اثر برخي تركيبات فرار القاءكننده مقاومت بر كنترل بيماري برق‌زدگي نخود

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

بيماري برق‌زدگي نخود با عامل قارچي Ascochyta rabiei (Pass.) Lab. از مهم‌ترين عوامل محدودكننده توليد نخود در بيش‌تر مناطق جهان است. در اين پژوهش اثر شش تركيب فرار القاءكننده مقاومت، شامل متيل‌ساليسيلات، 2،3- بوتان‌دي‌اُل، متيل‌جاسمونات، استوئين، ايندول و 3-پنتانول، در مقايسه با قارچكش كلروتالونيل بر رشد بيمارگر در آزمايشگاه و مهار بيماري برق‌زدگي و صفات رشدي نخود در گلخانه بررسي شد. كليه تركيبات فرار با غلظت 100 ميكرومولار از رشد ميسليومي بيمارگرA. rabiei جلوگيري نمودند و بيش‌ترين و كم‌ترين اثر بازدارندگي به مقدار 64/9 و 4/7 درصد به ترتيب مربوط به 3-پنتانول و متيل‌جاسمونات بود. در گلخانه، اين تركيبات فرار به‌جز متيل‌جاسمونات، سبب كاهش شدت بيماري برق‌زدگي نسبت به شاهد بيمار شدند. بيش‌ترين كاهش شدت بيماري مربوط به تيمار كلروتالونيل (86 درصد) و متيل‌ساليسيلات (55/8 درصد) بود. بيش‌تر تركيبات فرار در گياهان آلوده شده به بيمارگر، سبب افزايش وزن تَر و خشك ريشه و وزن تَر و خشك اندام هوايي نسبت به شاهد آلوده شدند. اثر متيل‌ساليسيلات بر افزايش وزن تَر اندام هوايي و اثر ايندول در افزايش وزن تَر و خشك ريشه و وزن خشك اندام هوايي نسبت به شاهد آلوده بيش از ساير تيمارها بود. متيل‌جاسمونات در مقايسه با ساير تركيبات فرار كم‌ترين اثر را بر افزايش صفات رشدي مورد بررسي داشت. استفاده از تركيبات فرار مي‌تواند به‌عنوان يك راهبرد جديد و نويدبخش جهت مديريت تلفيقي بيماري برق‌زدگي نخود و تحريك رشد اين گياه در نظر گرفته شود.

Background and Objectives Chickpea (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 Methods First, six volatile compounds including methyl salicylate, 2,3-butanediol, methyl-jasmonate, acetoin, indole and 3-pentanol 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 five-millimeter 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%. Results All volatile compounds inhibited the mycelial growth of A. rabiei on CDA with the highest (64.91%) and lowest (4.67%) inhibition obtained by 3-pentanol 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 3-pentanol 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. Discussion The 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.