بررسی اثر تنش خشکی بر عملکرد روغن و ترکیب اسیدهای چرب دانه در ارقام کلزا (.Brassica Napus L)

این تحقیق به‌منظور بررسی تاثیر تنش خشکی بر عملکرد روغن و ترکیب اسیدهای چرب کلزا انجام شد. آزمایش به‌صورت کرت‌های خرد شده در قالب طرح بلوک‎های کامل تصادفی با 3 تکرار انجام شد. در این طرح، تیمار آبیاری در کرت اصلی در سه سطح شامل تیمار شاهد (آبیاری بعد از 80 میلی‌متر تبخیر از سطح تشتک تبخیر)، قطع آبیاری از مرحله گل‌دهی و قطع آبیاری از مرحله خورجین‌دهی و 6 رقم کلزا که در کرت فرعی قرار گرفتند. نتایج نشان داد که اثر تنش خشکی بر محتوای اسید پالمیتیک، اسید استئاریک، اسید لینولئیک و اسید مریستیک معنی‌دار است و برای سایر اسیدهای چرب و درصد روغن اثر تنش خشکی معنی‌دار نبود. بین ارقام مورد بررسی، از نظر درصد روغن دانه، درصد اسید استئاریک، اسید اولئیک و اسید لینولئیک تفاوت معنی‌داری وجود داشت که این موضوع نشان داد در بین ارقام کلزا از نظر درصد روغن‌دانه و درصد اسیدهای چرب تنوع وجود دارد. فراوان‌ترین ترکیب اسیدهای چرب در این تحقیق مربوط به اسید چرب تک غیر‌اشباع اسید اولئیک (67.96 درصد) و اسیدهای چرب چند غیراشباع، شامل اسید لینولئیک (7.21 درصد) و اسید لینولنیک (8.75 درصد) بود. نتایج نشان داد که تنش خشکی باعث کاهش معنی‌دار عملکرد شده ولی تاثیر چندانی بر درصد روغن دانه نداشته است. براساس نتایج درصد کل اسیدهای چرب اشباع در هر دو شرایط قطع آبیاری (مرحله گل‌دهی و خورجین‌دهی) کاهش معنی‌داری را نشان داده است. اما تغییرات درصد کل اسیدهای چرب غیراشباع در هر دو شرایط تنش معنی‌دار نبود. ولی در مجموع نسبت درصد کل اسیدهای چرب غیر‌اشباع به درصد کل اسیدهای چرب اشباع (tu/ts) افزایش معنی‌داری را نشان داد. بیش‌ترین مقدار اسید اولئیک، درصد روغن دانه و عملکرد روغن دانه در شرایط بدون‌تنش و تنش خشکی مربوط به رقم lilian بود. بنابراین lilian با عملکردی بیشتر از متوسط کل، رقمی مناسب در برنامه اصلاحی می‌تواند باشد.

Evaluation of drought stress effect on seed oil yield and fatty acid composition in canola (Brassica napus L.) cultivars

IntroductionOilseed crops with a high relative amount of unsaturated fatty acids content are one of great significance for human health. Canola oil is considered one of the most healthpromoting vegetable oils in terms of unsaturated fatty acid. Seed fatty acid composition and oil content of canola are also affected by drought stress. Large parts of the world are increasingly affected by drought. Drought stress is one of the most important abiotic factors which adversely affect growth, metabolism and yield of crops worldwide. In many parts of the Iran, canola is grown under rainfed conditions. Plant response to moisture stress has a negative effect on grain yield, which decreases significantly as a result of drought stress. Drought stress during flowering and seedfill stages can alter oil contents and fatty acid compositions of canola seed. The present experiment studied the effect of drought stress on oil contents and fatty acid composition in canola genotypes at water stress under endofseason drought (flowering and siliquing stages). Materials and methodsThe experiment was conducted as split plot based on randomized complete block design with three replications. Irrigation regimes were considered as main plots and cultivars as subplots. Six winter canola cultivars including SLM046, Tassilo, Karun, Adriana, Cooper and Lilian were evaluated under irrigated and no irrigated. The irrigation regimes included: wellwatered (irrigation during full season), water deficit at flowering stage and water deficit at siliquing stage. Results and discussionsThe proportions (%) of fats (monounsaturated: polyunsaturated: saturated) in this study were approximately 68.0:26.0:6.0. The most abundant fatty acids in the current research were the oleic monounsaturated fatty acid (C18:1) and the polyunsaturated fatty acids, Linoleic acid (C18:2) and Linolenic acid (C18:3), in the proportions 67.96:17.21:8.75. The most abundant saturated fatty acid was Palmitic acid (C16:0), Stearic acid (18:0) and Myristic (14:0), in the proportions 3.87: 2.11: 0.044 % in samples. Based on analysis of variance, significant differences were observed between genotypes for oil yield (%), seed yield (kg ha1), Palmitic acid, Palmitolic acid, Stearic acid, Oleic acid, Linoleic acid, Linolenic acid, total saturated fatty acid (TSFA) and ratio of total unsaturated to total saturated fatty acid (TU/TS). The results of analysis of variance indicated that drought stress at flowering and siliquing stages significantly affected the amount of Myristic, Palmitic, Palmitolic, Stearic, Linoleic acids. The results showed that the highest and the lowest Oleic acid and seed oil percentage were found in Lilian and Tassilo genotypes, respectively. Also, the highest and the lowest palmitic and linoleic acids content belong to Tassilo and Lilian genotypes, respectively. These results suggest significant associations between Oleic acid with Palmitic and Linoleic acids. Oleic acid had significantly and negatively correlated with Palmitic acid, Linoleic acid and Linolenic acid, but it had a significant and positive correlation with oil content. Strong and negative correlation between oleic and Linoleic acid suggest significant connections among these fatty acids, as expected by their close biochemical association. Under wellwatered conditions (nonstress), the values of Palmitic, Myristic, Linoleic acids were significantly higher than drought stress at flowering (excepted for linoleic acid) and siliquing stages. At drought stress at flowering and siliquing stages, reduction in Palmitic acid content was 3.78 and 3.58%, in Myristic acid content was 17.06 and 21.67% and in Linoleic acid content was 2.24 and 3.44%, respectively. Under wellwatered conditions (nonstress), the value of TSFA was significantly higher than drought stress at flowering and siliquing stages. Whereas, water stress under endofseason drought increased TU/TS compared to the nonstress condition. ConclusionIn this study, the water stress under endofseason drought (flowering and siliquing stages) in canola crops considering fatty acid composition and seed oil stability has been studied. The changes in fatty acids composition in the present study were probably due to the combined effect of water deficits and high temperatures during the seedfilling period with the endofseason drought treatment (flowering and siliquing stages). This study showed that drought decreases slightly seed oil percentage, alters fatty acid composition and affects fatty acid composition stability. In addition, development of drought tolerant canola genotypes with stable high oleic and low Linolenic acid genes is critical to maintain the stability of oil production and desirable fatty acid composition. In conclusion, Further work is needed to determine the cause of alters in oleic and in fatty acids concentration, under drought stress in canola. The highest Oleic acid and seed oil percentage in nonstress and water stress under endofseason drought were found in Lilian genotype. Therefore, this genotype would be good parents in a breeding program to develop cultivars for stressed conditions, because their oil content remains unaffected but Oleic acid is increased by drought, thus improving the oil shelflife and quality. AcknowledgementThis study was conducted at the experimental farm of Agricultural Research Institute and Natural Resources, Yazd, Iran. The authors gratefully acknowledge the financial support from Agricultural Biotechnology Research Institute of Iran (ABRII), Karaj, Iran. Also, we are immensely grateful to the anonymous reviewers whose comments and suggestions have greatly helped in improving the standard of this manuscript.