Effect of plant growth regulators BAP and IAA on micropropagation of Iranian lemon balm (Melissa officinalis L.) landraces

Lemon balm (Melissa officinalis L.) is a medicinal plant with a long history in traditional medicine that contains an essential oil. To evaluate the effect of genotype and plant growth regulators on morphologic response of lemon balm (Melissa officinalis L.) plant, nine lemon balm genotypes originating from different sources in Iran and two genotypes from Germany and Japan were used as plant material in present study. Nodal segments of lemon balm plants were cultured on MS medium supplemented with BAP (2 mg l(-1)), IAA (2 mg l(-1)) and IAA + BAP (2 mg l(-1)) on micropropagation. The results showed that use of 150 ppm nano-silver for 15 min to sterilize the explants proved to be effective. Addition of 2 mg l(-1) BAP to the MS medium in most of the genotypes resulted in a significant increase of the number of shoots per explants followed by MS + BAP + IAA. Maximum average shoot number (4.975+/-0.201 SE) was observed in Iranian landrace Hamadan2. The medium MS + 2 mg l(-1) IAA in most of the genotypes produced the longest shoots, the highest number of nodes per explant, and the Iranian landrace Fars in the medium MS+2 mg l(-1) IAA, produced the longest shoot (15.98+/-0.984 SE) and the highest number (9.6+/-0.451 SE) of nodes per explant among genotypes. The amount of callus was higher with IAA and IAA + BAP in comparison to MS and BAP. Among genotypes, the Iranian landraces Karaj and Qazvin2 in both Subculture 1 and 2, produced the highest callus amount. Micropropagated plants transferred to the greenhouse showed normal morphology and 90-100% survival during transplantation.