This paper describes the results of a complex survey of prevalence and polymorphism of phytopathogenic fungus Cryphonectria parasitica in the Black Sea part of the area of sowing chestnut (castanea sativa). A comparative analysis of the situation with Cryphonecrosis in the Caucasus of the Russian Federation with the European one is given, and an assessment of the degree of threat of the pathogen to the Russian population of chestnut is given, as well as possible measures for the conservation of chestnut on the territory of the Russian Federation. The study obtained data on the level of genetic heterogeneity of the fungus in the studied areas and analyzed its virulent properties. Some areas of the CHV hypovirus genome detected in Cryphonectria parasitica strains in Russia and Turkey were analyzed, and the prospects of its use as an agent of biological control of cryphonecrosis in Russia were assessed.