| Summary: | The production of eight phytohormones by <i>Trichoderma</i> species is described, as well as the 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD) activity, which diverts the ethylene biosynthetic pathway in plants. The use of the <i>Trichoderma</i> strains <i>T. virens</i> T49, <i>T. longibrachiatum</i> T68, <i>T. spirale</i> T75 and <i>T. harzianum</i> T115 served to demonstrate the diverse production of the phytohormones gibberellins (GA) GA<sub>1</sub> and GA<sub>4</sub>, abscisic acid (ABA), salicylic acid (SA), auxin (indole-3-acetic acid: IAA) and the cytokinins (CK) dihydrozeatin (DHZ), isopenteniladenine (iP) and trans-zeatin (tZ) in this genus. Such production is dependent on strain and/or culture medium. These four strains showed different degrees of wheat root colonization. Fresh and dry weights, conductance, H<sub>2</sub>O<sub>2</sub> content and antioxidant activities such as superoxide dismutase, peroxidase and catalase were analyzed, under optimal irrigation and water stress conditions, on 30-days-old wheat plants treated with four-day-old <i>Trichoderma</i> cultures, obtained from potato dextrose broth (PDB) and PDB-tryptophan (Trp). The application of <i>Trichoderma</i> PDB cultures to wheat plants could be linked to the plants’ ability to adapt the antioxidant machinery and to tolerate water stress. Plants treated with PDB cultures of T49 and T115 had the significantly highest weights under water stress. Compared to controls, treatments with strains T68 and T75, with constrained GA<sub>1</sub> and GA<sub>4</sub> production, resulted in smaller plants regardless of fungal growth medium and irrigation regime.
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