Efficiency of Trichoderma spp. as a growth promoter of cowpea (Vigna unguiculata) and analysis of phosphate solubilization and indole acetic acid synthesis

The aim of this study was to determine the efficiency of Trichoderma spp. in promoting the growth of cowpea plants. Strains were isolated from Tocantins savannah soils. Twenty-one isolates were evaluated in vitro for their ability to solubilize calcium phosphate and synthesize indole acetic acid (IAA). The soil samples were characterized physicochemically before planting. Eleven isolates were selected to evaluate the promotion of cowpea plant growth in the greenhouse in soil fertilized with phosphorite in 1.7-L pots. Then, at 32 and 45 days after planting (DAP), we determined the plant height (PH), root length (RL), dry matter of the aerial part (DMAP), root dry matter, total dry matter (TDM), relative efficiency (RE), and phosphate utilization efficiency (P-UEF) of the cowpea plants. The Trichoderma isolates showed a greater ability to synthesize IAA and solubilize phosphate than the controls. The best isolates for solubilizing phosphate were UFT 63, UFT 79, UFT 85, and UFT 201. The isolates UFT 25, UFT 79, UFT 110, and UFT 201 were more efficient in synthesizing IAA using tryptophan. The Trichoderma isolates exhibited P-UEF, especially isolates UFT 57, UFT 201, and UFT 204, with values of 430, 282, and 359 %, respectively, compared to controls. Consequently, the isolate UFT 201 (T. asperelloides GJS 04-217) showed greater potential as a growth promoter for cowpea, with a 38 cm PH, 29 cm RL, 4.5 g DMAP, and 5.8 g TDM at 45 DAP and a 256 % phosphorus content and 269 % RE compared to the control without inoculation.