Research article EFFECT OF PRE-TREATMENT OF LEMON BALM (MELISSA OFFICINALIS L.) SEEDS ON SEED GERMINATION AND SEEDLINGS GROWTH UNDER SALT STRESS

High germination rate and vigorous early growth under salty soils is preferred because, seedlings establishment at early growth stages of crop plants is severely affected by soil salinity. A study germination and seedling growth of Lemon Balm (Melissa officinalis L.) was assessed using factorial experiment based on a completely randomized design with three replications. This experiment was carried out at the laboratory of Horticulture faculty of Gorgan Agricultural and Natural Resources University, Iran, March 2014. The seeds divided into five groups, equally. The first group was soaked for 6h in distilled water at 20C to serve as control while four other groups were soaked in 0.1, 0.5, 1 and 1.5 mM of salicylic acid respectively (Senaranta et al, 2002). Afterward, seeds air dried at room temperature for 36h. After a preliminary test for low water potential tolerance (caused by NaCl), four water potential levels were selected and used for germination trials. The drought solutions had water potential of zero (control), −2, −4 and −6 Bar. The results showed that effect of salt stress on germination percentage, germination rate, radical length and weight and hypocotyls length and weight were significant. Effect of Salicylic acid (SA) and interaction between salt stress and SA on germination rate were significant only. Germination percentage and germination rate was significantly increased by SA under salinity conditions compared to non treatment of SA. Priming with 1.5 mM SA showed maximum radicle and hypocotyl length. Priming with SA could improve radical length and radical dry weight in all salinity levels. However, treated seeds with SA produced the higher hypocotyl length in all salinity levels than untreated seeds. SA decreased radicle length, while increased hypocotyl length relatively Dry weight of hypocotyl was decreased due to salinity stress but seedlings raised from seeds primed with SA improved dry weight of seedlings as compared to non treatment of SA. All traits responded negatively with lowering water potential but using salicylic acid ameliorated the harmful effect of induced stress on measured traits. The concentration of 1.5 mM of salicylic acid on measured traits was more effective compared with the other levels. Therefore, seed pre-treatment with salicylic acid could be a suitable tool for improving germination characteristics of Lemon Balm under low water potential.