Effective biofertilizer Trichoderma spp. isolates with enzymatic activity and metabolites enhancing plant growth

Trichoderma species have been widely recognized as biofertilizer fungi for their ability to produce phytohormones and enhance plant growth. In our current study, fifteen strains of Trichoderma spp. (T1-T15) were screened for their capacity to produce phytohormones and metabolites eliciting plant growth. The stains were previously isolated from olive rhizosphere soil in northern Algeria. Plant growth promoting (PGP) potential of Trichoderma spp. was evaluated in vitro through the production of phosphatases, siderophores, hydrogen cyanide (HCN), and ammonia (NH3). Besides, plant growth phytohormones such as gibberellic acid and indole-3-acetic acid (IAA) were assessed quantitatively by a colorimetric assay. Results showed an effective potential of Trichoderma spp. in plant growth-promoting biomolecule production. Importantly, qualitative estimation of phosphate solubilization indicates that T10 gave the highest phosphate solubilization on medium Pikovskaya's with a solubilization index (SI) of 3, whereas, the high capacity nitrogen-fixing was related to T8. On the other hand, quantitative analysis of indole-3-acetic acid and gibberellic acid revealed a production varying between (1.30 μg mL^-1 to 21.15 μg mL^-1) and (0.53 μg mL^-1 to 7.87 μg mL^-1), respectively; the highest amount of both phytohormones was obtained by T11 isolate. Indeed, an analysis of ethyl acetate extracts of T11 isolate by high-performance liquid chromatography (HPLC) revealed a high amount (71.19 mg L^-1) of IAA. Overall, the results showed clearly that isolate T11 has promising plant growth-promoting properties. Hence, this native Trichoderma isolate (T11) identified as Trichoderma harzianum strain (OL587563) could be used later as biofertilizer for sustainable olive crop agriculture.