Abstract

Phosphate solubilization by microorganisms is an important process for increasing the bioavailability of phosphorus (P) to plants. This study aimed to: (a) in solid medium, isolate CaHPO₄-solubilizing and non-P-solubilizing microorganisms from the rhizosphere of guanandi (Calophyllum brasiliensis) collected from a nursery and the field; (b) in liquid media, quantify the ability of CaHPO₄-solubilizing isolates from the rhizosphere of guanandi to solubilize FePO₄; and (c) quantify indoleacetic acid (IAA) production by FePO₄-solubilizing rhizosphere microorganisms. Two guanandi plants, one cultivated in nursery and another from the field, were used for the isolation of FePO₄ and CaHPO₄-solubilizing bacteria and fungi. The largest population of P-solubilizing and non-P-solubilizing microorganisms was found in the rhizosphere of guanandi cuttings cultivated in the field. The abilities to solubilize FePO₄ and produce IAA are variable among guanandi rhizosphere isolates, where bacterial isolates produce higher levels of IAA than fungal isolates.

Key words: Phosphorus, auxin, phosphate solubilization, seedlings.