Micropropagation of centennial tertiary relict trees of Liquidambar orientalis Miller through meristematic nodules produced by cultures of primordial shoots

Key message This paper provides an important micropropagation method that might be used for conservation and commercial production of tertiary relict tree Liquidambar orientalis . The Liquidambar orientalis Miller is an important tree as a tertiary relict endemic species in terms of plant biodiversity, and has economic value due to the balsam it produces. In the present study, an efficient micropropagation method was developed for the L. orientalis. Initially, primordial shoot explants isolated from axillary buds were cultured on Murashige and Skoog and Woody Plant Medium (WPM) containing different plant growth regulators (PGRs). The highest number of shoots per explant was obtained on WPM supplemented with 1.0 mg/L 6-benzylaminopurine (BAP) and 1.0 mg/L indole-3-butyric acid (IBA) (shoot proliferation medium: SPM). These shoots were then subcultured continuously on SPM for a period of 18 months. Meristematic nodule clusters were formed at the base of the cultured shoots in SPM, where multiple shoots developed from them. The number of shoots per explant was increased approximately 2.8-fold by applying various strategies such as different explant type (single shoots and shoot clusters) and culture vessels (Glass Tube, 210-cc Glass culture jar, 400-cc Glass culture jar, and Vitro Vent ® ). Shoot clusters cultured in ventilated Vitro Vent ® vessels on SPM gave best result for shoot propagation. In vitro shoots rooted best on WPM containing 30 g/L sucrose, 120 mg/L ethylenediamine di-2-hydroxyphenyl acetate ferric (Fe-EDDHA) and 4.0 mg/L IBA. All plantlets were successfully acclimatized in a glasshouse and then plants were transferred to the field. This methodology has been adapted by a commercial producer.