In Vitro Polyploidization of Thymus vulgaris L. and Its Effect on Composition of Essential Oils

Abstract

The aim of this work was to find an effective protocol for in vitro propagation and to perform the in vitro polyploidization of diploid Thymus vulgaris (2n = 30) using two experimental methods based on the use of oryzalin, an antimitotic agent. The ploidy level of the obtained shoots was checked by flow cytometric analysis. The most efficient conditions for inducing polyploidy were oryzalin concentrations of 0.346 and 1.73 mg L−1 present in the medium for two weeks. The vital polyploid shoots were multiplied for further evaluation, rooting and final transfer to nonsterile glasshouse and field conditions. The chemical compositions of the essential oils (EOs)—which were obtained from dried field grown plants by steam distillation—were analyzed by gas chromatography/mass spectrometry (GC/MS). The identified substances contributed approximately 95% to the total peak area. Statistical analysis revealed that the tetraploid subclone and the diploid reference plant do not differ in total terpene content, but they do differ in the relative proportions of all the individual terpenes with the exception of α-pinene and UN5, indicating that both clones produce EOs of different quality. The obtained results showed the possibility of developing more efficient botanical insecticides based on EOs obtained from the tetraploid plants.

Polyploidy in Industrial Crops: Applications and Perspectives in Plant Breeding

“…As reported by Trojak-Goluch and Skomra [73] as well as Švécarová et al [78], hop tetraploids showed poorer acclimatisation to field conditions and poorer rooting. Similar traits were displayed by tetraploids of T. vulgaris [79] and C. sativa [74]. Contrasting results were obtained by Tang et al for tetraploids of P. tomentosa, whose seedlings were characterised by a strong root system and high acclimatisation ability (90%) [82].…”

“…It involves a 2-week culture of nodal fragments on MS medium with the addition of oryzalin. The number of polyploids obtained this way represented 10.3 to 66.7% of the regenerants [79]. The study by Švécarová et al showed that for H. lupulus, it is possible to obtain a greater number of polyploids (70% of all tested) using this method [78].…”

“…The treatment of plant material also exerts a positive influence, especially shoot tips with semi-solid antimitotic stock (1% agar) [70]. Under in vitro conditions, however, aqueous solutions of antimitotic agents are usually added to the liquid or agar-solidified growth media [79,80,83]. After a certain time of antimitotic action, the plant culture is transferred to a fresh medium in order to root or regenerate plants.…”

“…The leaves of polyploids tend to be broader, thicker, often intensely green, and covered with more hairs than in diploids. Thicker and dark green leaves are found in tetraploids of O. basilicum [89], T. vulgaris [79], N. alata [66]. Different leaf shapes and margins can be observed in polyploid Tetradenia riparia (Hochst) Codd, used in the pharmaceutical and perfume industry [95].…”

“…Many literature reports indicate that the size of polyploid plants is different from that recorded in diploids. In some species, polyploid forms are larger and stronger compared to diploid forms, e.g., in T. vulgaris [79], T. ammi [105], M. chamomilla [3], A. vera [106,109], Z. officinale [111]. In many other species, such as C. sativa [74,101], C. intybus [90], E. purpurea [104,115], polyploid plants are lower, or changes are hardly noticeable.…”