Ergot (Claviceps purpurea (Fr) Tul.) is a widespread rye disease. A strong development of the disease can reduce up to 60% of grain productivity and its quality. In the rye gene pool, there was found no samples with complete resis[1]tance to Cl. purpurea. Since 2016, six new winter rye varieties with a low content of water-soluble pentosans in grain have been approved for cultivation in Russia. It has been noticed that low-pentosan varieties are less affected by ergot. The harmful effect of the disease largely depends on the sclerotia parameters. The purpose of the current study was to characterize the development of ergot on the high-pentosan winter rye variety ‘Era’ and its low-pentosan analogue ‘Novaya Era’. There was estimated the infestation of the varieties, the size and weight of the formed sclerotia. It was found that with the same infection level, the infestation of the variety ‘Era’ was 48.5%, and that of the variety ‘Novaya Era’ was 18.1%. On the heads of high-pentosan rye there were formed full-fledged sclerotia with 15.97–23.55 mm in length and 2.68–3.83 mm in width. On the heads of low-pentosan rye ‘Novaya Era’ the fungus formed underdeveloped sclerotia, the mass of which was 4-8 times less than on the variety ‘Era’. The small size and weight of the horns facilitated their removal from the crop during threshing, and reduced rye grain infection with ergot. The frequency of low-pentosan plants occurring in the varietal population affects the infection rate of rye. The frequency of low-pentosan plants in the variety ‘Era’ is 43%, and in the variety ‘Novaya Era’ is 95%. The development of rye varieties characterized by a low content of water-soluble pentosans in grain is connected with breeding for resistance to Cl. purpurea.