Factors determining affecting the development of Phytophthora infestans on a tomato in the open ground

Relevance and methods. For the Non-chernozem zone, the main factor for the active development of late blight is the low air temperature and its sharp fluctuations during the day, contributing to the formation of increased air humidity and drip-liquid moisture on the plants. In the Moscow region, the causative agent of late blight is manifested almost annually. Populations of Phytophthora infestans are represented by the To and T1 races. Epiphytotic development was observed periodically (1977-1979, 1982, 1986, 1996-1999, 2000, 2001, 2003-2004, 2008-2009, 2013, 2014, 2015, 2016, 2017, 2019) and was provided by the virulent T1 race. Observations showed that epiphytotic situations arose in those years when the minimum air temperature was below long-term average values, and relative humidity and precipitation exceeded them. With a deviation from the norm in the direction of increasing temperature, decreasing rainfall and relatively low humidity, years were observed with a depressive (1992, 1994) or moderate development of the disease (1980, 1981, 1983, 1985, 1987-1991, 2002, 2005-2007, 2010-2012, 2018). Results. As a result of breeding work, a Grot tomato-tolerant tomato variety was obtained, on the basis of which varieties with high resistance Grand, Dubok, Gnom, Chelnok, Patris, Geya, Zolushka, Perst, Severyanka, Blagodatny were obtained. In the general collection of VIR as a source resistance to leaf spot pathogens were registered: Geya (v.k. 14839), Slavyanka (v.k. 14840), Patrice (v.k. 14841), Rossiyanka (v.k. 14842), Krepysh (v.k. 14843), Sibiryachka (v.k. 14444) and line 1079-94 (v.k. 14845) donors, in addition to their high resistance to late blight, have excellent economic characteristics.