Relevance. One of the most common diseases of potatoes and other nightshade family species is late blight caused by a pathogenic oomycete of the Phytophthora infestans (Mont.) de Bary. At least 100 species of phytophthora have been described in nature, affecting a wide range of plant species. The phytophthora population is heterogeneous and is represented by races, as well as different types of mating. This leads to a rapid adaptation of the pathogen and the emergence of new, more aggressive, and resistant races. Phytophthora is a parasite, the damage from which cannot be avoided within the organic farming framework. Therefore, it is particularly important to know the pathogenesis and racial composition of phytophthora in each individual region of Solanaceae cultivation.Research methodology. Differentiation and collection of material from the natural population were carried out using potato varieties with known R-genes in the genome. Isolation and introduction into the culture were carried out from leaves with the dampening chambers method, followed by cultivation on nutrient media. The pathogen was identified by microscopic analysis. Culture filtrates were obtained on the liquid nutritious medium, followed by liquid filtration and autoclaving. Phytotoxic activity was determined by the effect on the seedlings of the nightshade, grass, and pea families by the standard method. Molecular genetic analysis of the isolates was carried out by ISSR analysis; the primer, amplification mixture, and temperature profile of the reaction were selected according to the literature data; the calculation of genetic characteristics was carried out using POPGENE software packages.Results. Samples of seven Phytophthora infestans isolates were collected and introduced into culture. As a result of in vitro cultivation, morphological differences were revealed, expressed in the structure and color of the mycelium, the shape of the colonies, the nature of sporulation, the color of the reverse, and the medium under the colonies. The genetic differences of the natural phytophthora material introduced into the culture, collected from potato varieties with single resistance genes (R1, R3, R4), were revealed. Differences in the phytotoxic activity of the studied isolates' cultural filtrates were revealed. The isolated isolates demonstrate differentiation at the phenotypic, genetic and physiological levels, which allows us to speak about their belonging to races.

Relevance. Common buckwheat is one of the most important cereal and melliferous crops being in demand both in Russia and overseas. Despite the fact that buckwheat has lower sus- ceptibility to infectious diseases in comparisons with other grain and cereal crops, research on its pathogens is a topical issue considering a high disease rate for this crop in Primorsky krai. Materials and methods. The study on pathogenic composition was conducted in selective crop rotations of FSBSI “FSC of Agricultural Biotechnology of the Far East named after A.K. Chaiki” at the territory of Ussuriysky district in Primorsky krai. Indeterminate (Izumrud, Pri 7, Bashkirskaya krasnostebel’naya) and determinate (Dikul) buckwheat varieties were used for the study. Fungi were isolated from rhizoplane using water washing technique, from soil and rhizosphere via the dilution method, from leaves and root systems by accumulation in a moist chamber with subsequent transfer of culture onto selective medium. Fungal isolates were cul- tivated on toxigenic medium (Myro) to determine their phytotoxicity. Phytopathogenic activity of living cultures was evaluated on potato sucrose agar according to the modified method of Chelkowski and Manka . All experiments were conducted in accordance with established methods.Results. Culture filtrates of F. avenaceum and F. graminearum isolates, obtained from different anatomical parts of common buckwheat, were characterized by low toxicity, and culture filtrates of F. oxysporum isolate were highly toxic. Phytotoxicity of pathogens manifested itself not only in decrease in laboratory germination ability of buckwheat seeds, but also in inhibition of buckwheat sprout development. It proved that metabolites exerted a prolonged effect on sensitive plants. F.avenaceum, F. oxysporum and F. graminearum have pronounced phy- topathogenic and aggressive properties in relation to buckwheat and test-plants in the laboratory conditions. The sum total of their studied phytotoxic properties is convincing enough to consider them potentially hazardous to buckwheat for wilt disease development.