Measures to propagate essential oil roses implemented for example, by the Research Institute of Agriculture of Crimea include, among others, systemic precautions to prevent the spread of pests and diseases. The essential oil roses cultivation technology includes providing optimal conditions for their growth; implementing care measures at the right time; weed, insect and pest control, as well as the observance of quarantine regulations and preventive treatment of plants relocated from different sites of the nursery. In the selected area, the predecessor culture is harvested, and the stubble is broken as deep as 8–10 cm. Upon the emergence of weeds above ground repeated stubble breaking is carried out with the application of an herbicide (glyphosate), at a dose of 4–6 mL/ha⁻¹. In October, fertilizers such as ammophos at a dose of 200–400 kg/ha⁻¹ are applied, and if possible, organic fertilizers are used; finally, trench ploughing as deep as 40 cm is carried out. From March onwards, the field surface autumn fallow is to be maintained and the soil surface is to be cleared of weed seeds and vegetative rudiments; the area is cultivated three to five times. Prior to planting essential oil rose seedlings, the soil is harrowed as deep as 18 cm. Roses are planted in October-November (as well as during frost-free periods in winter) according to the scheme 3.0 × 0.85 m with a density of 4000 plants/ha⁻¹. For planting, selected conditioned plantlets previously dipped in a mash of clay and cow manure are used. The care for non-bearing plants (during the next year after planting) focuses, mainly, on intensive weed, disease and pest control. As weeds germinate, mechanical inter-row tillage is carried out as deep as 10–16 cm for 3–5 times. If weeds are dense inter-row weed pulling is carried out. In October–November, seedlings are underplanted manually, in the required quantity. In the second year after planting, in February–March, bushes are pruned along with the culling of bushes manifesting signs of infection and deformation and collecting samples for the diagnostic laboratory. Since the essential oil rose is used both for obtaining oil and producing jam, syrups and soaps, the care for plants during the harvesting period is limited to weeding, fertilizing and watering, without the use of chemical crop protection products that may affect the quality of the essential oil rose derivatives. The crop protection interventions involving the use of herbicides, fungicides or insecto-acaricides can be carried out only a month before or after the harvesting. Therefore, the identification of phytopathological damage and phytosanitary control, during the flowering period (from late May to early July) is limited to detecting and culling infected plants, along with intensive weeding. The strongest six or seven shoots are left on the plant, two of them located in the centre of the bush are cut 30–35 cm high from the soil surface, and the rest are cut 20–25 cm high from the soil surface. All the damaged and weak shoots are cut at the level of the soil surface. Plants manifesting obvious viral damage are discarded and burned. Agronomists inspect the plots on a weekly basis under the routine procedure for plant care, pruning and weeding. When finding suspicious spots and deformations, the location of the infected plant is noted; the disease manifestations in bushes are photographed and sent to the laboratory. The rose bushes manifesting clear signs of obvious disease symptoms are removed from the area to prevent disease spread. However, regular inspection and culling of low-quality material at all stages of plant cultivation does not rule out the presence and accumulation of a viral load. For this reason, planting material renewal is most effective if in vitro collection materials are used where valuable genotypes are preserved and multiplied by clonal micropropagation ^[1][2].

Figure 1 presents integrated data on traditional measures to control viral infections.

Virus-free planting material is produced through the use of biotechnological techniques: apical meristem culture methods including the use of thermotherapy or chemotherapy ^[3].

Apical meristem culture is based on the concept that the meristem is so structured that its upper layers (an apical meristem) give rise to cover tissues while its lower layers give rise to the conduction system. Due to the fact that these layers are compartmentalized the ability of a virus to penetrate the upper layers via the conduction system is limited. Viruses move along the vascular system at a higher speed; however, it is presumed that viral particles can slowly make their way into the upper layers via the plasmodesmata connecting the meristematic cells. Another reason for the absence of viruses in certain parts of the meristem is that cell division and virus multiplication and spread, occur at different rates. This is also the reason for the presence of certain viruses and strains in various parts of the meristem ^[4]. Clonal in vitro propagation is based on apical meristem culture. It is a cell engineering method whereby, within a short time, valuable cultivars are multiplied and introduced into production and virus-free planting material is produced. This method is also well-known for essential-oil roses ^[5][6][7].

Thermotherapy is based on inhibiting virus reproduction or preventing the viral particles’ penetration into the re-growing parts of a plant by means of a high temperature, whereby the integrity of cell compartments are not impaired, and the damage to plant cells and tissues is minimized. There are a few variations of this method: (1) Hot water dipping. This method is applied to the resting parts of a plant (tubers, buds, cuttings). These parts are dipped in hot water as they are able to survive higher temperatures than actively vegetating plants. Upon thermotherapy the plant fragments are dried a little in the air, preferably in aseptic conditions. (2) The dry-air process is preferable for vegetating parts of a plant, whereby, they are exposed to warm air at temperatures of 35–40 °C over several weeks. This method does not impair plant health and helps to produce virus-free shoot apexes, subsequently grafted on the rootstock or rooted ^[4][8].

Chemotherapy can be successful in combination with thermotherapy and apical meristem culture ^[4]. The best-known antiviral agent is ribavirin that inhibits replication of multiple animal and plant viruses ^[9]. The studies carried out by Yegorova ^[10] to look at the effect of virazole (ribavirin) identified features specific to the essential oil rose explants’ morphogenesis in vitro, subject to the agent’s concentrations in the culture medium. The chemotherapy conditions optimization, centres around the empirical identification of the virus-inhibiting agent’s concentration and exposure time, taking into account the explant type and the explant treatment method. It is critical to minimize the negative impact of the agent on the explant. For two months the meristems and apexes isolated from developing shoots were exposed to chemotherapy with virazole at concentrations of 20.0–25.0 mg/L. A decrease in the number of leaves, buds and developing explants, as well as the shoot length, by 1.2–2.7 times compared to the control group was observed. At the same time, on further micropropagation of viable shoots, the development of the plants grown with chemotherapy scarcely differed from the control group. This points to the possibility of using virazole during the stated period, and in the empirically identified concentration, for essential oil rose chemotherapy when carrying out sequential cultivation of the meristems and shoot apexes.

Mitrofanova et al. ^[4] described a model system for viral elimination in flower crops comprised of the following basic elements: screening the plants for viruses, thermo- or chemotherapy, apical meristem culture, the adapted plants retested for viruses. This model involves the following stages:

• Mother plant diagnosis using test plants, electron microscopy, ELISA and PCR techniques.
• In case the plant is infected, thermotherapy in vitro, or in vivo at 37 °C for 4–15 weeks, or chemotherapy with virucides in vitro.
• Plant tissue culture growth and plant regeneration on artificial nutrient media over 14–20 weeks.
• Regenerated plants adaptated in vitro at 15–20 °C over 3–4 weeks.
• The adapted plants retested using the test plants, ELISA and PCR techniques.
• Obtaining of virus-free plants and their certification.