Trichoderma species and their consortia vary in their ability to regulate tomato growth and restore bacterial richness in severely disturbed soil

Certain Trichoderma species are known for their biocontrol and plant growth-promoting properties. However, their inconsistent performance across production systems remains a major barrier to widespread adoption, highlighting the need to understand the factors that influence their efficacy. Here, we examined how T. harzianum ( Th ) and T. virens ( Tv ), and their equal mix ( Tvh ) affect tomato growth and rhizosphere bacterial communities. We also assessed whether volatile compounds (VCs) emitted by altered bacterial communities influence the growth of Trichoderma and Fusarium oxysporum , a soilborne fungal pathogen of diverse crop species. Additionally, tomato plants grown in autoclaved soil (AS) were treated with Th , Tv , and Tvh to evaluate their effects in a soil with severely disrupted microbial communities. Amplicon metagenomics and culturing revealed that Tv and Tvh competitively excluded rhizosphere bacteria in non-autoclaved soil (NAS) but partially restored bacterial richness in AS. The Tv and Tvh treatments significantly enhanced tomato growth in both AS and NAS. Co-occurrence network analysis revealed bacterial taxa that potentially interact positively or negatively with Tv and Th , suggesting that rhizosphere bacteria may influence the plant growth-promoting ability of these Trichoderma spp. by affecting their abundance and persistence. VCs emitted by the culturable bacterial fractions following different Trichoderma treatments did not significantly impact the in vitro growth of Trichoderma or F. oxysporum . Overall, our findings suggest that certain Trichoderma species can engineer rhizosphere bacterial communities to support tomato growth and restore microbial richness in severely disturbed soils. • Trichoderma enhanced tomato growth in autoclaved and natural soils. • Trichoderma effects on rhizosphere bacterial communities differed by soil type. • Certain Trichoderma spp. competitively excluded rhizosphere bacteria. • Certain Trichoderma spp. restored bacterial richness in autoclaved soils. • Rhizosphere bacteria may promote or inhibit Trichoderma performance.