Effect of Salt and Drought Stresses and Pretreatment of Salicylic acid on Seed Germination Characteristics of Lavender (Lavandula stricta Del.)

Recently, medicinal and aromatic plants have received much attention in several fields such as agro alimentary, perfumes, pharmaceutical industries and natural cosmetic products. Although secondary metabolites in the medicinal and aromatic plants impressed conventionally by their genotypes, their biosynthesis is strongly influenced by environmental factors. It means biotic and abiotic environmental factors affect growth parameters, essential oil yield and constituents. Abiotic environmental stresses especially salinity and drought has the most effect on medicinal plants. The genus Lavandula (lavender) of Lamiaceae family consists of about 30 species, many of which are found in Mediterranean, Sahara-Arabian and Iran-Turanian regions. There are only two species of Lavandula growing naturally in Iran, L. stricta Del. and L. sublepidata Rech. K. These species are not mentioned as medicinal plants in references; however L. soechas L., L. vera DC., L. angustifolia Mill. and L. dantata L. occurs naturally in Iran. Lavandula stricta Del. is a native aromatic plant in Iran from Lamiaceae. In traditional medicine, it is used for treatment of rheumatic pain, stomach pain and cough. Germination is one of the critical stages in the cycle of plants growth due to its important role in determining the final density of plant. Under water stress and salinity conditions, plant germination and its final density is important. Salicylic acid (from Latin salix) is a monohydroxybenzoic acid which is a type of phenolic acid and a beta hydroxy acid with C7H6O3 chemical formula. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone which is derived from salicin metabolism. Salicylic acid (SA) is a phenolic phytohormone and is found in plants with roles in plant growth and development, photosynthesis, transpiration, ion uptake and transport. SA also induces specific changes in leaf anatomy and chloroplast structure.
SA is involved in endogenous signaling, mediating in plant defense against pathogens. The signal can also move to nearby plants by salicylic acid being converted to the volatile ester, methyl salicylate. Salicylic acid has an important role in resistance to environmental stresses. In the current study, the effects of pretreatment of salicylic acid to eliminate salinity and drought stresses were evaluated on Lavender seed germination (Lavandula stricta Del.).
Seed samples of raised lavender were collected from Geno (Bandar Abbas) on May 2013. Two experiments were conducted based on completely randomized design with three levels of Salicylic acid (0, 0.1 and 0.5 mM) and four levels (0, -2, -4 and -6 bar) of drought and salinity stresses with three replications in Horticultural Sciences department, Plant production faculty of Gorgan University of Agricultural Sciences and Natural Resources (GUASNR). Plumule and radicle length, germination percentage and seed vigor were evaluated.
Results Results indicated that plumule and radicle length, germination percentage and seed vigor were significantly decreased by increasing drought and salinity stresses. The absence of pretreatment with salicylic acid were lead to increase negative effects of salinity in comparison with non-pretreated in the studied trait. However salinity stress levels -2 and -6 bar and pretreatments increased all traits significantly. Overall, the results showed that among total characteristics, plumule length is more sensitive in to drought and salinity stresses. As a result, the best range of moisture for lavender seeds germination is from non-stress conditions to -2 bars. It seems that seed germination on lavender has more tolerance to drought stress conditions than salinity stress conditions. Since the climate change will result in ecological degradation and further threaten the fragility of dry and saline lands, with serious consequences for crop and livestock production and food security. Today, an estimated one billion people face hunger and absolute poverty, and in many developing countries, the gap between food production and demand is increasing rapidly. The diversity contained within plant genetic resources provides the variability needed for adaptation, and therefore will serve as a key element in maintaining food and medicine production under novel temperature, precipitation, and pest and disease conditions. Key to successful crop improvement is a continued supply of genetic diversity, including new or improved variability for target traits such as early flowering as an escape mechanism to drought and salinity. Given that Lavandula stricta Del.is native to Iran, it seems that this plant is a good candidate for further research in this area.