Chemical polymorphism is characteristic of essential oil bearing medicinal and aromatic large thyme (Thymus pulegioides). α-Terpinyl acetate chemotype is one of six T.pulegioides chemotypes found in Lithuania; α-terpinyl acetate is the main chemical compound of essential oil accumulated in this chemotype [1;2]. This chemotype of T. pulegiodes is very rare in Europe; mean while it has not been investigated in Lithuania fully. α-Terpinyl acetate is oxygenated monoterpene. Monoterpenes are strong allelochemicals therefore can affect associated plants (i. e. to inhibit or stimulate their seeds germination and/or seedlings growth) and composition of plant communities [3;4]. The aim of study was:1) to establish prevalence of T. pulegioides α-terpinyl acetate chemotype in Lithuania; 2) to determine allelopathic and autoalelopathic potential of essential oil of this chemotype.
131 different habitats of T. pulegioides were investigated to evaluate the distribution of T. pulegioides α-terpinyl acetate chemotype in Lithuania. The essential oils of T. pulegioides were isolated by hydrodistillation in the Clevenger-type apparatus and analysed by GC/FID and GC/MS methods. Allopathic effects (through air and water) of essential oil of T. pulegioides α-terpinyl acetate chemotype on germination and radicles growth of Trifolium pratense, Poa pratensis, Phleum pratense, Hypericum perforatum and T. pulegioides were investigated in laboratory conditions.
Results showed that T. pulegioides α-terpinyl acetate chemotype is rare in Lithuania: α-terpinyl acetate was found only in 35% of all investigated habitats. Amount of α-terpinyl acetate in essential oil was higher than 10% in four investigated habitats only. The essential oil of α-terpinyl acetate chemotype differently affected on seeds germination and radicles growth of investigated species. The essential oil of this chemotype strongly inhibited seeds germination and radicles growth of P. pratensis; the effect through water was stronger than trough air. The inhibitory effect of α-terpinyl acetate on germination of monocotyledon P.pratense was weaker. The negative effect of α-terpinyl acetate chemotype on seeds germination of T. pratense was the lowest. The effect of the essential oil of α-terpinyl acetate chemotype on radicles growth of H.perforatum was stronger than on seeds germination of this species. Autoalelopathic effect of essential oil of T. pulegioides α-terpinyl acetate chemotype was low.