Promising essential oil plants from the Lamiaceae family, the raw materials of which are a source of valuable essential oil for pharmaceutical, perfume, cosmetic and food industries, pertain to the Monarda L genus. The Monarda didyma L. and Monarda fistulosa L. species were first imported to Ukraine from Europe and America in the middle of the twentieth century, and today they are successfully cultivated as decorative, spicy-aromatic and medicinal plants. The purpose of this study was to determine the morphobiological features, valuable economic and selective traits of Monarda didyma, Monarda fistulosa and Monarda × hybrida hort., developed for the arid conditions of the southern steppe of Ukraine at the Institute of Rice of the NAAS. The experimental part of the study was performed in 2016-2018 on southern sandy and medium loam black soils (chernozem) in the state enterprise (SE) "Research farm "Novokakhovske". The experiment was conducted using field, laboratory, mathematical and statistical methods in accordance with the generally accepted methods and guidelines in Ukraine. The plants of developed varieties undergo a full cycle of development under arid conditions of the southern steppe of Ukraine and are characterised by an increased decorativeness, goodeconomic value, high drought and winter tolerance as well as the resistance to pest damage. Yield, mass fraction and content of essential oil in the aboveground mass of plants were determined. Maximal plant height (120 cm), yield of aboveground mass (18 t/ha), concentration of essential oil (0.8% of crude mass) and thymol content (78.3%) are typical of the variety of Monarda fistulosa, Premiera. The variety of Monarda fistulosa, Fortuna, and variety of Monarda × hybrida hort., Tonya, were inferior to Premiera in all of the above-mentioned indicators but demonstrated increased decorativeness and greater resistance to the fungi causing powdery mildew (Erysiphe monardae, Golovinomyces biocellatus). Therefore, they can be recommended for region-wide cultivation in the agricultural enterprises of the southern steppe of Ukraine as promising essential oil, spice-aromatic and decorative crops. The yield of essential oil from raw materials of Monarda didyma variety, Nizhnist, was lower by 32.9% and 26.8%, while its concentration was lower by 37.5% and 28.6%, compared to the Monarda fistulosa varieties Premiera and Fortuna, respectively.

Plant forms were selected from seed generation of Thymus serpillum L. and Thymus pulegioides L. introduced in Kherson region. These forms differ by morphobiological grounds and the content and composition of essential oil. In the process of chemical research we selected forms of T. serpillum and T. pulegioides and found that the maximum mass fraction of essential oil was found in the form of T. Serpillum-No.17-07 and amounted to 0.29% of freshly weight or 1.1% by weight air-dry material. In plants form T. serpillum18-07, those indicator was slightly lower — 0.18 and 0.67% respectively. Composition component of essential oil was studied. The dominant components of the essential oil of two forms of Thymus serpillum is thymol and γ-terpynen. Mass fraction of thymol in oil in the form No.17-07 is 40.70%, in the form No.18-07 — 40.29%. Mass fraction γ-terpynenu — 12.88% and 23.31% respectively. The main components of the essential oil of Thymus pulegioides L. form No.2/6-07 are neral and heranial (amounting to 50.25%).

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