ORIGINAL PAPER Production of phytohormones, siderophores and population fluctuation of two root-promoting rhizobacteria in Eucalyptus globulus cuttings Katy Dı ´az Peralta • Ta ´mara Araya • Sofı ´a Valenzuela • Katherine Sossa • Miguel Martı ´nez • Hugo Pen ˜ a-Corte ´s • Eugenio Sanfuentes Received: 18 October 2011 / Accepted: 6 January 2012 / Published online: 15 January 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Vegetative propagation by stem cuttings and mini-cuttings has been used worldwide for growing Eucalyptus plants. However, clones and hybrids of this plant present a great variability in their rooting capacity, apart from a gradual decrease in the rooting potential due to the ontogenetic age of the mother plant. Several studies have demonstrated that some bacteria promote plant growth and rooting through the action of direct and indirect mechanisms that are not still completely clear. Considering this, the objective of this study was to assess the production of auxins, abscisic acid and siderophores in Bacillus subtilis and Stenotrophomona maltophilia, which in pre- vious studies increased rooting of E. globulus cuttings. Additionally, the population of these bacteria in the rhizosphere, superficial tissues of the stem-base and callus of the mini-cuttings was identified, and quantified by real-time PCR. Only S. maltophilia produced IAA in the presence of tryptophan; none of the bacterial strains pro- duced ABA, but both produced siderophores. A compara- tive analysis of the separation profiles showed that there is a diverse microbial community in the rhizosphere, and only S. maltophilia was capable of keeping its population at a density of 2.03 9 10 7 cells/mg in different tissues of the mini-cuttings. The results would indicate that the rooting stimulus in E. globulus could be related to the action of one or several mechanisms such as the production of auxins and siderophores, and it could also be associated with the ability of bacteria to stay in the rhizosphere or in plant callus tissues. Keywords Stenotrophomona  Bacillus  Phytohormones  Siderophores  Rhizosphere  DGGE Introduction Currently, Eucalyptus is the second exotic genus impor- tance in Chile with a total planted area of 661,394 ha, Eucalyptus globulus being the most important with 471,743 ha. This specie has a valuable economic role in the forestry industry in the country because of their wide dis- tribution (including a range of climate and soil), their ability for the manufacture of quality paper, and their rapid growth (INFOR 2008). The worldwide forest breeding programs are based on the clonal plantation of species from the genus Eucalyptus, employing vegetative propagation using macro and micro- propagation techniques. However, vegetative propagation in some species does not provide the best reproduction system due to particular effects of endogenous and exog- enous factors on the mother plant, alterations of root K. D. Peralta  E. Sanfuentes Forest Pathology Laboratory, Biotechnology Center, University of Concepcio ´n, Concepcio ´n, Chile K. D. Peralta (&)  H. Pen ˜a-Corte ´s Biotechnology Center ‘‘D. Alkalay L’’, Universidad Te ´cnica Federico Santa Marı ´a, Valparaiso, Chile e-mail: katy.diaz@usm.cl T. Araya  K. Sossa Biofilms and Environmental Microbiology Laboratory, Biotechnology Center, University of Concepcio ´n, Concepcio ´n, Chile S. Valenzuela Molecular Biology and Genomics Laboratory, Biotechnology Center, University of Concepcio ´n, Concepcio ´n, Chile M. Martı ´nez Microbiology Laboratory, Faculty of Biological Sciences, University of Concepcio ´n, Concepcio ´n, Chile 123 World J Microbiol Biotechnol (2012) 28:2003–2014 DOI 10.1007/s11274-012-1003-8