Leaf-stem diseases of soybean on varieties of diferent ripenity groups in the conditions of the Amur region

The Amur region is the main producer of soybeans in the Russian Federation, where one of the significant phytosanitary problems of soybean cultivation technologies is leaf and stem infections. The susceptibility of soybeans to diseases varies greatly depending on weather conditions, used agricultural technology and the resistance of cultivated varieties. Since the soybean varieties, cultivated in the region, have significant differences in early maturity, it remains relevant to monitor leaf and stem infections and identify the degree of their development depending on the length of the crop growing season and the year conditions. The purpose of the study was to assess the influence of soybean variety by maturity groups and year conditions on the incidence of leaf-stem infections. Research was carried out in 2022 and 2023 in the Tambov district of the Amur region on 32 soybean varieties of domestic and foreign selection, belonging to 3 ripeness groups: early ripening, mid-ripening and late ripening. A phytopathological examination of soybean crops revealed Septoria blight (Septoria glycines T. Hemmi. Syn.), Cercospora blight (Cercospora sojina Hara), Ascochyta blight (Ascochyta sojaecola Abramoff. Syn.), downy mildew (Peronospora manshurica (Naum.) Syd. Syn.), purple Cercospora blight (Cercospora kikuchii (Matsuet Tomoyasu) Yardn) and angular bacterial spot. According to the indicator of disease incidence on soybean varieties of three ripeness groups, it was revealed that the incidence of downy mildew significantly, at the level of 90 %, depended on the variety ripeness group: mid-, and especially late-ripening varieties, were affected by the disease in both years an order of magnitude more strongly than early-ripening varieties. No significant influence of soybean varieties maturity groups on other infections was detected after the use of the fungicide, while analysis of variance according to the two-factor experiment scheme showed a significant influence of year weather conditions on the diseases incidence: Cercospora blight – at the level of 75.7 %, Cercospora purple blight – 77.1 %, Ascochyta blight – 98.5%. Both the ripeness group of soybean varieties and the year conditions influenced the bacteriosis incidence: the disease was more pronounced on early-ripening varieties, which were more populated by mites, the vectors of the disease pathogen, and was noted only in 2023. Analysis of variance according to the two-factor experiment scheme did not reveal a significant influence of varieties and year conditions on the incidence of Septoria blight, which indicates significant adaptations of the pathogen to weather factors and the physiology of plants from different ripeness groups, as well as the stable effectiveness of fungicidal treatment of soybean crops against Septoria blight.