Selection of chilli-pepper seedling's growth promoting rhizobacteria from an Amazonian savanna

ABSTRACT The genus Capsicum includes economically important species important species, widely used as food and condiment. A critical stage of its production is obtaining quality seedlings, better adapted to transplanting, vegetative and productive development. The use of plant growth-promoting rhizobacteria (PGPR) in the production of high-quality vegetable seedlings can contribute to a more efficient agriculture, less dependent on crop protection products and mineral fertilizers. Therefore, the aim of this study was to select PGPR from pepper plants in the Brazilian Amazon savanna, using the quality index (QI) as a selection criterion and to evaluate their ability to produce promoters of plant growth, such as indole-3-acetic acid (IAA), phosphate solubilization (SCa-P), and biological nitrogen fixation (BNF). The experiment was conducted in Randomized Block Design (RBD) with four replications and 139 treatments, including a positive control (PC) and a negative control (NC). The ten best isolates were identified molecularly and subjected to three biochemical tests. The ten best bacteria demonstrated high growth promotion of pepper seedlings in the in vivo tests. Although not all isolates in this group demonstrated SCa-P and BNF capabilities, all of the isolates produced IAA. The bacteria isolated from the rhizosphere promoted the production of seedlings with higher QI, but the selection of bacteria based solely on the production of IAA, SCa-P, and BNF in vitro may not be enough to find the best isolates for promoting growth in pepper seedlings, as not all exhibited these mechanisms even though they improved the quality index (QI) of the seedlings.