Аннотация:n recent years, the frequency of Pythium leak of potato, caused by a soil pathogen Pythium ultimum, increased in many regions of Russia. This soilborn pathogen infects tubers in the field and storage facilities and also affects plant roots causing their rot. In spite of many publications about Pythium leak of tubers, data on the influence of this pathogen on the growth and development of potato plants are absent. In this study performed under greenhouse conditions, the effect of a pre-planting soil infection with P. ultimum on some morphometric traits of potato plants (cvs. Lorh and BP-808) was investigated, and the efficiency of a protective pre-planting treatment of soil with the Uniform (azoxystrobin + mefenoxam) fungicide was evaluated. The most negative influence of the pathogen presence in the soil was observed for plants of the middle-late cv. Lorh. For both cultivars (Lorh and BP-808), the pathogen caused reduction of the plant height (by 35 and 23%), root length (by 47 and 35%), and total yield (35 and 26%); in the case of cv. Lorh, a decrease in the germination rate and the number of stems per a plant were also registered (6 and 10%, respectively). A pre-planting soil application of the Uniform fungicide not only prevented the above-described negative influence of P. ultimum, but also provided a significant positive effect on the development of plants. In the case of such treatment, plants of cv. Lorh demonstrated increase in their height, number of stems, root length, and the total yield (24, 10, 29, and 29%, respectively) comparing to the control; for plants of the middle-early cv. BP-808, pre-planting Uniform application resulted in a significant increase in the root length and total yield (10 and 11%, respectively). Thus, the Uniform fungicide may be considered as an efficient tool to control Pythium-induced rot.