Origanum vulgare L. Cuttings Rhizogenesis in Microclonal Reproduction in Vitro

Abstract

Background. Oregano ( Origanum vulgare L.) is a valuable essential oil culture used in the pharmaceutical and food branches of industry as a source of biologically active substances. The optimization of microclonal propagation technology in vitro of this culture is considered topical for the development of the selection of oregano with a high content of essential oil and rapid multiplication of high-performance samples. Objective. This article aims to study the conditions of cuttings' rooting of oregano samples, valuable in terms of breeding, obtained at the last stage of in vitro cutting. Methods. Cuttings of eleven oregano genotypes obtained after the fourth cutting of the original maternal shoots were used as a material for the study of rhizogenesis in vitro . Roots formation and development of newly formed shoots were investigated by alteration of the carbohydrate and growth regulators composition in nutrient media for rhizogenesis. ½MS medium without growth regulators was used as a control medium. Experimental in growth regulator composition were MS-based media supplemented with one of the following components: indolylacetic acid (IAA) (2 mg/l), IAA (0.5 mg/l), indolylbutyric acid (IBA) (1 mg/l), IBA (0.5 mg/l), 0.5 mg/l IAA + 0.5 mg/l IBA. Sucrose (20 g/l) or glucose (20 g/l) was used as a carbon source. The influence of the composition of rhizogenesis media was estimated on the length of cuttings' root system, the length of newly formed shoots and the survival of regenerated plants after transfer to soil. Results. Formation of the oregano root system and newly formed shoots at a frequency of 100% occurred for all the studied genotypes and versions of media while the survival of regenerated plants in soil as a whole in the experiment for use of sucrose as a source of carbon was 63.82 ± 11.83% and for glucose 66.45 ± 11.62%. However, depending on the genotype and composition of the nutrient media, there was a variation in root system length, length of newly formed shoots and in the survival of regenerated plants in soil. A comparison of the results of rooting with sucrose or glucose in the medium for rhizogenesis did not reveal a significant difference between these compounds, but there was a tendency for better growth of the root system when using sucrose. A significant positive correlation was established between the cuttings' root system length and the survival of regenerated plants after transfer to soil (for sucrose r = 0.57, for glucose r = 0.51, r 0.05 = 0.24) and no correlation was proved between the newly formed shoots length and the survival of regenerated plants in soil (for sucrose r = –0.21, for glucose r = –0.03, r 0.05 = 0.24). Conclusions. It is proved that the influence of carbohydrate composition and type and concentration of growth regulators in the nutrient medium on the oregano cuttings' rhizogenesis obtained during the last cycle of microclonal propagation in vitro is genotype-specific. ½MS medium supplemented with 2 mg/l of indolylacetic acid, with sucrose (20 g/l) as a carbon source, proved to be most effective for root development in vitro and cuttings' adaptation in the soil for most of the genotypes studied.