In vitro rooting of some Thymus L. species

Abstract

Today, biotechnology methods are being intensively introduced into the breeding of many agricultural crops to obtain initial material with valuable traits, in particular clonal micropropagation, which allows rapidly propagating and improving valuable planting material. The purpose of the current study was to optimize the conditions for effective in vitro rooting for the development of a method for clonal micropropagation of 7 thyme species. The current paper has presented a comparative analysis of the cultivation of explants of Thymus x citriodorus (Pers.) Schreb., T. marschallianus Willd., T. tauricus Klokov et Des.-Shost., T. serpyllum L., T. vulgaris L., T. pseudonummularius Klok. et Schost., T. caucasicus Willd. on different variants of the Murashige and Skoog (MS) nutrient medium at the 2nd stage of micropropagation itself and at the 3rd stage of in vitro rooting. When analyzing the development of T. caucasicus, T. tauricus, and T. pseudonummularius explants at the 2nd stage on MS medium with 1.0 mg/l of kinetin and 20 g/l of sucrose, there have been established a high rooting rate (80.8–91.1%) and root number (3.8–6.6 pcs./shoot), indicating the possibility to exclude a special rooting stage in these three thyme species. At the 3rd stage, when cultivating explants (stem segments with a node) on media with different auxin concentrations (IAA, IMC, and NAA), there has been established that IMC exhibited greater rhizogenic capacity. The optimal medium for rooting of T. serpullum, T. x citriodorus, and T. vulgaris was ½ MS with 1.0 mg/l of IMC, on which there were obtained 89.5–98.6% of rooted microshoots without vitrification, having from 9.2 to 10.7 roots. For T. marschallianus, the ½ MS medium with 0.5 mg/l of NUK and 20 g/l of glucose provided the maximum rhizogenesis rate (84.8%) and the formation of normally developed microshoots.