ارزيابي تحمل به خشكي اكوتيپ هاي يونجه (Medicago sativa) با استفاده از شاخص هاي تحمل به خشكي

Evaluation of drought tolerance in alfalfa (Medicago sativa) ecotypes using drought tolerance indices

خشكي از تنش هاي محيطي مهم در كاهش رشد و توليد گياهان مي باشد. اين بررسي به منظور ارزيابي تحمل به خشكي اكوتيپ هاي يونجه با استفاده از شاخص هاي تحمل به خشكي طي سال هاي زراعي 88-1387، در ايستگاه تحقيقات كشاورزي و منابع طبيعي نيشابور اجرا شد. آزمايش به صورت كرت هاي خرد شده در قالب طرح بلوك هاي كامل تصادفي با سه تكرار انجام شد. كرت هاي اصلي به سه تيمار عدم تنش، تنش ملايم و تنش شديد (دور آبياري 7، 10 و 14 روز) و كرت هاي فرعي به 11 اكوتيپ يونجه اختصاص داشتند. شاخص هاي تحمل به تنش (STI)، تحمل به خشكي (TOL)، حساسيت به تنش (SSI)، ميانگين هندسي توليد (GMP)، ميانگين حسابي توليد (MP) و ميانگين هارمونيك (HARM)، با استفاده از عملكرد علوفه خشك در شرايط تنش (Ys) و بدون تنش(Yp) محاسبه شدند. همبستگي مثبت و معني دار بين عملكرد علوفه خشك در شرايط تنش و عدم تنش و شاخص ها نشان داد كه در تنش ملايم و شديد، شاخص هاي GMP، MP، HARM و STI مناسب ترين شاخص ها هستند (r2 = 0.97, p ? 0.01). با توجه به اين شاخص ها و مقادير Ys و Yp بالا و همچنين نمودار چند متغيره باي پلات مشخص شد كه اكوتيپ هاي قارقلوق و ملك كندي در تنش ملايم و فامنين در تنش شديد متحمل ترين اكوتيپ ها بودند. گروه بندي اكوتيپ ها نشان داد كه بر اساس عملكرد در شرايط تنش و بدون تنش و مقادير شاخص‌هاي انتخابي، آن‌ها در سه گروه حساس، متحمل و نيمه حساس به تنش قرار مي گيرند.

Risk of weather variability is amongst factors that always affect the cereal production in many areas. In order to determine the freezing tolerance of five barley (Hordeum vulgar L.) cultivars under controlled conditions, a factorial experiment based on CRD carried out with three replications at the crop physiology Laboratory of College of Agriculture, Ferdowsi University of Mashhad. Treatments were barley genotype with five levels, including Makouei, Karun×Kavir, lokht, Reyhan and Valfajr, and temperature in six levels (0, -4, -8, -12, -16 and -20 °C). Plants were kept under natural conditions until 4-6 leaf stage to provide the acclimation period and then were transferred to a thermo-gradient freezer to apply freezing stress. The cell membrane stability of genotypes was measured through electrolyte leakage (EL) and the LT50el (temperature for killing 50% of samples according to the electrolyte leakage) was also determined. Furthermore, survival percentage, plant height, dry weight, LT50su (temperature for killing 50% of samples according to survival) and RDMT50 (reduced dry matter temperature) were determined after three weeks recovery in the glasshouse. Results showed that leakage percentage from leaf and crown after freezing was significantly different (P < 0.01) amongst cultivars. The greatest (69.4) and the lowest (58.5) leakage percentage from leaf samples were observed in Valfajr and Karun×Kavir cultivars, respectively. Reyhan cultivar showed the highest (78.9) and Makouei, Karun×Kavir, lokht and Valfajr cultivars showed the lowest leakage percentage from crown samples. Plant height, dry weight and LT50su of cultivars were significantly different after freezing. For instance, the dry weight of plants after three weeks recovery was 978 and 480 mg/plant for Karun×Kavir and Valfajr cultivars, respectively. Most studied traits were significantly reduced under temperatures lower than -12oC compared to the control.