ارزيابي تحمل به خشكي چهار رقم كلزا (.Brassica napus L) براساس خصوصيات فيزيولوژيكي و بيوشيميايي

Evaluation of Physiological and Biochemical Characteristics of Four Canola (Brassica napus L.) Cultivars in drought condition

به‌منظور بررسی اثر تنش خشكی در مرحله گل‌دهی بر عملكرد و صفات فیزیولوژیك، مورفولوژیك و بیوشیمیایی گیاه كلزا، آزمایشی، در مزرعه پژوهشی مركز تحقیقات كشاورزی و منابع طبیعی یزد طی سال زراعی 91-1390 انجام شد. آزمایش به‌صورت كرت‌های خرد شده در قالب طرح پایه بلوك‌های كامل تصادفی با سه تكرار انجام شد. نمونه‌برداری از گیاهان 7، 12 و 26 روز پس از اعمال تنش انجام شد. آبیاری به‌عنوان عامل اصلی در دو سطح به‌صورت آبیاری معمولی یا شاهد (آبیاری پس از 80 میلی‌متر تبخیر از تشتك كلاس A) و تنش در مرحله گل‌دهی (آبیاری پس از 160 میلی‌متر تبخیر از تشتك كلاس A) و ارقام (Oise، Triangle، Karun و SLM046) در چهار سطح به‌عنوان عامل فرعی در نظر گرفته شدند. نتایج نشان داد كه تنش خشكی موجب كاهش معنی‌دار محتوای نسبی آب برگ و هدایت روزنه‌ای در كلیه ارقام مورد مطالعه كلزا گردید، در حالی‌كه محتوای قندهای محلول، پرولین و عدد كلروفیل در اثر تنش خشكی افزایش یافت. در بین ارقام مورد بررسی ژنوتیپ SLM046 از نظر صفات عملكرد، وزن هزار‌دانه، تعداد غلاف در بوته، محتوای نسبی آب برگ و هدایت روزنه‌ای به سایر ارقام برتری داشت و در مقایسه با سایر ارقام نسبت به تنش خشكی متحمل‌تر بود. رقم SLM046 بالاترین و رقم Karun كم‌ترین عملكرد (به‌ترتیب با 2553 و 2178 كیلوگرم در هكتار) را در شرایط تنش به‌خود اختصاص دادند.

Introduction Rapeseed (Brassica napus L.) is one of the major crops cultivated mainly for oil, human consumption and renewable fuel all over the world. Drought stress is one of the most important abiotic factors which adversely affect growth, metabolism and yield of crops in semiarid and arid area. Drought stress during any particular growth stage of crops causes yield reduction. In order to evaluate the effect of drought stress on yield, physiological, morphological and biochemical characteristics of rapeseed in flowering stage, this field experiment was carried out in Yazd agricultural research institute during 2011-2012. Materials and Methods The experiment was conducted in split-plot design based on randomized complete blocks with three replications imposed. Irrigation was considered as the main plot at two levels including control (irrigation after 80 mm evaporation from class A pan) and stress in the anthesis stage (irrigation after 160 mm evaporation from class A pan) and cultivars (Oise, Triangle, Karun and SLM046) were considered as sub plots. Sampling was carried out 7, 12 and 26 days after drought stress imposed. In each plot, 7, 12 and 26 days after stop irrigation from flowering stage (drought stress treatment), 4-5 expanded leaves from above of canopy were harvested. Relative water content of leaves and stomatal conductance were recorded. Soluble carbohydrate and proline content were measured. The lipid peroxidation level of the leaves was determined by measuring the content of malondealdehyde. Yield and yield components (number of grains per pod, number of pod per plant and weight of 1000 grains) were recorded at maturity. Results and Discussion The results showed that drought and cultivar interaction on SPAD value was not significant after stress. The interaction of the drought on leaf relative water content was significant at 26 days after the stress. The results revealed that, drought stress led to a significant decrease in relative water content of leaves and stomata conductance in all cultivars. However, soluble carbohydrates and proline were increased after stress application. The interaction of drought on soluble carbohydrate was significant at 26 days after the stress. Interaction of treatments on leaf proline content in each sampling period was significant. The highest content of proline was observed in SLM046 (11.76 mM g-1 fresh weight) and the lowest proline content was observed in Oise cultivar (6.01 mM g-1 fresh weight). MDA content was increased in stress conditions. The highest MDA content was observed in Oise cultivar (1.15 µM g-1 fresh weight) 26 days after the stress and the lowest MDA observed in SLM046 cultivar (0.695 µM g-1 fresh weight) 7days after the stress. Analysis of variance for yield and yield components under irrigation regimes showed that, interaction of treatments on grain yield and weight of 1000 grains was significant. Triangle and SLM046 cultivars had higher grain yield in compare to the other cultivars. SLM046 exhibited the highest stress tolerance and also contained the highest yield, grain weight, number of pod per plant, relative water content and stomata conductance among all the cultivars. In addition, the highest and the lowest yield were observed in cultivars SLM046 and Karun (2553and 2178 kg ha-1, respectively), following stress application. Water deficit stress on canola decreased the number of pods per plant and the number of grains per pod. Conclusions Occurrence of drought stress during flowering reduced the number of grains per pod and canola yield. The results showed that, there was significant difference between cultivars for crop yield, weight of thousands grains, relative water content, stomata conductance, proline and carbohydrate content. Increased carbohydrate and proline content as osmolites caused lower cell water potential. The cultivars had different response to drought stress and the the highest yield and RWC were observed in SLM046 cultivar. Sugar and proline in the cell, the cell water potential decreased. The drought tolerance of SLM046 was better than other cultivars and had the highest yield and Relative water content.