Effect of Explant Type and Different Hormonal Combinations on Direct Regeneration of Lemon balm (Melissa officinalis L.)

Lemon balm (Melissa officinalis L.) is an herbaceous perennial plant of the Lamiaceae family that has a wide edible and medicinal uses. In this research the potential of five different explants (nodal segments، shoot tip، cotyledon، hypocotyl and leaf segments) on MS mediums supplemented with different concentrations of 6-Benzylaminopurine (BAP) (2. 2، 4. 4 and 8. 8 µm) alone or in combination with 1µm Indoleacetic acid (IAA) for direct regeneration of Lemon balm was investigated. The experiment was conducted using a factorial based on completely randomized design with three replications. The maximum mean number of shoots (23. 59 and 16. 90 shoots in shoot tip and nodal segment explants، respectively) was observed on the MS medium with 8. 8 µm BAP. The highest regeneration rate (99%) in shoot tip and nodal segment explants was achieved on the MS medium supplemented with 8. 8 and 2. 2 µm BAP، respectively. No shoot regeneration occurred in other explants. The rooting of regenerated shoots was assessed on MS، ½MS and MS medium supplemented with 1، 2. 5، 4. 92 and 9. 84 µm Indole butyric acid (IBA). The highest mean number of roots (9. 06 roots per explants) was observed on the MS medium supplemented with 4. 92 µm IBA.