Evaluation of Cold Tolerance in Field Grown Mentha (Mentha piperita‎ L.)‎ under ‎Laboratory Conditions by Electrolyte Leakage Test

In order to determine cold tolerance of field grown Mentha (Mentha Piperita L.) under controlled conditions, using electrolyte leakage index, an experiment was carried out at the College of Agriculture, Ferdowsi University of Mashhad, based on a completely randomized design with four replications. Experimental factors included six freezing temperatures (Zero, -4, -8, -12, -16 and -20 °C), seven harvest ‎time (November, December, January, February, March, April and May) and ‎four Peppermint organs (leaves, Stems, Stolons and Rhizomes). So, field grown ‎and acclimated Pepermint was harvested from the faculty field every month. ‎After separating the Peppermint organs, they were subjected to freezing ‎temperatures. The membrane stability index was measured through ‎electrolyte leakage (EL) and also lethal temperature 50 ‎according to EL (LT50el) was determined. The results showed that electrolyte leakages were affected significantly by freezing temperature. By reduction of freezing temperature electrolyte leakages percentage increased. Among different organs of peppermint, stolon and leaf were the most cold tolerant and the most cold sensitive according to EL and LT50el, respectively. Also cold tolerance varied according to different harvest time in all organs. However, in May, all organs had lowest cold tolerance. Also leaves and stolons had the highest and the lowest LT50el, respectively. For all organs the highest LT50el‎ was observed in May. According to the high correlation between electrolyte leakages percent and LT50el (r = 0.96**), it seems that using this index for evaluation of freezing tolerance injury in Mentha piperita could be useful.