The effect of freezing stress on electrolyte leakage in Trigonella foenum-graecum ecotypes

Introduction In tolerance to coldness researches, scholars are looking for exams which in addition to having easiness, velocity and enough validity, be repetitive as well and mean while the feasibility of controlling the thermal conditions be in it. Using different kinds of freezing exams in controlled and artificial conditions have been suggested. Hence, damage evaluation via measuring the electrolyte leakage and determining the Lethal Temperature 50 According to the Electrolyte Leakage percentage (LT50el) is considered as a suitable and direct method for evaluating the amount of coldness damages by the researchers. Materials and method In order to evaluate freezing tolerance of fenugreek a factorial experiment in 2013-2014 year based on completely randomized design with three replications was conducted under controlled conditions in faculty of agriculture, 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, Long foot, Short foot, Shiraz, Shirvan, Mashhad, Neyshabur, Hamedan and Hendi) and freezing temperature in seven levels (control, 0, -3, -6, -9, -12, -15 0C). The potted plants grew and cold acclimation in outside conditions then the plants which were implanted in September and October, and the plants which were implanted in March and April , were transferred to the freezer thermo gradient to apply the cold temperature in the middle of December and in the middle of May respectively. After freezing, Percentage Electrolyte leakage (%EL) and Lethal Temperature 50 According to the Electrolyte Leakage percentage (LT50el) was determined. Survival percentage of them after freezing and 28 days growth was measured in the greenhouse. Results and Discussion Although in the all sowing dates the electrolyte leakage was constant up to the temperature of -6 0C and by more reduction in temperature, it had an increasing trend, but the leakage increase velocity in the sowing dates in the first decade of March war more than other dates. As in this sowing date by reducing the temperature from zero to -15 0C, the percentages of electrolyte leakage increased about 71 percent. In some ecotypes such as Shiraz and Hamedan by causing delay in sowing date from July to April the percentage of electrolyte leakage was increased. Although the electrolyte leakage percentage in all ecotypes in the second sowing date of fall and spring was reduced in compare to the first sowing date, the lowest and the highest reduction resulted from delay in sowing date belonged to Hamedan and Ardestan respectively. Although by temperature reduction the percentage of electrolyte leakage was increased in the all ecotypes, but this increase was more intense in the Hendi ecotype than other ones. In this ecotype by reducing the temperature from zero to -15 0C, the electrolyte leakage percentage increased 73 percent whereas in Neyshabur ecotype this increase was 53 percent. The percentage of electrolyte leakage from the Trigonella foenum-graecum ecotypes in each sowing date increased by temperature reduction. In the majority of ecotypes this increasing trend was witnessed from the -6 0C. In the all ecotypes, the October 14 sowing date in the majority of the studied temperatures had lower leakage percentage than other sowing date. According to the LT50el index, the sowing date of the first decade of October in ecotypes was lower in compare to other dates. In other words, earlier sowing date of ecotypes probably leads to increase in plants sensitivity to coldness. The highest and lowest tolerance to freezing, according to this index, belonged to Neyshabur and Azeri ecotypes respectively. Between Lethal Temperature 50 According to the Electrolyte Leakage percentage (LT50el) and survival (r=-0.536*) negative and significant correlation was witnessed which indicates that using this index in evaluating the damage of freezing tolerance in Trigonella foenum-graecum is possible. Conclusion Generally in this study in all of the ecotypes, reducing the temperature led to increase in the percentage of electrolyte leakage. This leakage increase slope in the majority of ecotypes began from -6 0C and in -15 0C was maximized. Delay in autumnal and spring sowing dates by affecting the plant growth stage cause increase in plants tolerance to freezing. In other words, the plants which were in advanced vegetative level in the exerting time of freezing temperatures had lower tolerance to freezing. Among the studied ecotypes, however, the Neyshabur and Azeri ecotypes had the highest and the lowest tolerance to freezing respectively considering the leakage amount and LT50el. Therefore, it seems that the sowing date of October is suitable for sowing Neyshabur, Mashhad, Shirvan and Short foot ecotypes which had lower leakage percentage and more suitable LT50el in compare with other ecotypes. However, more researches in evaluating the plant’s tolerance to freezing in real winter conditions and determining correlation relationships between the results in controlled situations and farm will be useful.