In order to prevent crop yield losses from the most dangerous and economically important pathogenic organisms, it is necessary not only to monitor the virulence gene pool, but also to study the nature of pathogen variability and determine the potential for the emergence of new genes and races. This requires centralized collections of fungal cultures characterized by a set of stable strains to provide for phytopathological, immunological, breeding, genetic, toxicological, parasitological and other studies. The State Collection of Phytopathogenic Microorganisms of the ARSRIP is the State Depository of Phytopathogenic microorganisms that are non-pathogenic to humans or farmed animals. Currently, it has more than 4,500 accessions of plant pathogenic strains of fungi, oomycetes, bacteria, viruses, phytoplasmas, and the collection is updated annually. For this purpose, the study of the inter- and intraspecific genetic diversity of genus Fusarium was carried out in agricultural systems of the Krasnodar Territory. In 2020, the State Collection of Phytopathogenic Microorganisms was supplemented with 13 strains of Fusarium fungi isolated from tissues of winter wheat plants collected in several locations of the Krasnodar region. The complex of Fusarium fungi revealed on winter wheat usually included Fusarium oxysporum, F. culmorum, F. lolii, F. graminearum, F. fujikuroi, F. sporotrichioides, etc. The effect of the preceding crop on the frequency of Fusarium species isolated from winter wheat was observed. After series cloning of collected isolates, 21 strains of different fungal species characterized by stable morphology traits and known pathogenic and phytotoxic properties were selected for collection replenishment. Significant differences in pathogenic activity were revealed between fungi belonging to either the same or different species; the manifestation of this activity varied from the absence of any effect of spore suspensions on seedling development to a complete inhibition of their growth. The phytotoxic activity towards wheat seedlings varied from medium to high. Species possessing a high intensity of phytotoxic activities are the most dangerous for wheat, since they promote accumulation of dangerous phytotoxins in plant tissues.

Corn is one of the main crops of modern world agriculture. It ranks f irst in terms of gross grain harvests and second in terms of acreage, ceding only to the main grain crop of the globe, wheat. The problem of increasing the production of grain and green mass of corn remains one of the urgent tasks of agricultural production. High potential yields very often remain untapped due to diseases, direct losses from which are estimated at 20–50 %. The purpose of this work was to study the species composition of micromycetes on corn collected in different phases of vegetation in May-July 2020 in the Voronezh region, to identify phytopathogenic genus Fusarium fungi, to study pathogenic and phytotoxic strains of the fungi to replenish the collection of the All-Russian Scientific Research Institute of a Phytopathology. Preservation of infectious material of fungi from the genus Fusarium is of no small importance for phytopathological, immunological, breeding, genetic and toxicological studies. As a result of the mycological studies carried out, a lot of fungi isolates from the genera Fusarium, Aspergillus, Cladosporium, Curvularia, Penicillium, Rhizopus, Periconia, Pythium, Trichothecium, etc., isolated from the affected roots, stems and ears of corn in the Voronezh region in 2020 were identif ied. Fungi isolates from seven taxonomic groups: Fusarium fujikuroi Nirenberg (F. moniliforme, F. verticillioides), Fusarium oxysporum Schltdl., Fusarium culmorum (Wm.G. Sm.) Sacc., Fusarium graminearum Schwabe, Fusarium heterosporum Nees & T. Nees (F. lolii ), Fusarium roseum Link (F. sambucinum), Fusarium sporotrichioides Sherb. were tested for pathogenicity and phytotoxicity on seedlings of plant-testers. It has been shown that pathogenic and phytotoxic activity in fungi varies signif icantly between Fusarium species and within the same species. The greatest danger to corn is represented by the species F. sporotrichioides, F. graminearum, F. culmorum, F. fujikuroi, F. oxysporum, F. heterosporum, which have a high intensity of phytotoxic activity associated with the fact that they contribute to the synthesis and accumulation of dangerous toxins in plant tissues. As a result of the conducted studies, 55 strains of fungi from the genus Fusarium belonging to seven species were selected. The isolates, stable in morphological and cultural characteristics and studied for pathogenicity and toxicity, were placed for long-term storage in the Russian State Collection of Plant Pathogenic Microorganisms and Cultivars for Identif ication of Phytopathogenic Microbial Strains at the All-Russian Scientif ic Research Institute of a Phytopathology.

Relevance. Currently, the relevance of studying to identify the ability of many micromycetes to synthesize phytotoxic substances that reduce seed germination and lead to huge losses in the yield of strategic agricultural crops is increasing. To solve the problem, the development of new methodological approaches is required, which is significant for immunologists and phytopathologists.The purpose of this work is to determine the phytotoxic activity of micromycete strains from the genera Fusarium, Alternaria, Bipolaris, parasitizing on all agricultural crops cultivated in Russia.Materials and methods. The strains, the methods of their cultivation, the bioassay method were used, and the statistical processing of the results obtained was carried out. A modification of some methodological approaches for assessing the phytotoxicity of micromycetes has been carried out. The selection of representative concentrations of culture fluid filtrates (FCF) of strains for phytotoxicity evaluation was carried out.Results. A correlation was established for all variants of the experiment between two independent parameters: the development parameters of wheat seedlings and the concentration of cultural liquid filtrates. New results have been obtained on the study of the phytotoxic activity of 70 strains of hemibiotrophic micromycetes and the optimal concentrations of fungal FAs for classifying fungal strains into toxicity groups have been established. The most variable toxicity values were found when using a 40% solution of FCL. It was shown that, under these conditions, fungal strains can be divided according to the degree of toxicity into significantly different groups. This circumstance is an important reason for including strains of micromycetes with certain toxicity properties in the State Collection of Phytopathogenic Microorganisms. Fungal strains are necessary and appropriate for use in breeding to create resistant and tolerant varieties to phytopathogens from the genera Fusarium, Alternaria, Bipolaris.Conclusion. New methodological approaches have confirmed that the most variable toxicity values were found with the use of FCF in a ratio of 2:3. This concentration of FCF strains are divided into 4 groups with characteristic differences in the degree of toxicity, which is an important reason for including such strains of micromycetes in the State Collection of Phytopathogenic Microorganisms and will be further used in breeding to create resistant and tolerant varieties of agricultural crops.