ارزﻳﺎﺑﻲ ﺗﺤﻤﻞ ﺑﻪ ﻳﺦ زدﮔﻲ ﻧﻌﻨﺎع ﻓﻠﻔﻠﻲ (.Mentha piperita L) ﺗﺤﺖ ﺷﺮاﻳﻂ ﻛﻨﺘﺮل ﺷﺪه

Peppermint is a perennial and warm season plant, so winters cold is a threat for its survival. In order to evaluate freeze tolerance in peppermint a factorial experiment based on complete randomized design with 3 replications was carried out in college of agriculture, Ferdowsi University of Mashhad during 2010-11. For this aim samples from stolons and rhizomes of peppermint harvested monthly (from December 2010 to April 2011) from field and were placed in a thermo gradient freezer for freezing temperature (from 0 to -20 with 4°C intervals) apply. For assessing ability of organs to regrowth, freeze stressed stolon and rhizomes samples were cultivated in pots, and then pots were transferred to greenhouse. After 40 days, survival % and afterward
lethal temperature at which 50% of stolons and rhizomes died (LT50su) was calculated. Results showed that stolon survival % was 6.2% more than rhizome and its LT50su was 1°C less than rhizome. The most regrowth of stolon was observed in December at -4 °C and the maximum of survival% for rhizome was achieved in February at -4 °C. Stolon LT50su in different sampling times varied between -6.1 to -14.3°C and LT50su for rhizome ranged between -5.7 to -12.8 °C. According to LT50su indicator, peppermint had potential for freezing tolerance to -14°C during the cold months of year.