The aim of the study is to find out the features of forming the quality of pollen grains, namely their size and viability, depending on the growing conditions and varietal characteristics of switchgrass. The research deals with the peculiarities of millet pollen grains formation, depending on the conditions of vegetation and varietal composition, as the pollen quality – its size and viability – affects the seeds germination. It was established that the pollen quality depended both on the

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... ons of the growing season and varietal composition. Thus, in the 2018 growing season the weather conditions in the flowering phase (July) were favorable for the viable pollen formation, and high temperatures in August, exceeding 35 oC after 11:00 am at the absence of precipitation affected the viability of the pollen. In all the varieties, the viability of pollen was low. The most viable pollen was in the Morozko variety and the least viable – in the Cave-in-Rock variety, which negatively affected the seed germination. Pollen grains are spherical in form and colorless. They were not uniform in size both depending on the genotype and the growing conditions. In 2018 the pollen grains size ranged from 29 to 60 microns, in 2019 – from 5.2 to 57.2 microns. In 2019, the smaller pollen formed compared to 2018 due to high average daily air temperatures that exceeded average daily long-term values and due to significant moisture deficiency. Millet pollen is not homogeneous, depending on the both genotype and vegetation conditions. In 2018, which was favorable for pollen formation, the size varied from 29 to 60 microns, and in the less favorable 2019, it was smaller and ranged from 5.2 to 57.2 microns. The largest size of pollen grains formed in the Sunburst variety compared to other varieties. The most uniform – 85.3 % of the total amount – was the pollen in the Cave-in-Rock variety. Key words: pollen grains, quality, pollen size, viability, pollen form, variability, uniform.