Alleviation of low temperatures injury on lemon verbena (Lippia citriodora H.B.K.) by exogenous application of adjuvants in anti-chilling formulations

Background: Lemon verbena (Lippia citriodora H.B.K) from Verbenaceae is a sensitive plant to low temperatures as abiotic stress. Objective: The objective of this research was to evaluate the effects of adjuvants and anti-chilling formulations on lemon verbena (Lippia citriodora H.B.K) leaves under low temperatures. Methods: The combined analysis was done on the basis of a randomized complete blocks design (RCBD) with 28 treatments and 3 replications. The three factors included two anti-chilling formulations (glycerol, and glycerol + polyvinyl alcohol), seven adjuvants formulations (α-tocopherol, amino acids of proline + glycine-betaine, and ABA), and two levels of low temperature (5 and 10 °C). Results: The treatment of glycerol + proline + glycine-betaine + ABA reduced the damaging effects of low temperature in biomass, essential oil content, and osmoprotectants, while the highest protection by antioxidant pigments was obtained in glycerol + α-tocopherol + ABA. Enzymes activities and polyphenol content showed the best results by glycerol + ABA. Conclusion: The best formulations were glycerol + proline + glycine-betaine + ABA and glycerol + ABA from the viewpoint of economic yield and also qualitative protection against low temperature, respectively. The efficiency of the mentioned formulations was due to their direct protective function and the indirect influence of adjuvants in a synergistic interaction with other components of the formulation.