اثر برخی ترکیبات فرار القاء‏کننده مقاومت بر کنترل بیماری برق‌زدگی نخود

بیماری برق‌زدگی نخود با عامل قارچی ascochyta rabiei (pass.) lab. از مهم‌ترین عوامل محدودکننده تولید نخود در بیش‌تر مناطق جهان است. در این پژوهش اثر شش ترکیب فرار القاء‏کننده مقاومت، شامل متیل‌سالیسیلات، 2،3 بوتان‌دی‌اُل، متیل‌جاسمونات، استوئین، ایندول و 3پنتانول، در مقایسه با قارچ‏کش کلروتالونیل بر رشد بیمارگر در آزمایشگاه و مهار بیماری برق‌زدگی و صفات رشدی نخود در گلخانه بررسی شد. کلیه ترکیبات فرار با غلظت 100 میکرومولار از رشد میسلیومی بیمارگرa. rabiei جلوگیری نمودند و بیش‌ترین و کم‌ترین اثر بازدارندگی به مقدار 9/64 و 7/4 درصد به ترتیب مربوط به 3پنتانول و متیل‌جاسمونات بود. در گلخانه، این ترکیبات فرار به‌جز متیل‌جاسمونات، سبب کاهش شدت بیماری برق‌زدگی نسبت به شاهد بیمار شدند. بیش‌ترین کاهش شدت بیماری مربوط به تیمار کلروتالونیل (86 درصد) و متیل‌سالیسیلات (8/55 درصد) بود. بیش‌تر ترکیبات فرار در گیاهان آلوده ‏شده به بیمارگر، سبب افزایش وزن تَر و خشک ریشه و وزن تَر و خشک اندام هوایی نسبت به شاهد آلوده شدند. اثر متیل‌سالیسیلات بر افزایش وزن تَر اندام هوایی و اثر ایندول در افزایش وزن تَر و خشک ریشه و وزن خشک اندام هوایی نسبت به شاهد آلوده بیش از سایر تیمارها بود. متیل‌جاسمونات در مقایسه با سایر ترکیبات فرار کم‌ترین اثر را بر افزایش صفات رشدی مورد بررسی داشت. استفاده از ترکیبات فرار می‌تواند به‌عنوان یک راهبرد جدید و نویدبخش جهت مدیریت تلفیقی بیماری برق‌زدگی نخود و تحریک رشد این گیاه در نظر گرفته شود.

The effect of some defense inducing volatile compounds against chickpea Ascochyta blight

Background and ObjectivesChickpea (Cicer arietinum L.) is the third most important legume crop in the world. Ascochyta blight caused by Ascochyta rabiei (Pass.) Lab. is one of the most important threats for producing chickpea in most of the growing areas. The pathogen invades all aerial parts of the plant and causes severe yield and quality losses. The present study aims to evaluate the effect of some defense inducing volatile compounds in inhibiting A. rabiei, as well as the effect of these compounds on some chickpea growth traits at the presence of the pathogen.Materials and MethodsFirst, six volatile compounds including methyl salicylate, 2,3butanediol, methyljasmonate, acetoin, indole and 3pentanol were prepared in sterile distilled water (100 μM) containing 0.2% Tween 20, and were used for laboratory and greenhouse studies. The in vitro antifungal activity of volatile compounds was tested on chickpea seed meal dextrose agar (CDA) medium. Then, a fivemillimeter agar disk containing the mycelium of the pathogen was placed on the surface of CDA medium in 9 cm diameter Petri dishes. The Petri dishes were inverted and 100 μl of the emulsion of each volatile compound was placed inside the lid. The Petri dishes were sealed and kept at the same inverted position to avoid the dropping of volatile compounds over the culture medium. A greenhouse experiment with nine treatments (including six volatile compounds, chlorothalonil fungicide, healthy and diseased controls) was conducted in a completely randomized design. In addition, the emulsions of volatile compounds were sprayed on the leaf surfaces 12 days after sowing chickpea seeds (variety Bivanij). After 48 hours, the conidial suspension of the pathogen in water (2 x 104 conidia/mL) was sprayed to the surface of chickpea seedlings. Disease severity and plant growth indices including shoot fresh weight, shoot dry weight, root fresh weight and root dry weight were measured two weeks after inoculation. Statistical analyses were performed by SAS software (version 9.3). The means were compared by Duncan’s test at a statistical probability level of 5%.ResultsAll volatile compounds inhibited the mycelial growth of A. rabiei on CDA with the highest (64.91%) and lowest (4.67%) inhibition obtained by 3pentanol and methyl jasmonate, respectively. In the greenhouse test, all volatile compounds, except methyl jasmonate, reduced the incidence of blight symptoms compared to the diseased control. The highest disease reduction was obtained by chlorothalonil (86.04%) and methyl salicylate (55.81%). At the presence of the pathogen, all volatile compounds increased root fresh weight, root dry weight and shoot fresh weight, and increased shoot dry weight with the exception of 3pentanol and methyl jasmonate. Compared to the diseased control, the effect of indole on root fresh and dry weight and shoot dry weight, as well as the effect of methyl salicylate on shoot fresh weight was more than other compounds. Methyl jasmonate had the least improving effect on growth traits compared to other volatile compounds.DiscussionThe volatile compounds used in this study inhibited A. rabiei in both in vitro and greenhouse tests. They also improved chickpea growth parameters at the presence of the pathogen. The use of volatile compounds could be considered as a new and promising strategy for the integrated management of Ascochyta blight.