Effect of plant growth-promoting rhizobacteria on root formation and growth of tissue cultured oil palm (Elaeis guineensis Jacq.)

Abstract

An experiment was conducted to enhance rooting initiation for oil palm shootlets by using diazotrophic rhizobacteria (locally isolated Acetobacter diazotrophicus (R12) and Azospirillum brasilense, Sp7 (ATCC 29729)) and to observe the effects of inoculation on growth of oil palm plantlets under in vitro conditions. The experiment was laid out in a completely randomized design with twenty-five replicates and harvested after 60 days of growth (D 60). The observations involved N2 fixation activities by acetylene reduction assay, root fresh weight (g), primary and secondary root numbers, leaf chlorophyll content and bacteria-root colonization at D 60. Results of the experiment showed that locally isolated A. diazotrophicus (R12) and A. brasilense (Sp7), were found to have the potential of inducing root formation of tissue cultured oil palm shoots (Elaeis guineensis Jacq. clone L295-1/177-1/16) and better shoot growm. A. brasilense (Sp7) could induce better rooting on the in vitro oil palm shoots compared to A. diazotrophicus (R12). Positive interactions between the bacterial inocula and roots of tissue cultured oil palm plantlets were recorded, which resulted in enhancing growth of the host plants. The plantlets inoculated with Sp7 showed the highest fresh weight (g) followed by control 1 (MS + NAA), R12 and Control 2 (Sp7k) at D60. The root fresh weight (g) and number of primary and secondary roots of the inoculated plantlets (Sp7 and R12) were also high compared to the controls. The Acetylene Reduction Assay (ARA) indicated the N2 fixation ability of the diazotrophs (Sp7 and R12 could fix up to 0.965 and 1.181 μmol C2H4 g-1 fresh weight h-1, respectively). The inocula could hence be used as microbial fertilizer for the clonal propagated plantlets of oil palms. © 2007 Asian Network for Scientific Information.