بررسی خصوصیات رشدی چند گونه شبدر (trifolium spp.) تحت تاثیر تنش یخ‌زدگی در شرایط کنترل‌شده

به‌منظور بررسی تحمل به تنش یخ‌زدگی و ویژگی‌های رشدی چند گونه شبدر (trifolium spp.) پس از اعمال تنش مذکور در شرایط کنترل‌شده، آزمایشی در سال زراعی 92-1391 در دانشکده کشاورزی دانشگاه فردوسی مشهد به‌صورت فاکتوریل در قالب طرح کاملاً تصادفی با چهار تکرار اجرا شد. عوامل آزمایش شامل تاریخ کاشت (28 شهریور و 27 مهر)، گونه‌های شبدر (قرمز t. pratense، سفید t. repense، ایرانی t. resupinatum(گونه‌های پاییزه) و شبدر لاکی t. incarnatum(گونه بهاره)) و دماهای یخ‌زدگی (صفر (شاهد)، 3-، 6-، 9-، 12-، 15-، 18-و 21 -درجه سانتی‌گراد) بودند. در پایان دوره بازیافت درصد بقاء، دمای کشنده 50 درصد گیاهان بر اساس درصد بقاء (lt50su)، سطح برگ و دمای کاهنده 50 درصد سطح برگ (rlat50)، وزن خشک و دمای کاهنده 50 درصد وزن خشک (rdmt50) مورد بررسی قرار گرفت. نتایج نشان داد که با کاهش دما از صفر به 15 -درجه سانتی‌گراد در تاریخ کاشت 28 شهریور، گونه قرمز و ایرانی از درصد بقاء بالاتری برخوردار بودند. همچنین این گونه‌ها در تاریخ کاشت 28 شهریور lt50su کمتری داشتند در صورتی‌که در تاریخ کاشت 27 مهر گونه لاکی lt50su کمتری داشت و شبدر سفید از نظر صفت مذکور، در هر دو تاریخ کاشت تقریباً مشابه بود. برهمکنش تاریخ کاشت، گونه و دماهای یخ‌زدگی بر سطح برگ و وزن خشک بوته در پایان دوره بازیافت معنی‌دار بود. در تاریخ کاشت 28 شهریور شبدر ایرانی در دمای 18- درجه سانتی‌گراد نسبت به دمای صفر درجه سانتی‌گراد کمترین کاهش سطح برگ را داشت و در تاریخ کاشت 27 مهر نیز برخلاف سایر گونه‌ها در دمای 15- درجه سانتی‌گراد نسبت به تیمار شاهد سطح برگ آن افزایش داشت. در کاشت 28 شهریور در دمای 18 -درجه سانتی‌گراد گونه‌های قرمز و ایرانی درصد بقاء بالاتری نسبت به گونه‌های سفید و لاکی داشتند. دو گونه شبدر ایرانی و سفید در هر دو تاریخ کاشت 28 شهریور و 27 مهر، به‌ترتیب کمترین و بیشترین rdmt50 را داشتند.

Evaluation of Growth Characteristics of Four Clover Species (Trifoliums pp.) Affected by Freezing Stress under Controlled Conditions

Introduction: In Iran, clover is the second most important forage crop after alfalfa (Medicago sativa) and is cultivated on a surface of about 70,000 hectares. Yield improvement of this plant could be achieved through autumn cultivation. Iran is still one of the main centers for the diversity of clover species, there is not much information about freezing tolerance of native species of this important plant. Since freezing stress is one of the most important winter stresses which causes severe damage to the plant cells and tissues and ultimately plant death, evaluation of freezing tolerance of this crop could help to determination of the best planting date in order to achieve the highest yield. The aim of this study was to evaluate the freezing tolerance of four clover species through assessment of plant survival and regrowth after freezing stress. Materials and Methods: In order to study growth criteria of four clover species after freezing stress in controlled conditions, an experiment was conducted in 201213 in Faculty of agriculture, Ferdowsi University of Mashhad. Treatments were arranged as factorial based on Completely Randomized Design with four replications. Factors were included of planting dates (late September and late October), clover species (red clover T. pratense, white clover T. repense, Persian clover T. resupinatum (autumn species) and crimson clover T. incarnatum (spring species) and freezing temperatures (0 (control), 3, 6, 9, 12, 15, 18, 21ºC). Survival percentage, LT50 according to Survival (LT50su), leaf area, Reduced 50% Leaf Area Temperature (RLAT50), dry weight and Reduced Dry Matter Temperature 50 (RDMT50) were measured after three weeks regrowth. Results and Discussion: Results indicated that survival percentage was significantly affected by interaction of planting date, species and freezing temperatures. In both planting dates, crimson and white species showed a good survival till 15°C while they were killed as temperature was more decreased to 18°C. In first planting date, two species of red and Persian clover had 50 and 42% survival, but were killed in this temperature in the second planting date. The lowest LT50su in autumn (red, white and Persian) and spring (crimson) species was found in first and second planting dates, respectively indicating higher freezing tolerance in crimson species at second planting date and a better acclimation of autumn species at first planting date which led to a higher survival compared to spring species. Leaf area was significantly affected by planting date, species and freezing temperatures at the end of the recovery period. In first planting date, decreasing temperature from zero to 18°C caused reduction of 98 and 48% of leaf area in red and Persian species while no plant of white and crimson species was survived in this condition. In second planting date, leaf area was decreased about 6, 33 and 2% as temperature decreased from zero to 15°C while leaf area of Persian species, not only was not decreased, but also increased by about 12%. The lowest and highest RLAT50 were observed in Persian and red species. Interaction of planting date and species on RDMT50 was significant in a way that in delayed planting date, RDMT50 was increased in red, Persian and crimson species while it was decreased in white species. Conclusion: Red and Persian species showed higher freezing tolerance according to indices of survival percentage and LT50su. The highest recovery ability of plants based on leaf area per plant, RLAT50, plant dry matter and RDMT50 was found for second planting date. Also annual species of Persian and crimson had lower RLAT50 and RDMT50 and higher freezing tolerance compared to perennial species of red and white clover.