Fruit growing
and viticulture of South Russia

Annotation

The results of studies on the intensity of downy mildew development in the conditions of the vineyards of the Don ampelographic collection in 2019-2021 are presented. The preservation of wintering forms of mildew was facilitated by the weather conditions of the dormant periods i n 2019-2021: the absence of low freezing temperatures and sufficient humidity (61-85 %). The air temperature in the autumn-winter periods during the years of research was significantly higher than the average long-term values (the sum of negative temperatures ranged from 119.4 �� to 274.3 ��). Under such conditions, the oospores of the pathogen, germinating at the beginning of the growing season, produce an inoculum for primary infection of plants. Phytomonitoring of the infestation of various varieties with downy mildew under epiphytotic conditions in 2021 made it possible to identify the most resistant varieties for their further use as donors of downy mildew resistance. During the growing seasons in 2019, 2020, the increased temperature, compared with the average annual values, and low humidity contributed to the depressive development of downy mildew. When the hydrothermal coefficient was from 0 to 0.5, the plants of 70-80 % of varieties had no signs of downy mildew. The intensity of disease development in other varieties did not exceed 2.5 points. In 2021, in all growing months, with the exception of July, there was a shortage of precipitation. Despite this, the increased air humidity in May-July with a hydrothermal coefficient of 0.8-1.2 contributed to the intensive development of downy mildew. As a result, 12 % of the varieties of the Don ampelographic collection showed the highest resistance to downy mildew (up to 2 points): Tavrosi; Pochatochnyy; Ol'khovskiy; Nakutvneuli; Kosorotovskiy; Grdzelmtevana. The intensity of the infestation from 2 to 3.5 points was found in 78 % of the varieties. The least resistance to downy mildew (more than 3.5 points) was manifested in 10 % of varieties: Sypunchernyy; Pukhlyakovskiy chernyy; Megrabuyr; Bessergenevskiy � 1; Belobulanyy.