Ilex Paraguariensis Hosts Root-Trichoderma Spp. with Plant-Growth-Promoting Traits: Characterization As Biological Control Agents and Biofertilizers

In this study, the effect of native plant-growth-promoting microorganisms (PGPM) as bio-inoculants was assessed as an alternative to improve Ilex paraguariensis Saint Hilaire growth in the nursery. Fourteen Trichoderma strains isolated from yerba mate roots were evaluated in vitro for their potential as biological control agents (BCA) and PGPM. The PGPM properties were evaluated through the strain's antagonistic activity against three fungal pathogens (Alternaria sp., F. oxysporum, and F. solani) plus the production of extracellular cell-wall-degrading enzymes such as chitinase, β-1,3-glucanase, and cellulase. These results were used to calculate different PGPM indices to select the strains with the optimal properties. Four Trichoderma strains: T. asperelloides LBM193, LBM204, LBM206, and Trichoderma sp. LBM202, were selected based on their indirect and direct PGPM properties used in an inoculation assay on yerba mate plants in greenhouse conditions. A highly significant positive effect of bio-inoculation with these Trichoderma strains was observed in one-year-old yerba mate seedlings. Inoculated plants exhibited a greater height, chlorophyll content, and dry weight than un-inoculated plants; those treated with LBM193 manifested the best results. Yerba mate plants treated with LBM202 exhibited a healthy appearance and were more vigorous, showing potential for biocontrol agent. In conclusion, yerba mate seedlings in the Misiones region were found to have a reservoir of Trichoderma species that increases the yield of this crop in the nursery and protects them from adverse biotic and abiotic agents.