Impact of PGPR Formulations Combined with Exogenous IBA Levels to Enhance Root Capacity in Poinsettia Cuttings

Abstract

The commercial production of poinsettias begins with the propagation of apical cuttings from stock plants. The aim of the study was to use bacterial mixtures prepared with PGPRs in the cultivation of stock mother poinsettia plants and determine an effective IBA dose to increase root development and root yield of cuttings prepared from these stock mother plants. Rooted cuttings of Euphorbia pulcherrima Willd.ex Klotzsch were used for planting stocks of mother plants. Eight different bacterial isolates were mixed in triple combinations to form 4 different bacterial formulations: (BI) formulation 1 (Paenibacillus polymyxa TV-12E + Pseudomonas putida TV-42A + Pantoea agglomerans RK-79); (BII) formulation 2 (Bacillus megaterium TV-91C + Pantoea agglomerans RK-92 + Bacillus subtilis TV-17C); (BIII) formulation 3 (Bacillus megaterium TV-91C + Pantoea agglomerans RK-92 + Kluyvera cryocrescens TV-113C); and (BIV) formulation 4 (Bacillus megaterium TV-91C + Pantoea agglomerans RK-79 + Bacillus megaterium TV-6D). In the first year, rooted cuttings of stock mother plants were dipped in liquid microbial solution (bacterial formulations) for 15 min and then planted in plastic pots. In the second year, the same bacterial formulations were freshly prepared and applied to the 1-year-old stock mother plants as irrigation water for the second time. Amounts of 0 (control), 1000, 1500, and 2000 mg L−1 IBA doses were used for rooting cuttings taken from the 2-year-old stock mother plants. In the experimental group treated with the BI bacterial formulation, the number of rooted cuttings (NR) increased by 14.26% and 19.00%, compared with the control, in response to IBA 1500 mg L−1 and IBA 2000 mg L−1 treatment, respectively. Compared to the mean root length of the cuttings in the control treatment, the mean root length of the cuttings in the BIV treatment increased by 18.83%. The mean root length values decreased with the increase in IBA doses. The highest value of the number of mean shoots (NAS) was in cuttings treated with BI + 1500 treatment, which was 1.93 times higher than the control. The highest nitrogen content (5.73%) was determined in the bract leaf samples of the BIV application, and an 81.33% nitrogen increase was detected in the related application when compared to the control. In terms of P, Ca, and Fe contents, higher values were obtained from the BIV application when compared to the control application. The highest values of K content were determined in BIII and BII applications. This study provides positive effects on the feedback of stock mother plants with PGPR to provide sprout production by cuttings technique. It has been revealed that lower IBA dose applications can be recommended for rooting cuttings taken from mother plants treated with the BIV bacterial formulation.