Isolation and Characterization of Phosphate Solubilizing Activity of Endophytic Fungi from Zingiberaceous Species

Phosphorus (P), which is one of the less available soil macronutrients, is important for plant growth and metabolism. A promising strategy to increase the P uptake by plants is by introducing Phosphate-Solubilizing Microorganisms (PSM) into the P-deficient regions, to convert P into soluble forms through organic acids secreted by the PSMs. The aim of this study was to characterize the phosphate solubilizing activity of endophytic fungi in wild Zingiberaceous species which is still underexplored followed by the evaluation of their organic acids production. Out of 35 endophytic fungal isolates, 4 Phosphate-Solubilizing Fungi (PSF), namely, Pestalotiopsis thailandica He06, Trichoderma atroviride El01, Trichoderma brevicrassum Am08 and Trichoderma scalesiae Al01, displayed the highest solubilization index (SI >1.0) based on plate assay. The highest amount of solubilized P in Pikovskaya broth was detected from the culture filtrate of P. thailandica (4.61 mg/L), followed by T. scalesiae (1.85 mg/L), T. brevicrassum (1.38 mg/L) and T. atroviride (1.33 mg/L) based on molybdate blue colorimetric method. The culture filtrate of P. thailandica was profiled using Gas-Chromatography-Mass Spectroscopy (GC-MS), which revealed most of the organic acids, such as butyric, glutamic, lauric, margaric, oleic, palmitic, phthalic, propionic and stearic acid at their lowest pH (<4.0) at the end of incubation. Of the acids, phthalic acid (pKa = 2.76) was in the largest amount based on the GC-MS analysis revealing its possible contribution in P solubilization. The study then promoted P. thailandica He06 as potential P solubilizing agent for the future in planta test to assess its efficacy in the field trial.