Purpose. Determine the effect of plant densities and the use of Organic-balance biological preparation on growth, development of photosynthetic potential and seed yield of maize lines, parental components of perspective hybrids (‘Arabat’, ‘Skadovskyi’, ‘Kakhovskyi’, ‘Azov’, ‘Chonhar’, ‘Hileia’ etc.) under conditions of drip irrigation. Methods. Field, morphometric, statistical. Results. In the flowering phase, the maximum differences in the area of the assimilation surface were observed between the maize lines and between variants using different plant densities and Organic-balance biological preparation. The largest indicator of the area of the assimilation surface was at the mid-late line DK445 for a standing density of 70 thousand plants/ha and the use of organic preparation Organic balance – 0.489 m2/plant. Organic-balance biological preparation had a positive effect on the dynamics of the area of the assimilation surface of the lines, had provide an increase of 0.04 m2/plant or 9.5% over individual phases of development compared to untreated control. The maximum value of the net productivity of photosynthesis – 6.78 g/m2 per day, was obtained from the FAO 420 line at a density of 70 thousand plant/ha, in the FAO 350 line was less by 4.3% with a maximum at a density of 80 thousand. plants/ha. For the FAO 290 line, the optimal plant density was 90,000 plants/ha. It was found that the genotype of the line with a share of influence of 81.2 and 85.2%, respectively, is predominantly influenced by the plant leaf area and the net productivity of photosynthesis. The influence of the organic preparation Organic-balance on these indicators was less and amounted to 13.3 and 12.3% respectively. The least influence on photosynthetic parameters was carried out by the density of phytocoenoses (the proportion of influence of 5.5 and 2.5%). Genotype with 82.2% share had the greatest influence on the seed yield of the lineage-parental components of maize hybrids. Part of the impact of the organic preparation Organic balance was 4.0%, plant density – 5.3%. The maximum seed yield of the FAO 290 line was obtained at a density of 90 thousand. growth./ha and organic drug treatment Organic-balance and amounted to 5.15 t/ha. The FAO 350 line showed the highest yield at a stand density of 80,000. growth/ha and treatment with organic drug Organic-balance – 5.46 t/ha. FAO 420, the highest seed yield, formed at a stand density of 80,000 plants/ha – 6.58 t/ha and treatment with organic drug Organic balance – 7.08 t/ha. Organic Balance treatment increased the seed yield by an average of 8.1%. Conclusions. Photosynthetic indicators of maize lines mainly depend on the genotype. Phytocenosis density and treatment with biopreparation have a much smaller effect. Under irrigation, the maximum seed yield was formed by the FAO 420 parent line of 7.08 t/ha. The results obtained indicate that in order to plan the production of seed material of maize lines, which are the parent components of hybrids, their genotypic features, the response to the density of phytocenoses and biological preparation with growth-stimulating action must be taken into account.