Assessment of the resistance of walnut forms to marsoniosis in arid conditions of the lower Volga Region

Walnut (Juglans regia L.) is one of the most widespread nut crops, widely used all over the world. One of the most dangerous and widespread diseases of the walnut is marsoniasis or brown spot, the causative agent of which is the marsupial fungus Marssonina juglandis . If there is a lot of precipitation in the first summer months, the disease progresses and can lead to the loss of more than half of the crop. The disease mainly affects the shoots, leaves and fruits of the walnut. The purpose of the work is to select the most promising genotypes based on long–term field studies of the resistance of walnut forms to marsoniosis for further use in breeding. The objects of research are 17 promising forms. The study took place in 2021-2023 on the territory of the orchard of the Federal State Budgetary Scientific Institution "Caspian Agrarian Federal Scientific Center of the Russian Federation Academy of Sciences ". The experiment was started in the spring of 2019 on an area of 0.21 hectares with annual seedlings. As a control, the local form of the Krupnoplodny nut (Volgograd) was used, which is most suitable for the geographical origin of the study region. The assessment of the degree of damage to walnut forms by marsoniosis was carried out on the basis of a methodology using a 5-point scale. 9 forms of walnut resistant to brown spotting have been identified: Ideal, 7 CSC 2000, Wen-185, Chili rounded, Elongated (Volgograd), Ideal SI 1-2, Ideal SI 2-6,Xingling, Large-fruited (Volgograd), among them Ideal, 7 CSC 2000, Wen-185 belong to the group of immune or highly resistant with an incidence rate of less than 1 point. These forms of walnut are promising for further study and breeding use.