پديد آورندگان :
نظامي، احمد دانشگاه فردوسي مشهد - دانشكده كشاورزي - گروه زراعت و اصلاح نبات , ايزدي دربندي، ابراهيم دانشگاه فردوسي مشهد , جانعلي زاده قزويني، مريم دانشگاه فردوسي مشهد , حسن بيگي، روح الله دانشگاه فردوسي مشهد
چكيده فارسي :
به منظور بررسي تحمل به يخ زدگي خاكشير، آزمايشي به صورت فاكتوريل و در قالب طرح كاملاً تصادفي با سه تكرار در سال 1387 در دانشگاه فردوسي مشهد انجام شد. تيمارهاي آزمايش شامل اكوتيپ خاكشير (در پنج سطح شامل اقليد، سبزوار، همدان، تربت جام و نيشابور) و دماي يخ زدگي (در 10 سطح شامل صفر تا 18- با فواصل دو درجه سانتي گراد) بود. گياهان خاكشير در پاييز كشت و تا مرحله پنج تا هفت برگي در آب و هواي طبيعي رشد داده شدند. سپس براي اعمال دماهاي يخ زدگي به يك فريزر ترموگراديان منتقل شدند. سه هفته بعداز اعمال تنش، درصد بقاء، دماي پنجاه درصد كشندگي بر اساس درصد بقاء (LT50su)، تعداد برگ، دماي كاهنده 50 درصد تعداد برگ (RNLT50)، تعداد گره، دماي كاهنده 50 درصد تعداد گره (RNNT50)، وزن خشك و دماي كاهنده 50 درصد وزن خشك (RDMT50) آن ها بررسي شد. نتايج نشان داد اكوتيپ همدان بيشترين درصد بقاء و اكوتيپ نيشابور كمترين درصد بقاء را دارند. در اكوتيپ هاي اقليد و نيشابور كاهش معني دار درصد بقاء از دماهاي بالاتري (10- درجه سانتي گراد) نسبت به اكوتيپ هاي همدان، سبزوار و تربت جام (12- درجه سانتي گراد) شروع شد. در دماي 12- درجه سانتي گراد، اكوتيپ هاي نيشابور و تربت جام كمترين تعداد برگ واكوتيپ هاي همدان و اقليد به ترتيب بيشترين و كمترين وزن خشك زيست توده را بعد از دوره بازيافت دارا بودند. همچنين در دماي 12- درجه سانتي گراد، تعداد گره در اكوتيپ همدان تقريباً 30 درصد نسبت به شاهد كاهش يافت، درحالي كه اين كاهش در اكوتيپ هاي اقليد و نيشابور بسيار بيشتر بود. در اين آزمايش LT50su بين 10.2- تا 12.1- درجه سانتي گراد متغير بود. رتبه بندي اكوتيپ هاي خاكشير بر اساس شاخص هاي LT50su، RNLT50، RNNT50 و RDMT50 نشان داد كه اكوتيپ هاي نيشابور و همدان به ترتيب حساس ترين و متحمل ترين اكوتيپ هاي خاكشير نسبت به تنش يخ زدگي بودند
چكيده لاتين :
Introduction
Flixweed is an annual dicotyledonous winter herb from Cruciferae (Brassicaceae) family which grows in many countries of the world. In Iran it is seen in many of wheat and canola producing regions. Flixweed is used for healing a variety of diseases such as measles and smallpox, cough, asthma, edema and tumor. It also has diuretic, anticancer, antipyretic, antioxidant, anthelmintic, analgesic and tonic activities [2]. In temperate and cold regions of Iran, winter cold is one of the most important environmental stresses which affect growth, development and yield of plants. So determination and improvement of freeze tolerance of winter plants such as Flixweed might promote their cultivation and utilization in cold regions. At present measuring the survival after a recovery period which is followed by a freezing test in controlled conditions is a common method for determining the level of plants freeze tolerance. Calculation of LT50 point or critical temperature based on survival percentage of plant is considered as a quantitative and simple method for evaluating the cold tolerance [1]. But sometimes this criterion is not enough alone and other indices (for example dry weight and Reduced dry matter temperature 50% of plants (RDMT50)) are used to achieve a more accurate estimation of cold tolerance level [3]. In spite of numerous medicinal and industrial properties of Flixweed, there is not a lot of information about freeze tolerance of this plant, so the objective of this study was evaluating the freeze tolerance of Flixweed by survival % and some of growth traits after recovery period.
Materials and methods
In order to evaluate freeze tolerance in some of Flixweed, a factorial experiment was conducted based on completely randomized design with three replications in faculty of agriculture, Ferdowsi University of Mashhad in autumn of 2009. Experimental factors include five ecotypes of Flixweed (Eghlid, Sabzewar, Hamedan, Torbat-e-Jam and Neyshabour) and 10 freezing temperature levels (from zero to -18 with 2 °C intervals). For this aim, Flixweed seeds were cultivated in pot in autumn and they were grown in natural weather until 5-7 leaf stage. Afterward for applying freezing temperatures, plants were transferred to a thermo gradient freezer. The initial temperature of programmable freezer was 5°C; but gradually decreased in a rate of 2°C.h-1 until reached to desired temperatures. When the freezer temperature reached to -2°C, the plants were treated by the Ice Nucleation Active Bacteria (INAB) to help the formation of ice nuclei in them, also to prevent from super-cooling of samples and to ensure that the mechanism of freeze resistance is tolerance not avoidance. After artificial freezing stress applying (which lasted up to two hours for each freezing temperature); Flixweed seedlings were transferred to greenhouse for recovery. Three weeks after freezing stress, survival percentage (SU %), Lethal temperature for 50% of plants according to the survival% (LT50su), number of leaf and reduced number of leaf temperature 50% (RNLT50), number of node and reduced number of node temperature 50% (RNNT50), dry weight and reduced dry matter temperature 50% (RDMT50) were evaluated. Analysis of variance was performed by MSTAT-C software and correlations between data were carried out by MINITAB 16 program. Mean separation was conducted by least significant difference (LSD) test at 1% probability level.
Results and Discussion
Results showed that Hamedan ecotype had the highest SU% and Neyshabour ecotype had the lowest SU%. In Eghlid and Neyshabour ecotypes, decline of SU% begun from higher temperarures (-8 °C) compared with other ecotypes (-10 °C). This trend was seen for dry weight and number of leaf too. At -12 °C, number of node in Hamedan ecotype decreased 30% approximately than control, while in Eghlid and Neyshabour ecotypes, this reduction was much higher. In this experiment LT50su ranged between -10.2 to -12.1 °C depending on the ecotypes. Ranking of Flixweed ecotypes according to the LT50su, RNLT50, RNNT50 and RDMT50 indices showed that the Neyshabour and Hamedan ecotypes were the most sensitive and tolerant Flixweed ecotypes to freezing stress respectively. In this survey, there was high and positive correlation between survival percentage and dry weight (r=0.69***), in addition there was negative and significant relationship between SU%, LT50su and RNNT50 (r=-0.67*** and r=-0.82*** respectively).
Conclusion
According to these results, it seems that temperature threshold for winter injury happening in Flixweed is -12 °C. Despite this for better understanding of cold tolerance of Flixweed, further researches are required under controlled and field conditions.
