The use of in vitro callus cultures as experimental model systems allows us to get closer to understanding the patterns and features of morphogenesis in intact plants. In this regard, the problem of realizing the morphogenetic potential of callus cells due to their pluri- and totipotency properties is of great interest. To solve this problem, it is important to use the histological approach, which involves studying the structures of developing tissues, organs and organisms in their interactions and relationships. This review article analyzes data devoted to the study of the histological features of formed primary morphogenic calli (formation of morphogenetic centers and superficial meristematic zones), as well as the in vitro morphogenesis pathways in calli that lead to the formation of regenerants (de novo organogenesis and in vitro somatic embryogenesis). The terminology used is considered. Some questions for discussion are raised. The opinion is expressed that histological (structural) studies should be considered as a methodologic basis for further investigation of various morphogenetic scenarios in in vitro callus cultures, especially in economically valuable plants and for biotechnological purposes.

Data on morphogenesis and some physiological and biochemical parameters of explants of five cultivars of Lavandula angustifoliaMill. under long-term micropropagation in vitro during nine...

The influence of the nutrient medium hormonal composition on the induction of calluso- and morphogenesis in Lavandula angustifolia Mill., as well as the content of some endogenous hormones (indolylacetic acid, cytokinins, abscisic acid) in morphogenic and non-morphogenic calli, were studied. The leaf explants were isolated from obtained in vitro plants of the Stepnaya and Vdala cultivars. In primary calli with a frequency of 5.7-11.6%, buds and shoots were formed on different Murashige and Skoog (MS) culture media supplemented with 6-benzylaminopurine, thidiazuron, kinetin, and gibberellic acid. In the callus of the first passage in both cultivars, the induction of morphogenesis was observed with the greatest frequency (39.5-43.2%) on the MS medium with the addition of 1.0 mg/l 6-benzylaminopurine and 1.0 mg/l kinetin. Morphogenic calli of the Vdala cultivar were characterized by a higher content of cytokinins, but a lower content of indolylacetic and abscisic acids compared with non-morphogenic ones.

Viral diseases affecting the essential oil rose, which is a valuable object of agricultural production, may have a significant negative impact on the economic value of this crop. Hence, the study and control of potentially dangerous viruses is essential to improving the quality of cultivars of this raw plant material, to enable production of valuable derivatives. The diversity of viruses affecting Rosa L. plants manifests itself in their conditional division into those that are specific to this crop, and those that are hosted by other plants. Representatives of both groups are found in different countries, however, a low number of viruses identified have been thoroughly studied through the use of experimental methods. In particular, with regard to many viruses, the issue of their spread remains open. The viruses infecting Rosa L. plants along with other crops are described in the literature in detail, as the range of hosts they affect is rather wide and well-studied. It is also possible to single out the three most significant viruses affecting this host—Prunus necrotic ringspot virus, Apple mosaic virus and Arabis mosaic virus which individually, or collectively, cause viral diseases that manifest themselves in mosaic symptoms. The most likely mechanisms for the spread of the Rosa L. species viruses are vegetative propagation procedures and transmission by various pests. These presumptions underlie viral infection control methods, including a well-thought-out planting scheme and provision of accurate plant care, which considers plant disinfection, disease monitoring associated with diagnostics and obtaining virus-free material through biotechnology techniques.

Mint represents a valuable medicinal and essential oil plant widely used in pharmacology, perfumery, cosmetics, and food industry. In order to maintain collections of cultivars and valuable samples, as well as to carry out breeding, the application of biotechnology appears to be promising for in vitro preservation of plant objects under the conditions of slow growth at low positive temperatures. The present study is focused on the morphometric parameters and genetic stability of the explants of two mint cultivars during their in vitro preservation at 4–6 ºС for a year without illumination. Meristems with two leaf primordia were cultivated on a nutrient medium in a culture room at 26 ºС and illumination of 2–3 klx with a 16-hour photoperiod. Microshoots developing from meristems were divided into single-node stem segments to be used as explants for deposition. After a year of deposition at 4–6 ºС without illumination, the number of viable explants in the Azhurnaya and Bergamotnaya cultivars was established to be 56.5 and 85.7%, respectively. The explants under study were characterized by the development of up to 2.5 shoots up to 13.2 mm long and rhizogenesis with a frequency of up to 52.3%. Following the deposition, microshoots were cut and transferred to a culture room to resume growth. After two subcultivations, viability (100%), morphometric parameters of microshoots, and multiplication index (up to 5.5–7.3) were fully restored. The ISSR-analysis performed according to four studied DNA markers revealed the microshoots of these cultivars to be completely identical to the original plants after in vitro preservation. The conducted studies proved the effectiveness of the conditions used for in vitro preservation of mint explants and confirmed the explant genetic stability after a year of deposition at 4–6 ºС.