Biofertilizing effect of putative plant growth promoting rhizobacteria in vitro and in tomatillo seedlings (Physalis ixocarpa Brot.)

It has been widely reported that rhizobacteria improve plant nutrition and growth. Therefore, they can be utilized to reduce the use of synthetic fertilizers. The mechanisms involved in rhizobacteria biofertilization includes phosphorus and potassium solubilization, nitrogen fixation, ammonia production, and phytohormones synthesis. In this study, 6 rhizobacteria strains were selected and identified based on a preliminary screening from wild plants of Physalis sp. and their biofertilization mechanisms were assessed in vitro. Of these isolates, four were further tested in tomatillo seedlings. The in vitro assays results indicated that the bacterium identified as Atlantibacter sp. showed activity in all biofertilization mechanisms evaluated, with the best results in phosphorus solubilization and indole acetic acid synthesis. In the seedlings experiment, the seedlings with bacterial treatments presented higher leaf weight (>349%) and root length (>11%) than the control. Seedlings treated with Priestia megaterium resulted in the highest height of seedlings, 140% compared to the control. In addition, P. megaterium and Acinetobacter calcoaceticus were significantly higher in the concentration of three minerals: K (54 and 37%), Ca (88 and 80%), and Mg (89 and 81%). Tested strains: P. megaterium, A. calcoaceticus, and Atlantibacter sp. demonstrated outstanding biochemical and agronomical characteristics in vitro and in vivo, making them excellent biofertilizers candidates for tomatillo crop production.