Solanum tuberosum L. is susceptible to 40 different virus species and 2 viroids. To prevent plant viruses from spreading in field conditions, it is necessary to have reliable data on the species composition of plant reservoirs of viral infection, the total activity of insect vectors, and possible ways of virus transmission in a particular territory of seed material production. Attention should be paid to the factors that facilitate and hinder the disease development in crops and to disease symptoms in different potato varieties. Manifestations of viral infections were monitored on every plant from the sample at the stages of initial growth, bud formation, and flowering and before the removal of potato haulms. Insects were collected using standard entomological method. The total RNA was isolated employing commercial kits for the extraction of nucleic acids from plant material “PhytoSorb” (Syntol Llc) and the benchtop automated extraction instrument KingFisher Flex (ThermoScientific) with magnetic particles. Plant viral infection was observed to accumulate if potato planting material was not renewed. The tested potato plants contained mixed viral infection, which consisted of viruses from mosaic group: PVY, PVX, PVM, PVS PVA, as well as PSTVd and PLRV. Without the renewal of seed potatoes, the concentration of plant viruses in an agroecosystem rises and causes secondary infections in potato plants. The research identified the main insect-vectors in the agroecosystem of potato fields: insects from genera Cicadella, Henosepilachna vigintioctomaculata, Dolycoris baccarum, Mythimna separata, Lygus pratensis, and Rhopalosiphum padi. Many wild weeds serve as fodder plants for insect vectors facilitating the accumulation of plant viruses in agroecosystems. It was established that perennial weeds were the main plant reservoirs of dangerous viral infections, e.g. Sonchus arvensis and Taraxacum officinale. We determined that Trifolium pratense typus L., Chenopodium album L., Plantago major L., Barbarea vulgaris W.T. Aiton, and Ambrosia artemisiifolia L. were the reservoirs of PVY. All these factors can lead to an epiphytotic situation.

Relevance. Oxidative reactions (based on peroxidase activity, POX and polyphenol oxidase, PPO; hydrogen peroxide content) that occur in response to infection or reinfection of the off-spring of infected plants depend on the type of host-virus interaction (sensitive, tolerant, stable) and the nature of the interaction with viral infection (primary infection, reinfection of second and third generations).Results. Reinfection with tomato aspermy virus (TАV) or tobacco mosaic virus (TMV) of the off-spring of third infected tomato generation caused a significant decrease in POX activity compared to successive generations of infected plants (G2) for Craigella (Tm-22/Tm- 22) and S. pimpinellifolium genotypes or an increase for Rufina and Craigella (Tm-1/Tm-1) ones. In genotypes containing resistance genes, Rufina and Craigella, no differences were observed in PPO of TMV primary infection and control, while significant differences were found in case of TAV (susceptibility). As a result of TMV infection, the sensitive (Elvira) and tolerant (S. pimpinellifolium) genotypes showed an increase in PPO values compared to the control. At the same time, in most genotypes primarily / secondarily infected with TAV or TMV, statistically significant differences were revealed in the activity of POX or PPO, as well as the accumulation of hydrogen peroxide in plant leaves, which indicates specific protective reactions of the genotypes.

Scientific relevance. Plant viruses cause a significant economic loss to potato production, especially if plants are infected at early growth stages and infections are mixed. Viral diseases reduce both yield and quality of harvested crops. Detection and identification of plant viruses are key important to prevent their spreading and to achieve potential yield predetermined by characteristics of varieties.Research methods. Seven potato varieties, bred in Russia and overseas, were used in the field experiment: Smak, Avgustin, Yantar, Laperla, Labella, Red Lady, Sante, Belmonda. Viral infection rate was measured by the percent of plants with symptoms to the total number of plants. In addition to infection frequency, a disease rate was described after visual estimation. Total RNA was isolated from the collected leaves according to Bekesiova I. et al. 1999 [13]. Qualitative and quantitative estimation of plant viruses in the samples were conducted by single-step real-time RT-PCR with fluorescent detection with the Applied Biosystems QuantStudio 5 and commercial kits “Potato Virus X, Y, M, L, S, A, PSTVd-RT” (Syntol Company) according to the official protocol of the kits.Results. As a result of our research, symptoms of mixed viral infection were described for potato varieties depending on concentrations and proportions of these viruses in a plant. Mixed viral infection in the potato field in Primorsky Krai comprised PVY, PVX, PVA, PVS, PVM, also PLRV and PSTVd.