Gene postulation is one of the fastest and most cost-effective methods for identifying seedling leaf rust resistance genes in wheat cultivars. Many researchers use this approach to identify Lr genes in wheat cultivars. The purpose of our research was to identify seedling leaf rust resistance genes in 20 wheat cultivars from different breeding centers of Russia, Ukraine and Germany. Forty-two near isogenic Thatcher lines and 10 Puccinia triticina isolates were used for gene postulation. When assessing the infection types to cultivars and lines, a scale was used, according to Oelke and Kolmer. In 20 wheat cultivars 19 Lr genes were postulated: 2c, 3, 10, 3bg, 3ka, 14a, 17, 18, 23, 25, 26, 30, 33, 40, 44, 50, B, Exch, Kanred. The most common for cultivars was the Lr10 gene. In five cultivars, showing high field resistance, most postulated seedling genes (Lr2c, Lr3, Lr10, Lr14а, Lr26, Lr33) were not effective in the adult stage. It is possible that resistance of such cultivars is associated with APR genes, the postulation of which requires an expansion in the number and spectrum of P. triticina isolate virulence. Most of the studied cultivars (60%) have recently been entered into the register (2015–2019) and in the field show a stable or moderately susceptible response to P. triticina infection, despite the fact that the Lr genes postulated in them were not effective in the adult stage. The data obtained indicated a variety of genotypes of the studied cultivars, as well as the tendency of breeders to use the effect of pyramiding ineffective genes, which can prolong the resistance of the cultivar. Annual monitoring of varieties is necessary in each region, especially when reacting with a medium susceptible type (MS), which may indicate the initial stage of resistance loss.