرزه خوزستانی با درصد بازدارندگی به ترتیب 75 و 70 درصد قوی‌ترین اثر مهارکنندگی را بر میزان تشکیل بیوفیلم نشان دادند. همچنین، در آزمون تولید توکسین، دو اسانس آویشن خراسانی و مرزه خوزستانی درکاهش تولید سیرینگومایسین و افزایش رشد قارچ geotrichum candidum به ترتیب به میزان 1.76 و 1.5 برابر در مقایسه با شاهد (عدم تیمار با اسانس) موثر بودند. تیمار اسانس ها در مقادیر حداقل غلظت بازدارنده سبب کاهش علائم بیماری شد. بر اساس آنالیز اسانس ها به ترتیب تیمول در اسانس آویشن خراسانی، کارواکرول در اسانس مرزه خوزستانی، پیپریتون در اسانس پونه کوهی و پولگون در اسانس کاکوتی به‌عنوان ترکیبات عمده تعیین شد. به‍طور کلی، نتایج این تحقیق نشان داد مواد موثره اصلی دو اسانس آویشن خراسانی و مرزه خوزستانی در کاهش فعالیت بیمارگر شانکر باکتریایی هسته داران موثر هستند که می توانند به عنوان ساختار شیمیایی الگو در جهت سنتز مواد ضدمیکروبی مد نظر قرار گیرند.

evaluation the sub-inhibitory concentrations of some plant essential oils on investigating factors of pseudomonas syringae pv. syringae

introduction one of the important bacterial diseases of stone-fruit trees is canker caused by pseudomonas syringae pv. syringae (pss). this pathogen employs a vast range of pathogenic and virulence factors during its interaction with its host in order to induce disease symptoms. to control the bacterial canker disease, various methods such as sanitary measures, selection of resistant cultivars and certified seedlings and chemical component based on copper are used. application pf plant derivatives such as essential oils and extracts, is one of the compatible management methods in line with environmental goals. essential oils include a wide range of antimicrobial components and have high efficacy, multiple mechanisms of action, and low toxicity on non-target organisms. the current study aimed to assess the inhibitory and sub-inhibitory effects of six indigenous medicinal essential oils against the causative agent of canker disease in stone fruits. the research evaluated the efficacy of these essential oils in reducing the virulence factors of the disease while identifying the active compounds within the oils. material and methodsthe antimicrobial properties of six native plant eos, namely thymus transcaspicus, satureja khuzistanica, mentha longifolia, ziziphora clinopodioides, perorkia abrotanoides, and artemisia persica were evaluated against pss bacteria based on disc diffusion assay test and measurement of minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc). moreover, the effect of essential oils on some virulence factors of pathogen including motility, biofilm, and syringomycine production was investigated in sub-inhibitory concentrations. the effect of selected eos on the reduction of bacterial pathogenicity on immature cherry fruitlets was also investigated. finally, the chemical composition of eos was determined using gas chromatography–mass spectrometry (gc-ms). results and discussionall studied essential oils have different antibacterial effects in interaction with pss bacteria. eos of t. transcaspicus and s. khuzistanica showed a significant inhibitory effect with minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) value of 1.16 and 2.32 g l-1, respectively against pss compared with other essential oils and streptomycin antibiotic. sub-inhibitory concentrations test of eos showed no significant effect on the growth pathogen. the swarming motility of bacterial cells treated with essential oil decreased by 25-55% and the swimming motility decreased by 18.42 to 35.71% compared with the control. t. transcaspicus and s. khuzistanica within the range of 70-75% showed the strongest inhibitory effect on biofilm formation. also, in the toxin production test, t. transcaspicus and s.khuzistanica eos are effective in reducing syringomycin production and increasing the growth of geotrichum candidum by 1.5 to 1.76 times compared with control (not treatment with eos). the eos treatment at mics reduced the symptoms of the disease. in immature cherries inoculated with pss bacterium and treated with eo of t. transcaspicus was not observed necrosis symptom. the four selected essential oils tested all had a role in reducing the virulence factors in pss, and the degree of effectiveness is different depending on the components of the essential oil. the higher the phenolic content in the essential oil, the greater its antimicrobial properties against plant pathogenic bacteria. according to the eos analysis, thymol in t. transcaspicus, carvacrol in s. khuzistanica, piperitone in m. longifolia, and pulegone in ziziphora clinopodioides were the major constituent compound. it seems that the highest amounts of compounds in essential oils have a higher antibacterial power. the eos of t. transcaspicus and s. khuzistanica effectively reduce the pathogenic activity of bacterial cankers agent in stone fruits. conclusionthe studied plant compounds in sub-inhibition concentration showed acceptable potential in inhibiting pathogenic agents in in vitro tests. taking into account the growing trend of the general acceptance of natural control compounds in the field of plant diseases, it seems that planning in line with how to use plant products to reduce the consumption of pesticides can be investigated and needs complementary experiments. in order to reduce the spread of bacterial canker symptoms and increase the life span of the tree, the main effective substances (oxygenated monoterpenes) of the essential oils of t. transcaspicus and s. khuzistanica can be used as a model chemical structure for the synthesis of antimicrobial substances using the experts in the field of chemistry and pharmaceuticals. it is suggested to investigate the stability and preservation of antimicrobial properties in laboratory and field conditions.