Azospirillum brasilense enhances in vitro rhizogenesis of Handroanthus impetiginosus (pink lapacho) in different culture media

• CONTEXT : Handroanthus impetiginosus is an ornamental tree used in urban forestry programs and landscaping, produces good timber, and has medicinal qualities. Clearing of natural forest has been increased and motivates to find techniques that optimize rhizogenesis to ex situ conservation and reforestation. •AIMS : This study evaluated Azospirillum brasilense as an enhancer of in vitro rooting of H. impetiginosus under different indole-3-butyric acid (IBA) pulse inductions and media formulations. •METHODS : In vitro shoots were induced with 0 to 50-μM IBA pulse for 3 days, transferred to two half-strength media (Murashige and Skoog salts with Gamborg’s vitamins [MSG] and woody plant medium), and inoculated or not with A. brasilense Cd or Az39 strains. •RESULTS : The statistic response surface methodology determined that both A. brasilense strains decreased auxin requirement for rooting up to 49 % in half-strength MSG. In this medium, Cd strain with 30-μM IBA pulse produced the 98 % of rooting shoots 21 days before uninoculated plants induced with the same IBA pulse. Also, the biometric parameter index increased from 127 to 286 % in shoots inoculated and induced with 0 to 30 μM IBA, relative to uninoculated. •CONCLUSION : Our results show that biofertilization with A. brasilense significantly promotes in vitro rooting of H. impetiginosus decreasing auxin requirements and micropropagation costs.