Phosphate solubilization by microorganisms from the rhizosphere of Pigeonpea genotypes grown in different soil

Abstract

P-solubilizing microorganisms were isolated from the rhizosphere of six genotypes of pigeonpea (Cajanus cajan L. Millsp.) grown in pots containing soil from six classes: “Luvissolo”, “Cambissolo”, “Cambissolo Eutrófico”, “Argissolo Vermelho Amarelo”, “Neossolo Regolítico” and “Vertissolo”. All soils came from the Northeast region of Brazil. Eighty-five isolates were fungi and 46 bacteria. Eleven fungal isolates came from “Cambisssolo Eutrófico” cultivated with the genotype D1-Type; fourteen and ten isolates of bacteria came from “Neossolo Regolítico” cultivated with genotype Moreilândia and D1-Type, respectively. For the other soil classes, the number of bacteria was much lower (2 isolates). In vitro phosphate solubilization by 131 microorganisms was performed after incubation in liquid medium containing 2000 mg L-1 of “Araxá” apatite. The majority of fungal isolates decreased the pH to the range from 2.0 to 4.0 and bacteria from 4.0 to 6.5. Soluble P averaged 122 and 15 mg P L-1 for fungi and bacteria, respectively. Fifteen fungi isolates (14 Aspergillus and 1 Penicillium) more able in solubilizing P in liquid medium were chosen for identification. The amount of solubilized P and the number of P-solubilizing isolates depended on the soil type and pigeonpea genotype. Further studies should be performed to elucidate these interactions.