تحمل به یخ‌زدگی اکوتیپ‏های سیر (allium sativum l.) تحت تاثیر تاریخ کاشت در شرایط کنترل‌شده

سیر گیاهی دارویی و سرمادوست است اما در مورد میزان تحمل به سرمای آن اطلاعات چندانی در دسترس نمی‌باشد. این آزمایش به‌منظور بررسی میزان تحمل اکوتیپ‎های مختلف این گیاه به تنش یخ‏زدگی، در سال 1391 در دانشکده کشاورزی دانشگاه فردوسی مشهد، به‌صورت فاکتوریل در قالب طرح پایه کاملاً تصادفی با چهار تکرار، اجرا شد. فاکتورهای آزمایش شامل چهار اکوتیپ سیر (بجنورد، تربت حیدریه، خواف و نیشابور)، هشت دمای یخ‏زدگی (دمای صفر (شاهد)، 3-، 6-، 9-، 12-، 15-، 18- و 21-درجه سانتی‏گراد) و دو تاریخ کاشت (28 شهریور و 30 مهر) بودند. برای این منظور گیاهان کشت شده در گلدان در فضای آزاد جهت خوسرمایی رشد یافته و سپس به فریزر ترموگرادیان منتقل شدند. سه هفته پس از اعمال دماهای یخ‏زدگی درصد بقاء، دمای کشنده 50 درصد گیاهان براساس درصد بقاء (lt50su)، ارتفاع، سطح برگ، دمای کاهنده 50 درصد سطح برگ (rlat50)، وزن خشک و دمای کاهنده 50 درصد وزن خشک (rdmt50) تعیین شدند. نتایج نشان داد اثر متقابل تاریخ کاشت، اکوتیپ و دماهای یخ‏زدگی بر درصد بقاء، ارتفاع، سطح برگ و وزن خشک در پایان دوره بازیافت معنی‏دار بود. با وجود این‌که در کاشت اول تنها دو اکوتیپ بجنورد و تربت حیدریه قادر به تحمل دمای 15 درجه سانتی‏گراد بودند اما در کاشت دوم دو اکوتیپ تربت حیدریه و نیشابور در دمای ذکر شده به‌ترتیب متحمل 40 و 33 درصد تلفات گیاهی شدند در حالی‌که اکوتیپ‏های خواف و بجنورد از حداکثر بقاء برخوردار بودند. lt50suدر اکوتیپ‏های بجنورد و تربت حیدریه در کاشت اول کمتر از کاشت دوم بود، اما در اکوتیپ‏های نیشابور و خواف، گیاهان کاشت دوم نسبت به کاشت اول lt50su کمتری داشتند. سطح برگ اکوتیپ‏های تربت حیدریه، خواف و نیشابور در کاشت دوم نسبت به کاشت اول افزایش بیشتری داشتند، در حالی‌که اکوتیپ بجنورد در کاشت اول دارای بیشترین سطح برگ بود. در هر دو تاریخ کاشت کمترین rlat50 و rdmt50 را اکوتیپ بجنورد به خود اختصاص داد، در صورتی‌که در کاشت اول بیشترین مقدار این دو شاخص در اکوتیپ خواف مشاهده شد. همبستگی بالایی بین rlat50و rdmt50 با lt50su(به‌ترتیب**0.98=r و **0.90=r) وجود داشت و لذا به نظر می‏رسد که می‏توان از این شاخص‏ها برای ارزیابی تحمل به یخ‌زدگی سیر استفاده کرد. بررسی تحمل به سرمای سیر در شرایط مزرعه، جهت بررسی همبستگی احتمالی بین نتایج آن با شرایط کنترل‌شده سودمند خواهد بود.

Freezing Tolerance of Garlic Ecotypes (Allium sativum L.) under Controlled Conditions

Introduction;Garlic is a medicinal and cool season plant, but there is not much information on its level of cold tolerance. Khorasan province is one of the suitable areas for growing garlic. The conventional planting date of garlic in this region takes place between 6 October and 5 December. Available evidences shows that garlic plants have been affected by cold stress due to inappropriate planting date. Some researchers have recommended the use of controlled freezing tests as a suitable approach to assess cold tolerance of plants. In this regard, it is stated that LT50su in wheat had the highest correlation with field survival index when the crown was exposed to cold stress. The present experiment was conducted to study cold tolerance and understanding the most critical growth stages of garlic ecotypes to cold stress under controlled conditions.;Materials and Methods;This experiment was conducted as a factorial based on completely randomized design with four replications in Agricultural Faculty of Ferdowsi University of Mashhad during 2012. The experimental factors included two levels of planting date (18 September and 21 October), garlic ecotype in four levels (Bojnurd, Torbate Heydarieh, Neyshabur and Khaf) and eight levels of freezing temperature (0, 3, 6, 9, 12, 15, 18 and 21°C). Plants that grown in outside conditions and acclimated to cold temperatures were transferred to the thermogradient freezer to apply cold stress. Survival percentage, Lethal Temperature 50% mortality according to the survival percentage (LT50su), plant height, leaf area, reduced leaf area temperature 50 (RLAT50), dry weight and reduced dry matter temperature 50 (RDMT50) were determined at three weeks after applying the stress.;Results and Discussion;In the first planting date, the survival of Bojnurd and Torbate Heydarieh ecotypes decreased 20% and 26% at 15 °C compared with zero temperature, respectively, while two other ecotypes disappeared at this temperature. In the second planting date, Khaf and Bojnurd ecotypes had a good survival at 15 °C while Neyshabur and Torbate Heydarieh ecotypes disappeared 60 and 67% at this temperature, respectively. Since the growth stage has an effect on cold acclimation and stress tolerance, this response can be due to difference in the growth stage of plants. However, this reaction was different depending on the ecotypes. With changing planting date from September to October, LT50su decreased 9.6 and 6 °C in Khaf and Neysabur ecotypes, and increased 3.9 and 2 °C in Bojnurd and Torbate Heydarieh ecotypes, respectively. In the first planting date with decreasing temperature from zero to 18 °C, the maximum and minimum decrease in height (90 and 27%) were observed in Torbate Heydarieh and Bojnurd ecotypes, and Neyshabur and Khaf ecotypes disappeared at this temperature. Also, in the second planting date with decreasing temperature from zero to 15 °C, plant height decreased 47, 52 and 30% in Khaf, Torbate Heydarieh and Neyshabur ecotypes, respectively. However, plants height of Bojnurd ecotype decreased only 4% under similar conditions. In the first planting date Bojnurd and Torbate Heydarieh ecotypes had the lowest decrease in leaf area (about 3 and 17%, respectively) at 12 °C compared with zero temperature, while Khaf and Neyshabur ecotypes assigned to themselves the highest decrease in leaf area (about 85 and 58%, respectively). Also, in the second planting date leaf area of Bojnurd ecotype decreased 18% at 15 °C compared with zero temperature, while in similar conditions Torbate Heydarieh, Khaf and Neyshabur ecotypes had 56, 38 and 58% decrease in leaf area, respectively. The lowest decrease in dry matter percentage was observed in Neyshabur (23%) and Bojnurd (22%) ecotypes in the first and second planting date, respectively, following decreasing temperature to 12 °C. Studies have shown that plants with faster growth before the frost were more sensitive to cold temperatures and as a result, damaged more. So, it seems that increasing growth of Khaf and Neyshabur ecotypes and their progress towards more advanced growth stages reduced cold tolerance of these plants in the first planting date.;  ;Conclusions ;Freezing stress decreased survival percentage and recovery of garlic ecotypes. In the first planting date Bojnurd and Torbate Heydarieh ecotypes had a better survival percentage and Khaf and Neyshabur ecotypes had lower survival percentage while in the second planting date Khaf and Neyshabur ecotypes had higher survival percentage than Bojnurd and Torbate Heydarieh ecotypes. Also, results of LT50su indicated that Bojnurd and Khaf ecotypes had higher freezing tolerance in the first and second planting date, respectively. Different reactions of garlic ecotypes at various stages of stress may be due to their genetic characteristics and geographic origin. In terms of recovery (height, leaf area and dry weight), the plants of the second planting date had more height and dry matter, as well. Based on the RDMT50 and RLAT50, moreover, Bojnurd ecotype in both planting date and Khaf ecotype in the first planting date were recognized as most tolerant and sensitive ecotypes, respectively.