A magnetic pulse treatment led to an increase in the Raspberry bushy dwarf Idaeovirus-free microplants’ output and their phenolic composition change. The greatest output of the virus-free raspberries microplants (80–82%) was marked after complex treatment with pulsed and rotating magnetic fields with a time-changing frequency from 3.2 to 51 Hz, as well as with a pulsed magnetic field with a frequency from 1 to 10 Hz. The pulsed and rotating magnetic fields’ complex effect resulted in the gallic and salicylic acid content increase by 14 % and 71%, respectively, compared to the untreated variant. The chlorogenic, salicylic and gallic acids’ active synthesis was observed 72 hours after the magnetic treatment with a frequency from 3.2 to 51 Hz. There was a tendency for the amount of the phenolcarbonic acid to decrease 14 days after the magnetic treatment, except for the variant with the pulsed and rotating field treatment.

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Currently, about 20 viral diseases are known on strawberry in the world that can reduce the yield and its quality. According to the results of previous studies in the Moscow region, the prevalence of viruses on strawberries was: Arabis mosaic virus (ArMV) – 14 %, Raspberry ringspot virus (RpRSV) and Strawberry latent ringspot virus (SLRSV) – 16 %, Tomato black ring virus (TBRV) – 25 %. Viruses mainly spread in agrocenosis with infected planting material, with tools, with pollen and seeds, nematodes - longidorids (Xiphinema diversicaudatum – ArMV and SLRSV vector, Longidorus elongatus – RpRSV and TBRV vector). According to published data, the harmfulness of viruses on plants of strawberries was to reduce the number of repens by 6-40 %, outlets by 10-40 %, and ovaries by 30 %. The aim of the study was to study the species composition of viruses on strawberries to identify candidates for the nuclear plants. In serological tests, a sandwich ELISA was used according to the method “Diagnosis of pome and stone crops viruses by ELISA and PCR” (2008), for analysis, diagnostic kits from ‘Loewe’ (Germany) were used. Leaves were taken as samples. The analysis results were recorded on a ‘Stat Fax 2100’ tablet photometer at a wavelength of 405 and 630 nm. The species composition of viruses was studied on strawberry varieties and hybrids under ex situ conditions. The total prevalence of viruses was 29 %. 188 candidates for nuclear stock plants of 17 varieties and 2 hybrids of strawberry were revealed. No viruses were detected on varieties Barynya, Induka and promising hybrids 34-34-5 and 3-372-1, which may be associated with a low percentage of transmission of nepoviruses with seeds. After confirming the virus-free status of strawberry plants by PCR, they will receive the category of “nuclear stock plant”.

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Relevance. Viral diseases can significantly reduce the yield of stone fruit crops. More than 30 viruses have been characterized on stone fruits crops, among which the most harmful are Plum pox virus (PPV), Prunus dwarf virus (PDV), Prunus necrotic ringspot virus (PNRSV), Cherry leaf roll spot virus (CLRV), Apple chlorotic leaf spot virus (ACLSV). Viral diseases monitoring is essential for controlling the viruses prevalence and choosing a control strategy. In the absence of healthy plants of a certain variety, health improvement is carried out using laboratory methods, including thermotherapy. Sanitation methods need to be improved in relation to the culture characteristics and the virus type. Of considerable interest is the development of techniques that reduce the viruses concentration when growing stone fruit trees in the field.Methods. During 2016–2020 using the ELISA (“Loewe” diagnostic kits) diagnostics of viruses on varieties and clonal rootstocks of cherry, sweet cherry and plum (660 plants) was carried out in the conditions of the Moscow region. For plant health in 2019–2021 used thermotherapy for 3 months. To study the effect of Pharmayod (“Farmbiomed”) on viruses in open ground, 24 plum plants of 5 varieties were treated with this drug at a concentration of 0.3 ml/l.Results. The total prevalence of viruses on cherries varieties was 44%, sweet cherries — 40%, plums — 59%, on clonal rootstocks — 46, 55 and 56% respectively. The highest incidence of PNRSV and PDV viruses has been established. Cherry plants of 11 varieties, free from the main harmful viruses, 4 varieties of sweet cherries, 12 varieties of plums and 9 forms of clonal rootstocks were revealed. The use of the Pharmayod on plum trees in the open field contributed to a decrease in the infection index of the studied viruses. Plum plants in a heat chamber were characterized by a higher survival rate and growth parameters in comparison with cherry and sweet cherry. After the completion of thermotherapy, a significant decrease in the index of infection in plants was noted.