New Strains of Trichoderma with Potential for Biocontrol and Plant Growth Promotion Improve Early Soybean Growth and Development

Bioformulations with Trichoderma strains offer cost-effective and sustainable options for integrated disease management and plant nutrition. Therefore, this study aimed to selected isolates of Trichoderma with antagonistic and plant growth-promoting potential, specifically in the early development stage of soybean seedlings. Trichoderma isolated from the soybean rhizosphere were screened to assess their antagonistic activity against three phytopathogens; as well as their capability for indole-3-acetic acid (IAA) synthesis and phosphate solubilization. Three promising were further examined for their tolerance to various in vitro conditions and agrochemicals. Experiments were performed to assess the effect of single inoculation and co-inoculation of strains on the growth and biochemical responses during early soybean development. Nine isolates showed effective antagonism against phytopathogens. Among them, T. reesei GT-31 and T. longibrachiatum GT-32 showed the highest IAA production, with 175.8 and 119.6 μg/mL, respectively, while the T. viride GT-8 showed the highest phosphate solubilization activity after 10 days of growth (285.6 μg P/mL). These strains displayed robust growth under various conditions and agrochemical treatments. The co-inoculation of three strains resulted in even higher dry shoot and root weights, increasing by 50.3% and 48.8%, respectively, compared to non-inoculated seedlings. Co-inoculated plants also exhibited elevated chlorophyll (31.9%), carotenoids (24.9%), flavonoids (13.2%), and phenolic compounds (42.3%). The results suggest that employing the three strains with beneficial mechanisms for plants could significantly enhance the growth and early development of soybean seedlings. Overall, these findings highlight the potential of these novel Trichoderma strains to enhance plant growth and offer benefits in soybean crops, providing a sustainable strategy for agriculture.