Evaluation of Freezing Tolerance in Fenugreek (Trigonella foenum-graceum L.)

Plants grow well only within a specific temperature range. Getting out of this range is regarded as a stress. Low temperature is regarded as one of the important abiotic stress among the main factors threatening the growth of plants in temperate regions that causes disorder in the growth, development and operation of the plant by affecting some of vital processes of the plant. Environmental stresses especially cold stress affects the morphological and physiological features of the plant. Among these effects are damage to the cell membrane and change in its properties, reduction in photosynthesis and carbon dioxide efficiency, change in chlorophyll fluorescence characteristics, synthesis of chlorophyll and reducing the relative amount of water content. Since rapid and effective assessment of plant cold tolerance is important for researchers and also field trials have no regular process and have high error, different kinds of artificial freeze tests such as survival percentage test and regrowth after using stress has been developed.
In order to investigate the cold tolerance of Fenugreek, an investigation was done in factorial arrangement and in a completely random design in three replications in 2013-2014, in College of Agriculture in Ferdowsi University of Mashhad. The investigated factors include sowing date in four levels ( September 13, October 14, March 5, and April 3), ecotype in 10 levels (Azari, Ardestan, Tall, Dwarf, Shiraz, Shirvan, Mashhad, Neishabur, Hamedan and Hendi) and freezing temperature in seven levels ( control, 0, -3, -6, -9, -12, -15 °C). The plants grew in pots and cold acclimation in outside conditions then the plants which were planted in September and October as well as March and April. The pots were transferred to the freezer thermo gradient to apply the cold temperature in the middle of January and in the middle of May, respectively. Four weeks after applying the stress, survival percentage, Lethal Temperature 50% of Plant according to the Survival Percentage (LT50su), height, leaf area, Reduced Leaf Area Temperature (RLAT50), dry weight and Reduced Dry Matter Temperature 50 (RDMT50) were measured.
All ecotypes (except for Azari and Ardestan ecotypes) in the third sowing date could tolerate lowering temperature to -9 °C in every four sowing date. Lowering temperature to -12 °C also led to the death of all ecotypes in March and April sowing dates, while in September sowing date despite the death of most Fenugreek ecotypes, both Neyshabur and Mashhad ecotypes could tolerate this temperature. Also, in October 14 sowing date, in Neyshabur, Mashhad and Shirvan ecotypes the survival percentage was high, but the survival percentage of Azari, Ardestan and Tall compared with the control treatment decreased 61, 50 and 39, respectively, and the other ecotypes were destroyed completely. Ecotypes of Mashhad and Neyshabur had the lowest LT50su in the first and second sowing dates but in the third and fourth sowing date no significant differences was seen in this respect. In March 5 sowing date, after lowering temperature to -9 °C, the maximum percentage of decrease in height compared with control was in Dwarf ecotype (71 percent) and the minimum was seen in Shiraz (33 percent). In spite of this, Dwarf ecotype in the other sowing dates assigned to itself the lowest decrease percentage of height (respectively 35, 24 and 33 percent) and had a better ability to recovery. In every four sowing date lowering the temperature to -12 °C caused the total mortality of Hamedan, Hendi and Shiraz and they didnt have any leaf surface, but the response of the other ecotypes in October 14 sowing date was different. Two ecotypes Tall and Neyshabur having the highest (92 percent) and the lowest (66 percent) decrease in leaf surface compared with the control temperature were known as the most sensitive and the most tolerant ecotypes in this sowing date. In October 14 sowing date the response of the ecotypes to -6 °C compared with the other sowing date was better and the highest dry weight was associated with this date by lowering the temperature to -9 °C two ecotypes of Shirvan and Azari had the highest and the lowest decrease in dry weight (respectively 33 and 14 percent) in the second sowing date.
Lowering the temperature to less than -9 °C causes a decrease in the plant survival percentage and recovering in most of the ecotypes of Fenugreek. In spite of this, percentage of the plant survival depending on the sowing date, so that in the second sowing date the percentage of survival was more than the other sowing dates and except for Shiraz, Hamedan and Hendi ecotypes, the other ecotypes were able to tolerate -12 °C. Ecotypes of Shirvan, Mashhad, Neyshabur and Dwarf under both of spring and fall sowing dates had a better regrowth than the other ecotypes, while Azari and Ardestan ecotypes under the fall sowing showed a better regrowth than spring sowing date. There was a significant correlation between RLAT50 and RDMT50 with LT50su (r =0.53** and r = 0.64**, respectively), probably this subject shows the efficiency and the possibility of replacing each of these indexes in the investigation of the cold tolerance in Fenugreek. To sum up, the ecotypes of Mashhad, Neyshabur, Shirvan and Dwarf showed a better tolerance to freezing than the other ecotypes.