<p>Avocado is a crop that requires edaphic and environmental sustainability for its production and is related to the increasing depletion of natural resources. To ameliorate the situation, microorganisms that promote plant growth allow us to achieve sustainability goals, functioning as complementary to inorganic fertilizers, and representing an alternative to the high costs of these inputs. In this study, a soilless culture of avocado rootstocks was established, and the effects of nutrient concentration in vegetative tissue, growth, and root development were evaluated by inoculation with arbuscular mycorrhiza-forming fungi, plant growth-promoting rhizobacteria, and phosphate rock applied in the seed stage. The study was conducted in a greenhouse using a disinfected substrate (perlite and agricultural foam) with a 2³ factorial experimental design and evaluated at 103 DAS. Treatments with bacteria consisted of a consortium of <i>P. tolassii</i> (A46, P61), <i>B. pumilus</i> (R44-DsRed), <i>and A. xylosoxidans</i> (C56), inoculated directly into each seed. The AMF species were <i>R. intraradices </i> and were inoculated through a trap culture. Greater length and root volume were obtained by inoculation with PGPR, and less than 10% mycorrhizal colonization was obtained, which was insufficient to stimulate growth in seedlings; higher concentrations of N, P, and K in vegetative tissue were obtained, which were related to PGPR inoculation and RF application. Regarding height, the best results were obtained with AMF, PGPR, and PR treatment. In addition, the most abundant colonization with fluorescent bacteria was observed in this treatment. In conclusion, microorganism inoculation favored the development of avocado seedlings and improved root development and architecture.</p>