Applied Soil Ecology 55 (2012) 44–52 Contents lists available at SciVerse ScienceDirect Applied Soil Ecology journa l h o me page: www.elsevier.com/locate/apsoil Diversity of plant growth-promoting rhizobacteria communities associated with the stages of canola growth Roberto Farina a , Anelise Beneduzi a , Adriana Ambrosini a , Samanta B. de Campos a , Bruno Brito Lisboa b , Volker Wendisch c , Luciano K. Vargas b , Luciane M.P. Passaglia a,∗ a Universidade Federal do Rio Grande do Sul, Instituto de Biociências, Departamento de Genética, Av. Bento Gonc ¸ alves, 9500, Caixa Postal 15.053, 91501-970 Porto Alegre, RS, Brazil b Fundac ¸ ão Estadual de Pesquisa Agropecuária (FEPAGRO), Rua Gonc ¸ alves Dias 570, 90130-060 Porto Alegre, RS, Brazil c Department of Genetics of Prokaryotes, Bielefeld University, Universitätsstraße 25, 33594 Bielefeld, Germany a r t i c l e i n f o Article history: Received 17 October 2011 Received in revised form 22 December 2011 Accepted 28 December 2011 Keywords: Canola PGPR abilities Bacterial diversity Inoculants Plant growth response a b s t r a c t Plant growth-promoting rhizobacteria (PGPR) stimulate the growth of their host plant and the presence of the plant clearly has a significant effect on rhizospheric bacterial community structure. In this study, cultivable bacteria associated with soil, rhizosphere and the roots of canola (Brassica napus) were isolated and identified by amplifying the V6–V8 region on the 16S rDNA sequence, in order to verify if possible changes in the microbial communities were associated with some stages of crop rotation and canola growth. Several PGP activities of all isolates were also evaluated. The bacterial richness associated to the rhizospheric soil of canola at the rosette stage was more than 20% larger than the other stages indicating that the microbial community structure was influenced by seasonal variation. There was also a rela- tionship between bacterial diversity and monthly rainfall. Agrobacterium, Burkholderia, Enterobacter, and Pseudomonas were the most abundant among all the bacterial genera identified. Several of those bacteria could produce indolic compounds and siderophores, to solubilize phosphate, and some could also fix nitrogen. Some of the isolates tested for growth-promoting effects of bacterial treatment in canola were able to promote plant growth. The presence of specific PGP traits suggests that these particular organisms can promote plant growth by more than one mechanism and that some of these strains should be tested in further field inoculation experiments. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Plant growth-promoting rhizobacteria (PGPR) stimulate the growth of their host plants (Vessey, 2003). These bacteria can colo- nize either only the rhizosphere (epiphytic bacteria), or also inside the roots (endophytic bacteria) (Glick, 1995). Endophytic bacteria can be either associative or facultative. Facultative endophytes live in the spaces between the cells of the root cortex (Elmerich and Newton, 2007; Kobayashi et al., 1995), whereas associative bacte- ria can establish a symbiotic relationship with plant cells, living inside the cells in specialized root structures called nodules (Gray and Smith, 2005). PGPR stimulate plant growth directly or indirectly. Indirect stimulation occurs when PGPR prevent the deleterious effects of phytopathogenic microorganisms, while direct plant growth ∗ Corresponding author at: Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸ alves, 9500, Caixa Postal 15.053, Prédio 43312, sala 207b, Porto Alegre, RS, CEP 91501-970, Brazil. Tel.: +55 51 3308 9813; fax: +55 51 3308 7311. E-mail address: lpassaglia@terra.com.br (L.M.P. Passaglia). stimulation occurs when PGPR synthesize some plant-growth substances or facilitate the uptake of certain nutrients. Direct stimulation involves nitrogen fixation (performed by diazotrophic organisms), solubilization of phosphate, production of phyto- hormones (such as auxin and cytokines), and production of siderophore that helps the transportation of ferric iron into plant cells (Ghosh et al., 2003). While the rhizobacteria may benefit the plant, the presence of the plant clearly has a significant effect on rhizosphere bacterial community structure due to differences in root exudation, rhizode- position in different root zones and the growth stage of the plant (Di Cello et al., 1997; Smalla et al., 2001; Dunfield and Germida, 2003; Houlden et al., 2008). Furthermore, other factors might influence the composition of the microbial community in the rhizosphere, such as cropping practices (like crop rotation) and seasonal change (Di Cello et al., 1997; Lupwayi et al., 1998; Smalla et al., 2001; Dunfield and Germida, 2003). Canola is an option for ground cover plant for crop rotation and the production of oil and both as food and biodiesel (Schuchardt et al., 1998; Tomm, 2005). Among the available technologies that increase crop productivity and decrease the use of nitrogen fertil- izers is the use of diazotrophs because of their abilities to promote 0929-1393/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2011.12.011