The aim of the present study was to compare the benefit to soybean in terms of phosphate solubilization and host plant growth under salt stress of the endophytic fungi Fusarium verticillioides RK01 and Humicola sp. KNU01. Endophyte F. verticillioides RK01 increased phosphate solubilization significantly more than Humicola sp. KNU01, as confirmed by increasing activities of acid phosphatase (1.0 U-1 g fwt), alkaline phosphatase (2.1 U-1 g fwt ) and fungal biomass (4.6 g), with a concurrent decrease in tri-calcium phosphate concentration in the culture medium. In a plant growth evaluation study, 0.1 M NaCl was added to pots containing soybean plants pre-treated with fungi. The salt-affected plants exhibited stunted growth due to a lower concentration of protein and higher level of lipid peroxidation than their controls. F. verticillioides RK01 and Humicola sp. KNU01 isolates significantly increased shoot length (7.3 % and 2.5 %) and protein content (59.1 % and 65.1 %), while inhibiting the lipid peroxidation level in salt stressed plants. Moreover, carotenoids, the activities of superoxide dismutase (SOD) and catalase were lower in plants affected by salinity than in non-stressed plants, whereas Humicola sp. KNU01 fungal association significantly mitigated oxidative stress by enhancing carotenoids (24.1 %) and SOD activity (61.2 %). F. verticillioides RK01 also triggered SOD activity to prevent oxidative damage. In addition, salt stress caused an increase of absicsic acid (ABA) in soybean plants, and F. verticillioides RK01 colonization effectively reduced ABA content in stressed plants. Salicylic acid (SA) is another plant hormone that was present in lower amounts in stressed plants, but the endophytic (F. verticillioides RK01 and Humicola sp. KNU01) fungal association increased SA content in salt-affected plants. The results of the present study indicate that the efficient phosphate solubilizing endophytic fungi F. verticillioides RK01 was more favorable to protect soybean plants against oxidative damage than Humicola sp. KNU01.
