Ecological Systems and Devices Annotation << Back Research of the Toxicity of Microalgae and Cyanobacteria and Optimization of Their Cultivation Conditions for the Purpose of Developing a Biological Product for Agriculture Bataeva Yu.V., Andreeva M.P., Bataeva A.D., Trofi mov A.V., Kurmaliev I.R., Vagin Ya.D., Bareeva D.D The phytotoxicity of a suspension of green algae of the genus Scenedesmus, cyanobacteria of the genus Anabaena, and soil cyanobacterial communities was studied in laboratory conditions on radish. The highest germination rate was found in the experimental variant treated with algae of the genus Scenedesmus – 100 %. Treatment of seeds with cyanobacteria showed a high germination result of 98 % and 95.3 %, in comparison with a negative control of 88.7 % (treatment with tap water) and positive controls – epin (93.3 %) and HB-101 (91.3 %). In an experiment with tomatoes at the early stages of plant development, the highest germination rate was also found in the variant treated with Scenedesmus algae – 67 %. In a test with daphnia, green microalgae were found to be non-toxic. Cultivation conditions for the effective increase in biomass of green algae of the genus Scenedesmus have been studied. The optimal conditions for the development of algae turned out to be climatic conditions and natural lighting with shaking, under which the number of cells was the greatest 3.3–3.7 × 103 thousand cells/cm3 . Keywords: green algae, cyanobacteria, Scenedesmus, Anabaena, cultivation, phytotoxicity, toxicity. DOI: 10.25791/esip.1.2024.1427 Pp. 62-69.