Conventional farming disrupts cooperation among phosphate solubilising bacteria isolated from Carica papaya’s rhizosphere

We tested the legacy of the farming system (conventional or organic) on the interactions among phosphate solubilizing bacteria (PSB) and phosphate (Pi) solubilisation. We determined the in vitro Pi solubilisation and production of organic acids by nine PSB (four from conventional and five from organic farming) isolated from the rhizospheres of Carica papya, grown in monoculture or in pairs (66 combinations). When grown in monoculture, PSB isolated from conventional farming solubilised more Pi, but when grown in pairs, these PSB solubilised the least Pi. Furthermore, when the pairs included only PSB isolated from conventional farming, no Pi-solubilising cooperation was observed, that is, Pi solubilisation by pairs was lower than in monoculture. When PSB isolated from organic farming were present in the pairs, ∼40% of the combinations resulted in Pi solubilising cooperation. Organic acid production was not related with Pi solubilisation. Our work demonstrated the existence of a farming system legacy influencing the biotic interactions among PSB, and that the output of the interactions (cooperation or antagonism) was not phylogenetically determined. Data highlighted that biotic interactions should be considered when screening for potential plant growth promoting bacteria.