Dark septate endophytes present different potential to solubilize calcium, iron and aluminum phosphates

Abstract

Many microorganisms play a significant role in releasing phosphorus (P) from soil insoluble phosphates to crops. Here, we evaluated the ability of dark septate endophytes (DSE) to solubilize calcium, aluminum and iron phosphates. DSE were isolated from the roots of wheat (Triticum aestivum) and the forages Panicum coloratum and Chloris gayana, which are grown in slightly acidic and alkaline soils of the Argentine Pampas, respectively. Protocols to corroborate their endophytic nature were followed. Nine fungi were identified by morphological and molecular characteristics, and their sequences were deposited in GenBank. The isolates belonged to the same order and genera as DSE fungi recorded in other parts of the world. The temperature and pH requirements of the DSE strains were verified. To determine their ability to solubilize phosphate, we followed two in vitro methodologies: solid and liquid media. On solid medium, all isolates showed ability to solubilize calcium phosphate, three strains solubilized aluminum phosphate, and none of them solubilized iron phosphate. The DSE most efficient in solubilizing calcium phosphate were Ophiosphaerella sp. and Cochliobolus sp., followed by Setosphaeria rostrata. The strains Drechslera sp. (P6), Ophiosphaerella herpotricha and Drechslera sp. (12–15) were able to solubilize aluminum phosphate. In liquid medium, the isolates showed different ability to generate acidity and to solubilize phosphates. Drechslera sp. (12–15) was among the most efficient in solubilizing calcium phosphate, Curvularia sp. in solubilizing aluminum phosphate and Ophiosphaerella sp. in solubilizing iron phosphate. The results obtained combining both methodologies indicate that S. rostrata was not the best with each phosphate individually but showed the best global performance. DSE fungi are far less identified than other groups of fungi and bacteria as soil insoluble phosphate-solubilizing agents. However, they showed potential for application as biofertilizers in different soils to manage sustainable agroecosystems.