This research was carried out to examine the effects of different doses of bacterial formulation comprised of a mixture of Bacillus megaterium TV-91C, Pantoea agglomerans RK-92 and Kluyvera cryocrescens TV-113C strains on the plant development and bract quality of poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch), which are one of the most important potted plants grown for their fleshy bracts of the horticultural sector. The study was carried out in a climate-controlled research greenhouse from 8 August 2018 to 15 January 2019 in Erzurum (Turkey). Rooted cuttings of poinsettia [E. pulcherrima Willd. ex Klotzsch cv. Christmas Feelings (CvF)] were used as plant materials in the study. Each of the solutions containing bacterial suspensions 52.5 (T1), 105 (T2), 210 (T3), 420 (T4) and 840 (T5) mL · L−1 of water was diluted 5 times with water and 200 mL · pot−1 was applied to the plant rhizosphere. This study revealed that positive changes incurred in plant height, main flower stem length, plant crown width, bract diameter, green leaf and bract leaf area, leaf total nitrogen content and nitrate reductase enzyme activity parameters in poinsettia plants with increasing doses of the bacterial formulation. This effect has reached the maximum level in the number of bracts, main flower stem length, bract diameter, nitrate reductase enzyme activity, plant fresh weight and maximal root length parameters with the T5 application which has the highest bacterial formulation concentration. The most efficient application of glutamine synthetase enzyme activity was determined as T4.
