Clonal micropropagation of some species of the genus Thymus L.

Abstract

The aim of the work was to study the influence of cultivation factors on the explants development to optimize the protocol of in vitro clonal micropropagation of four species of the genus Thymus L., valuable essential oil and medicinal plants. Conditions that ensure the production of up to 94.2 % of sterile explants were selected. It has been established that, when introduced into in vitro culture, it is advisable to use shoot tips and stem segments with a node (isolated from donor plants) and cultivate them in foil-covered test tubes. The optimal culture media for the first stage of micropropagation were determined: Murashige and Skoog (MS) medium with 1.0 mg/l benzylaminopurine (BAP) for Thymus serpyllum L. or MS with 1.0 mg/l kinetin and 1.0 mg/l gibberellic acids (GA3) for T. vulgaris L. ‘Gornyy Balzam’, T. × citriodorus (Pers.) Schreb. ‘Doone Valley’, T. caucasicus Willd. ex Ronniger. At the second stage of clonal micropropagation, it is advisable to cultivate T. caucasicus and T. serpyllum explants during 40 days, but T. vulgaris and T. × citriodorus – during 60 days. The maximum multiplication index at the recommended cultivation duration was obtained for T. × citriodorus (9.9) on MS medium without hormones, T. caucasicus (16.1) and T. vulgaris (10.0) – on MS medium with 1.0 mg/l kinetin., and T. serpyllum (6.8) on MS medium with 1.0 mg/l BAP. When comparing different culture vessels (tubes, jars and flasks), the effectiveness of jars was revealed. This type of culture vessels made it possible to increase the multiplication index up to 2.1–5.7 times. It was revealed that when microshoots of four thyme species were cultivated on MS medium with 1.0 mg/l IBA, the rooting rate reached 84.6–98.9 %. The frequency of adaptation ex vitro when using a mixture of peat and perlite (1:1) ranged from 62.8 to 89.5 %.