Lemon verbena (Lippia citriodora H.B.K.) from Verbenaceae is one of the most important aromatic plants which is cultivated mainly due to the lemon-like aroma from the leaves.1 It is indigenous to South America and is cultivated in northern Africa, southern Europe and north of Iran.2 It has been used in treating asthma, spasms, cold, fever, flatulence, colic, diarrhea, indigestion, insomnia and anxiety for many years.
The essential oil of the fragrant leaves with various levels and types of effective ingredients and constituents includes 24 different main components.6,7Argyropoulou, et al. (2007) reported that the most important components of essential oil from lemon verbena were geranial, neral and limonene during different Phenological Stages.3,4,1
The short period of growth, low need for cultivating operations and its medical properties has attracted attentions. Hence to obtain the best economical yield the proper climate conditions (temperature, humidity, light) is needed. The most favorable temperature for the cultivation and growth of lemon verbena ranges from 12 to 25 ”C. In some regions low temperature (LT) as one of the most important abiotic factors limits growth, productivity and geographical distribution of agricultural crops.8 Low temperature (LT) decreases the biosynthetic activity of plants and inhibits the normal function of their physiological processes and may cause permanent injuries, finally leading to death.9,10
According to the report of Brando and Durigan (2004), the cold temperature and frost had adverse influence on Lippia balansae Briq. in a way that there was no relative dominance (crown cover) just after frost and 14% of individuals were killed totally in frost susceptibility test.### Decrease of these environmental threats in line with increase of crops yield needs application of new agricultural techniques.
One of these techniques is application of polymers. Polymers have been used worldwide for the last few decades. They have so many applications in different fields such as agriculture.11,12 In this research the property of antichilling has been considered and investigated in polymers. Antichilling polymers such as Poly vinyl alcohol (PVA), Glycerol (GLY) and Ethylene glycol (EG) can play an important role in agricultural operations for creating a climate beneficial to plant growth. PVA is the largest volume synthetic water-soluble polymer produced in the world.13 PVA has excellent chemical resistance, a good mechanical property and an excellent biocompatibility.14 In addition, PVA is biodegradable in the presence of suitable microorganisms. The several useful properties of PVA make it particularly interesting to elaborate environmentally friendly materials.15-18 GLY is a nontoxic, edible, biodegradable sugar alcohol making it an ideal ”environmentally friendly” agricultural chemical. The influence of GLY as a cryoprotective agent used in cell and tissue cyrogenetic storage has been repeatedly demonstrated.19,20 EG is a group of organic chemicals used in antifreeze formulations, hydraulic fluids, surface coatings, surfactants and emulsifiers.21,22 It was found that Polymer of GLY could prevent freezing of leaves if foliar applied consisting of water, glycerol, a spreader, and alcohol. Furthermore, soaking of Castor bean (Ricinus communis L.) seeds in GLY improved the content of essential oil in stress conditions.20Considering the agricultural and pharmacological importance of medicinal plants as lemon verbena and the negative effects of environmental stresses such as low temperature on yield and production, it is necessary to improve the agricultural operations and technique to overcome the irreparable loss of products. There is no comprehensive research about the effect of low temperatures on lemon verbena EO quantity and quality and no study has conducted on polymers formulations as antichilling agents. Hence, this research was aimed to evaluate the foliar application effects of antichilling polymer formulations on phytochemical traits of lemon verbena (Lippia citriodora H.B.K.) under induction of different temperatures.